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This study describes the effects of floor system, digital dermatitis (DD) and interdigital dermatitis and heel-horn erosion (IDHE) on locomotion performance in 225 dairy cows of 12 commercial dairy herds. Nine herds were kept in cubicle houses with concrete passageways (either solid, slatted, or grooved concrete) and three herds were kept in straw yards. Animals were at most five times examined at monthly intervals for lesion severity of DD and IDHE and for locomotion score. Locomotion score was rated on a scale ranging from 1 to 5 (from normal to severe) and disturbed locomotion (lameness) was defined as a scoreor =3. A logistic regression model was used to analyze the 943 observations using lameness (yes/no) as outcome variable. The proportion of observations scored as lame (locomotion scoreor =3) increased from 18% 1 month after trimming to 29% at 4 months after trimming. Severe lesions of DD and IDHE were associated with a significantly higher proportion of lame cows. The proportion of animals with disturbed locomotion increased from 16% to 40% as the severity of DD increased and from 17% to 30% with increasing severity of IDHE lesions. Locomotion performance highly differed between the cubicle house and straw yard group. Only 1% of all gaits in straw yard cows were scored as lame, while in cubicle housed cows these percentages varied from 24% to 46% with grooved floors showing the highest average locomotion score. Due to the extreme low incidence of lameness in straw yards, the statistical analysis had to be restricted to observations on concrete floors (n=744). The logistic regression model with lameness (yes/no) as dependent variable and random effects of cow and herd resulted in Odds Ratios for severe DD and IDHE of, respectively, 3.2 and 3.2, both significantly larger than unity. Cows housed at grooved concrete floors showed the highest OR of 6.5 compared to solid concrete floors. Recovery of lameness was poor as disturbance in gait lasted several months.

A computer model for welfare assessment in laying hens was constructed. This model, named FOWEL (fowl welfare), uses a description of the production system as input and produces a welfare score as output. To assess the welfare status a formalized procedure based on scientific knowledge is applied. In FOWEL the production system is described using 25 attributes (space per hen, beak trimming, free range, etc.), each with two or more levels, together defining the characteristics of a production system. A weighting factor is used for each attribute, based on the available scientific knowledge of the effects of the attribute levels on the welfare aspects. The welfare score of a production system results from the attribute levels combined with the weighting factors. The results show that feeding level, space per hen, perches, water availability and nests were the most important attributes. The attribute free range was of minor importance. FOWEL includes a description of 22 production systems. The welfare score of cage systems was low, of barn and aviary systems medium, and of organic systems high. The presence of a free range resulted only in a small improvement in the welfare score. De auteurs beschrijven een computermodel dat de bijdrage van specifieke elementen van de huisvesting op de gezondheid en welzijn van hennen in diverse productiesystmen, inclusief het nut van een uitloopren, analyseert

Several claw shape measurements, horn hardness, and horn growth and wear were recorded monthly at 12 dairy farms to investigate the effect of floor type and changes in these traits over time. Herds were either housed on a slatted floor (SL), solid concrete floor (SC), grooved floor (GR), or on a straw yard (SY). Twenty cows per farm were selected and stratified by parity. Information on claw traits was recorded on right lateral hind claws between October 2002 and May 2003. In addition, lesion development of interdigital dermatitis and heel erosion (IDHE) and digital dermatitis (DD) was studied in both rear feet. No differences in claw traits were detected among groups on different floor types, with the exception of claw angle. Claw angles were smallest in cows on SY. Claws of cows on SC were steeper than those on SL and GR. The study provided no evidence that floor-related differences in claw lesions were related to differences in horn growth, wear, and resulting claw shape. Lesions of IDHE developed gradually over time and did not differ among flooring types. Cows in SY had the smallest lesion scores for DD, whereas cows on SL had significantly less DD than cows on SC and GR. Incidence of DD fluctuated over time. Development of different stages of DD was monitored in-depth. Both early and healed stages were rather changeable and often turned into other disease stages. Classical ulcerative lesions (stage M2) persisted for a long time, with 20% of the initially unaffected claws having active lesions of DD within 5 mo. The M2 lesions generally did not cure effectively after claw trimming, and frequent use of footbaths resulted in a poor prognosis for recovery.

Two experiments were conducted to study the effects of sward height (experiment I) and the distance between barn and pasture plot (experiment II) on cows’ visits to an automatic milking system (AMS) and other behaviour. The study was carried out in a situation in which grazing was combined with fully automatic milking. The cows had to visit the system voluntarily without interference of the farmer. The AMS was continuously available in the barn adjacent to the pasture. The pasture was divided into ten plots of 1 ha for the two experiments and the preceding habituation. The same group of 24 Holstein Friesian cows was used in both experiments. The cows were allowed to spend up to 15 h at pasture daily. The results of experiment I (rotational grazing) showed that the total number of AMS visits increased from 4.4 to 7.3 and that the number of milkings increased from 2.6 to 3.0 when sward height decreased (P

Automatic milking systems (AMS) enable cows to be milked without human interference. Such systems are more acceptable to consumers and from the animal welfare point of view if they can be combined with grazing in the summer season. In this study, grazing was combined with fully automatic milking for a group of 24 crossbred Holstein–Friesian cows. It was assumed that the cows would visit the AMS voluntarily. Zero grazing (G0) was compared with restricted grazing (cows could spend up to 12 h outdoors daily; G12) and unrestricted grazing (cows could spend up to 24 h daily at pasture; G24). The AMS was continuously available in the cowshed adjacent to the pasture of 1.5 ha. Water was available in the barn, but not at pasture. The average daily milking frequency was 2.3 in G24 compared with 2.5–2.8 in the other treatments (p

The introduction of fully automatic milking systems (AMS) on dairy farms can only succeed if cows visit the system more or less voluntarily, at regular intervals. This can be arranged by either forced or free cow traffic. In the case of forced cow traffic, the AMS is the only route from the lying area to the feeding area. An alternative is free cow traffic, where the cows can decide whether to visit the AMS or not. The behaviour in 3 x 20 crossbred Holstein Friesian dairy cows in three experiments (experiment Ia, Ib and II) was studied in a cubicle house with a selection system consisting of a selection stall and a concentrate feeder, simulating an AMS. Cows could obtain 250 g of concentrate in the system once every six hours. Actual milking occurred in a conventional milking parlour twice a day. Experiment Ia consisted of (1) a reference phase with no use of the selection system, (2) free cow traffic, (3) forced cow traffic, and (4) a reference phase. Experiment Ib was a repetition of experiment Ia. Experiment II was divided into (1) a reference phase with no use of the selection system, (2) forced cow traffic with two one-way passages between the feeding and lying areas, (3) forced cow traffic with one one-way passage, (4) free cow traffic with one free passage between the feeding and lying areas, and (5) free cow traffic with two such passages and (6) a reference phase. The number of visits paid to the selection system by individual cows appeared to be consistent in the different phases in each experiment (r = 0.52 in experiment I (P < 0.05); r = 0.68−0.86 (P < 0.01) in experiment II). In experiments Ia and Ib, cows seemed to visit the selection system more often during forced cow traffic than during free cow traffic, but this was because some of the cows did not visit the system at all during free cow traffic. Therefore, the differences were not significant. In experiment II, cows paid the same number of visits to the selection system during different types of cow traffic, but when two passages were open during free cow traffic, the cows visited the system less (P < 0.01). During forced cow traffic, cows spent more time standing on the slatted floor in the feeding area, spent less time standing at the feeding gate and made less journeys from the lying to the feeding area (significant in two of three experiments; P < 0.01). It was concluded that forced cow traffic may improve the frequency of visits to the AMS, but somewhat restricts the cows' behaviour, and may, therefore, be questionable. Free cow traffic could work if cows are previously conditioned to take the route to the AMS.

Opioid receptor densities were measured in the hippocampus of chronically stressed (tethered) pigs to study the involvement of endogenous opioid systems in stereotypy performance. Three groups of animals were housed tethered for 2 (n = 12), 5.5 (n = 12) and 8-9 months (n = 8), respectively, and the intensity of stereotypy performance was determined. Opioid receptor densities were measured post mortem, using membrane binding assays with [ 3H]naloxone as a ligand. A negative correlation was found between the density of opioid receptors and the intensity of stereotypy performance in the animals that had been housed tethered for 2 months. This correlation seemed to disappear with increasing duration of tethered housing. The data further suggest that, associated with the duration of tethered housing, there was a gradual decrease in the density of opioid receptors in the left hippocampal lobe of the low-stereotyping animals, but not in the right lobe, nor in the left and right lobes of the high-stereotypers. This suggests that chronic stress leads to a (asymmetrically expressed) progressive loss of opioid receptors in the hippocampus, and that stereotypies exert a mitigating effect on stress-induced changes in opioid receptor densities, supporting the hypothesis that stereotypies help the animals cope with the adverse effects of chronic stress.

The advantages and disadvantages are discussed of forcing cows to visit the automatic milking parlour regularly by making it the only way for them to obtain supplementary feeds, vs. allowing cows to choose the frequency of their visits to the parlour. An alternative routing method was studied, in which the cows could move freely between the feeding and lying areas, but were stimulated to visit the automatic parlour by making it the only way of accessing the concentrate feeder. Two experiments were conducted, each with 2 treatments and 20 Holstein Friesian dairy cows. In the first treatment of experiment 1, the concentrate feeder was accessible only via the automatic parlour, and in the second treatment of experiment 1, concentrates were freely accessible. In both cases a new portion of concentrate became available once every 2 h. In experiment 2, the concentrate feeder was available only via the automatic parlour. A new portion of concentrate became available every 2 h during the first treatment of this experiment and every 4 h during the second treatment. Results showed that allocation of concentrate in a feeder which can only be reached via the automatic parlour is a good stimulus to attract cows to the parlour on a regular basis, because the milking frequency of these groups increased, and the waiting time in front of the concentrate feeder and the number of aggressive interactions in this area decreased. It is concluded that it is better to make concentrate available once every 4 h than once every 2 h, because this increases concentrate intake and rest in the barn.

Effects of rearing conditions on the development of social relationships were investigated in female pigs. For that purpose, one group of piglets was reared in a poor environment (i.e., a commercially used indoor 4.2-m2 standard farrowing crate) and the other in an enriched environment (i.e., 0.5-ha outdoor pasture with half-open farrowing crates). After weaning, all piglets were housed in pairs under standard conditions. Dominant and subordinate individuals were distinguished within pairs and social relationships between members of a pair were studied in adulthood. The results show that pairs reared in a poor environment behave more aggresively. The subordinates of these pairs also develop symptoms indicative of chronic social stress exposure: i.e., they show a delayed onset of puberty, a smaller daily weight gain, and elevated basal cortisol levels that are also higher 5 h after an acute restraint stressor (tethering stress). No such deviations were found in subordinates reared in an enriched environment. It is concluded that rearing piglets in a poor environment may facilitate the development of social stress in adult (subordinate) pigs. Two underlying mechanisms may be proposed: a) deteriorated social skills lead to increased social stress, or b) a failure to cope with stressors in general, and the stress of being subordinate in particular, occurs in animals reared under poor conditions.

Long-term tethered housing of pigs, which is not unusual in modern pig breeding farms, largely impairs the animals in their movements and thus represents a condition of chronic restraint stress. Some tethered pigs display stereotypies, that can be blocked by the opiate receptor antagonist naloxone, suggesnng increased activity of endogenous opioid systems in these animals. We have used the tethered pig as a model to further investigate the role of opioids in changes in hormonal and physiological regulation induced by chronic stress

This study describes the effects of housing pigs under optimal climatic conditions in a Specific-Stress-Free (SSF) housing system on health, behavior, immunological responsiveness, and production performance of 78 pigs from 10 litters. Pigs housed in an SSF system, where they were neither mixed nor transported, were compared with a control group of pigs for which transport was simulated and which were mixed at approximately 25 kg; transportation to another location and mixing are usual procedures in two-site systems. The SSF pigs had a higher growth rate for the finishing period (P < .01), but this was a smaller improvement in performance than in previous studies, probably due to less mixing in this study. Clinical signs were hardly seen in the SSF group, but aggression after mixing caused ear lesions in the control group. Pigs that were not mixed had a higher response 12 and 18 h after an intradermal injection of phytohemagglutinin (P < .001) compared to the control pigs. At 1 d ad 1 mo after mixing the control pigs, more agonistic interactions were seen in these pigs compared with the SSF pigs (P < .05 and P < .01, respectively). In conclusion, health, welfare, and production performance of pigs are improved when pigs are kept in an SSF housing system where they are not mixed or transported.

Young growing pigs (18 kg) were housed in two climatically controlled respiration chambers and exposed to 5 different climatic environments. Per chamber 20 pigs were housed (two groups of 10 pigs). Climatic environment applied to the treatment-group in one chamber was sequentially 25/15°C + draught, 25°C, 25°C + draught, 15°C + draught and 15°C. The control-group in the other chamber was exposed to the same temperature regime, but draught was not applied. Each treatment lasted 2 days, with one day in between. The treatment 25/15°C consisted of a fluctuation in ambient temperature during 24 h (25°C during day time, 15°C during night time). With draught air velocity was increased from 0.2 m/s to 0.8 m/s and temperature of the air stream was 5 K lower than ambient temperature. Draught occurred at night during three periods of 2 h (21.00–23.00 h, 1.00–3.00 h and 5.00–7.00 h). Draughts were applied intermittently in these 2-h periods. Within such a draught period, draught was repeatedly applied on a 4 min on and 4 min off cycle. Heat production was measured during 24 h and activity was related to this. In the treatment-group two pigs had transponders implanted to measure body temperature. Results showed that heat production and activity-related heat production were increased during periods of draught. Body temperature was affected also during draught. Effects on body temperature lagged behind heat production and activity-related heat production. Moreover effects were dependent on the temperature at which the draught occurred. With constant ambient temperature and absence of draught such effects were not present. The effect of the influence of sudden changes in climatic environment on body temperature and heat production is stressed.

Agonistic behaviour during experimental social encounters between 2 unfamiliar pigs was studied in 10-week-old pigs reared in pens of 3.5 msuperscript 2 or 6.7 msuperscript 2. In 3.5 msuperscript 2 pens, pigs which became dominant in the experimental social encounters exhibited more abnormal agonistic behaviour than pigs reared in 6.7 msuperscript 2 pens. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Mice with the hereditary, monogenic obese-hyperglycemic syndrome (ob/ob) were shown to have smaller adenohypophyses in comparison to their normal littermates from an age of 4 weeks onward. The size of the pars intermedia of obese mice was not, however, significantly different from that of normal littermates. Morphometric criteria strongly suggest hyperactivity of the cells of the pars intermedia of obese hyperglycemic mice. The enhanced secretion of bioactive peptides of the pars intermedia may contribute to the diabetic aspects of the obesehyperglycemic syndrome. The hyperactivity of the pars intermedia is likely to be allophenic.

During the last three decades, rearing conditions for pigs have changed drastically (e.g. reduction in floor space and impoverishment of the environment). Very little is known about the longterm effects of the changed rearing conditions on the behaviour of pigs. However, knowledge on this point is of great practical interest if, for instance, disturbed behaviour like high levels of aggression or poor maternal behaviour appear to result from early-life conditions. Four litters of eight piglets each grew up in either a farrowing crate (4 m 2, fully slatted concrete floor) or in a pen with straw as litter (28 mS). The piglets stayed in these housing systems until the age of 8 weeks and were weaned at 6 weeks. At the end of Week 8, two gilts per litter from the crate and two gilts per litter from the straw-bedded pen were housed in a straw-bedded pen (8.4 m s) and kept for breeding. Two weeks before the expected farrowing, the gilts were individually housed in straw-bedded pens; the gilts were not restrained. During rearing (Weeks 1-8), direct observations were made on the behaviour of the piglets. Later the gilts were observed for 5 days before, during, and 13 days after, farrowing. Piglets in the straw-bedded pen performed more exploratory behaviour than piglets in the crate (P

There are indications that pigs may have difficulty in adapting to the constraints of intensive housing conditions. Pigs show a wide variation in adaptive responses when exposed to the same stressful situation. Aim of this thesis was to investigate whether the behavioural coping responses of young piglets reflect and predict more general profiles of reactivity to challenges, often referred to as coping styles, under different rearing and housing conditions. For this purpose, pigs were characterized early in life as `high-resisting` (HR) or `low-resisting` (LR) on the basis of their resistance response in a so-called Backtest, in which they were manually restrained in supine position. The major part of the thesis focused on the interaction between these individual coping characteristics of pigs and their housing environment, which was either barren or enriched with straw bedding. The experiments described in this thesis show that HR pigs are more aggressive than LR pigs and less flexible in adapting their behaviour to environmental changes. As the two types of pig differed in response to the dopamine-agonist apomorphine, some initial evidence is provided for a neurochemical background of these behavioural differences. In addition, individual coping or personality characteristics of pigs were reflected in immune reactivity and in their home pen behaviour in barren and enriched environments. HR and LR pigs adapted differently to barren housing conditions. Moreover, individual characteristics modulated the effects of rearing and housing conditions on the behavioural response to novelty, immune reactivity, prevalence of gastric lesions and behavioural development. Remarkably, for almost all of the variables that were affected by housing environment, the impact was much larger for LR than for HR pigs. Thus, individual characteristics of pigs affect their performance in different environments and should be taken into account when studying the impact of housing on their behaviour and welfare. The knowledge of individual coping or personality characteristics could be extended and used for finding the optimal match between pigs and their social and physical environment in pig husbandry.

Tether housing of female pigs in narrow, individual boxes represents a chronic stressor for the animals. Pigs that are housed tethered often develop behavioural disturbances, such as stereotypies, and changes in physiological regulation. The results of the studies described in the present thesis confirm and extend previous suggestions that there is an association between stereotypies and brain opioid activity. We found a negative correlation between the intensity of stereotypy performance and opioid receptor densities in the hippocampus and the hypothalamus of pigs which had been housed tethered for two months. This correlation seemed to disappear with increasing duration of tether housing, likely as a consequence of the gradual decrease in receptor density that occurred in pigs with low levels of stereotypies. This receptor decrease might reflect glucocorticoid-induced neuronal cell loss, since we also found a negative correlation between he salivary cortisol concentration and the number of neurons in the hippocampus in long-term tether housed pigs. These results accord with the idea that stereotypies represent a strategy to reduce adverse effects of chronic stress.The chronic stress of tether housing not only leads to the development of stereotypies, it can also induce changes in physiological responsivity to further stressful stimulation. The mechanisms underlying these changes likely include alterations in endogenous opioid systems. This is indicated by our finding that antagonism of endogenous opioid activity increased the heart rate response of pigs to a stressful challenge after long-term tether housing but not after loose housing. These results provide evidence indicating that long-term tether housing leads to an increased impact of endogenous opioid systems that attenuate physiological responses to additional acute stress.Taken together, the present thesis highlights changes in endogenous opioid activity that are induced by chronic stress and appear to prevent or reduce potentially harmful stress effects.

A computer-based decision support system for welfare assessment in pregnant sows was constructed. This system uses a description of a husbandry system as input and produces a welfare score on a scale from 0 to 10 as output. Pregnant sows were chosen as a case in search for a formalised, i.e. structured, transparent, yet flexible procedure to 'objectively' assess the overall welfare status of farm animals in relation to the housing and management system based on available (and undisputed) scientific knowledge. The procedure to construct the welfare model and to calculate welfare scores is described. Decision making is based on the needs and distress of the animal thus from the perspective of the animal.The sow welfare (SOWEL) model was validated using expert opinion in that there is a substantial agreement between pig welfare scientists and the model about the ranking of housing systems and, to a lesser degree, about the weighting of attributes of housing systems. The most important welfare-relevant attributes concern aspects of social contact, space, and substrate. The housing systems were roughly divided into low-, mid-, and high-welfare systems. Low-welfare systems were conventional housing in individual stalls and tethers, while high-welfare systems in our data set all provided substrate and outdoor access.For practical applications further development of the decision support system is recommended, as well as ongoing validation, upgrading and extending of the model, e.g. to other species. The results show that integrated welfare assessment based on available scientific knowledge is possible.Keywords : farm animal welfare assessment, pigs, applied ethology, housing systems, model, computer, knowledge base, expert system.

In this study of cow behaviour and managerial aspects of fully automatic milking, the emphasis was on implementing automatic milking systems (AMS) in cubicle houses in a way that suits cows and farmer. The starting points of the research were that the cows would visit the AMS voluntarily and that the system would be available almost continuously. The effects of the cows' social hierarchy, the cow traffic towards the AMS and the combination of grazing and fully automatic milking were studied.The cows' social hierarchy only affected the timing of forage eating and AMS visits. Cow routing procedures that more or less forced cows to visit the AMS because that was the only way they could reach the forage appeared to be questionable with regard to the cows' adaptation to the AMS environment. In these cases of forced cow routing, eating behaviour seemed to be postponed or even thwarted and there was more idle standing. Free cow traffic, during which cows could themselves decide when to visit the AMS, did not appear to suit the farmer because the milking frequency of individual cows was not sufficiently reliable. A third type of cow traffic in which cows could move freely between the feeding and lying areas but had to pass through the AMS to reach the concentrate feeder appeared to be a good solution for both the farmer and the cows. The cows paid sufficient visits to the AMS, had shorter waiting times in front of the concentrate feeder and less aggression was seen there. Supplying new concentrate every four hours instead of every two hours increased the time spent resting in the barn.It was found that grazing and fully automatic milking could be combined. When cows had access to a pasture they did return to the AMS by themselves several times a day, depending on the weather and the sward height. Cows spent more time indoors when the ambient temperature was high. At lower sward heights, they also spent more time indoors and at the feeding gate, paid more visits to the AMS and were milked more often. Distances of up to 350 m between the pasture and the barn did not affect the number of AMS visits.

Changing legislation and consumer attitudes towards the welfare of farm animals means that individual housing of dry sows will soon be illegal in the United Kingdom. Other European countries, and in particular those for whom the UK is an important export market (such as The Netherlands), are under pressure to follow suit. Group housing is generally believed to provide a higher degree of welfare than individual housing, because it allows the animal greater behavioural freedom. However, group housing does not eliminate behaviours such as stereotypies, which are associated with an inadequate environment and have long been the cornerstone of the (ethological) argument against individual dry sow housing. Also, group housing promotes the occurrence of agonistic behaviour, potentially reducing the welfare of most, if not all animals in the group. The present thesis addresses these undesirable behaviours in group housed sows, and investigates the role food level and the provision of straw may have to play in trying to reduce them. It also looks into the possibility of developing tests to identify gilts which are likely to develop these behaviours during their adult life, by assessing individual behavioural responses to a number of challenges before the animals reach puberty.In Chapter 1 the hypothesis was tested that food motivated pregnant sows need a substrate, for example straw, to express foraging behaviour. The absence of a suitable substrate may under certain conditions result in the development of abnormal oral activities, such as stereotypic chain and bar manipulation. The study described used 96 gilts, all between 1 and 3 weeks post service, which were entered into a 2 × 2 factorial design comparing food level (Low 1.8 kg/23 MJ day -1and High 3.2 kg/40 MJ day -1) and the provision of a foraging substrate (Straw and No straw). The gilts were loose housed in groups of 6 with individual stalls. Behaviour was recorded over the first two parities, by time sampling for the 2 and 6 hours after the start of feeding and over 24 hours using video recordings.The results show that activity levels were highest just after feeding, with low fed sows being more active than high fed sows. Most of the postprandial activity consisted of manipulating substrates. In low fed sows without straw, particularly in parity 2, this behaviour was mainly directed towards chains and bars, resulting in levels 3 to 4 times higher than in other groups. Low fed sows with straw directed their foraging behaviour mainly towards the straw. Chapter 1 concludes that in food restricted pregnant sows abnormal high levels of chain and bar manipulation can be prevented by providing straw which apparently acts as a foraging substrate.The second chapter described how the treatments applied in Chapter 1 affected the performance of the animals as well as their chronic and acute physiological stress responses. The latter was tested by injecting the pigs at the end of their second pregnancy with adrenocorticotrophic hormone, ACTH (1 iu kg -1live weight), which induces the adrenal cortex to release all available cortisol. Saliva samples were taken before and after the ACTH challenge, and baseline and response levels of salivary cortisol were assessed.The results emphasise the importance of straw: significantly more non-straw sows failed to start the second parity than straw sows. Food level showed expected differences in weight gain, with high fed sows gaining more weight and back fat over both pregnancies than low fed sows. Low fed animals with straw tended to gain more weight and back fat over both pregnancies than low fed sows without straw. Litter performance was not influenced by the straw treatment. High fed sows without straw were found to have the highest concentration of basal cortisol, but no treatment effects were found in increase of salivary cortisol concentrations in response to the challenge with ACTH. The chapter concludes that provision of straw may buffer the adverse effects of a low food level on weight and back fat gain in group-housed pregnant sows, but that it has no effect on reproductive performance. The results of the ACTH challenge tests suggest that physiological differences between treatments are most likely to be of an acute nature, rather than a chronic one.In Chapter 3, the focus of attention is moved towards large groups of dynamic sows. It addresses the hypothesis that hunger may be a cause of increased aggression between animals. For this study, sixteen groups of 5 gilts were introduced over 8 months to 1 of 2 dynamic groups in a deep straw yard. Sows in each group were receiving a different level of food from an electronic sow feeding system: High (3.0 kg / 38 MJ day -1) and Low (1.6 kg / 20 MJ day -1). The behaviour of the animals was recorded throughout both pregnancies using a time sampling technique. The total number of animals in each dynamic group was maintained at around 30, through the use of additional sows. The results indicate, as expected, that food level affects body weight: high fed sows were heavier than low fed sows.However, no effect of the food treatment was found on litter size or litter performance. Behaviour observations showed a low fed sows to be more active and manipulating the straw more than H sows. However, food level did not affect the number of aggressive interactions, or the level of skin damage on the sows. In contrast, the introduction of new animals to the groups did: pigs were more involved in aggressive interactions on the day they were introduced, than on other pig's introduction days and no introduction days. Average skin lesions per experimental sow were also higher in the days immediately following introduction. The conclusion of Chapter 3 is that in a sequential feeding system with plentiful straw, aggression is not influenced by the level of food. In these systems, the major factor giving rise to aggression is the introduction of new animals to the resident group.In Chapter 4 the spatial organisation of the dynamic groups of pigs used in the previous chapter was investigated more closely. Although Chapter 3 suggested that food level does not have an overriding effect on aggression, an increased food motivation may well affect the use of the pen by the animals, through changes in personal space requirements and / or the "defense" of particular areas. In order to do this, the spatial organisation of the animals was recorded throughout both pregnancies on a floor plan of the building, at fortnightly intervals. From these a range of spatial parameters were calculated: the frequency of visiting predetermined pen areas, the average location of the pig in the pen, the average inter individual distance, the distance and identity of the nearest neighbour and the proportion of observations an animal spends within a two meter range of another animal.The effects of food level were restricted to an increased use of the drinker area by high fed sows, and an increased use of the feeder area by low fed sows. The time since introduction of a new subgroup affected all spatial parameters, with the average inter-individual distance between resident and new animals decreasing, and that within subgroups increasing. The chapter concludes that social integration appears to be a staged progress, starting off with a peak in agonistic behaviour, followed by an increased use of the same areas of the pen. The final stage, which involves a random sharing of the immediate area around an individual, was not achieved before pigs were taken out of the group for farrowing.The fifth chapter described an investigation into the consistency of a gilt's behavioural responses between and within test situations, aiming to relate them to the development of undesirable behaviours in the group housed adult animal. To achieve this, behavioural responses of gilts were tested under 4 different circumstances. Gilts were housed in two series of 16 groups each (n= 6 or 7 gilts per group). The test situations were: Situation 1: an open field with a novel stimulus (bucket or human); Situation 2: individual access to food for 15 minutes after a 20 hour period of food deprivation; Situation 3: competition for food after food deprivation; Situation 4: general activity and feeding behaviour in a group over a 24 hour period.Situations 1 and 2 were assessed 4 and 3 times over a 2 and 1 week period, respectively. Both showed high levels of consistency in the behavioural responses of the gilts. Principal components analyses was used to reduce the number of variables per test situation and facilitate measurement of consistency across test situations. The amount of variation explained by the first component was generally more than twice that explained by any subsequent components. The only significant correlation between factor scores calculated from the first components was found between Situation 1 and 2 in the first series. None of the calculated factor scores showed bi- or multimodal distributions. The chapter concludes that, whilst over a short period of time gilts respond consistently to a specific challenge, they do not display the same consistency when challenged in a different context. This lack of inter-situation correlations, plus the absence of multimodal distributions, fails to support the view that behavioural "types" of gilts exist.The General Discussion addresses the practical implications of the findings in Chapters 1 to 5 in three parts. Part 1 suggests that group housing may result in reduced development of stereotypic behaviour, even though factors such as food level and straw provision may have an even greater effect. It also queries the relationship between the feeder area and the development of abnormal repetitive behaviour: does the association with food reinforce of this area reinforce the behaviour? Finally, on the subject of stereotypies, it highlights the need for continued research into alternative substrates which can be used in circumstances were straw is not an option. In Part 2, the discussion on large dynamic groups starts off by highlighting the fear of many producers who have to convert to group housing, that aggressive behaviour will dramatically reduce the welfare of the animals. It suggests that dynamic group housing systems, in which aggression is an inevitable consequence of the constant restructuring of the social organisation, should preferably not be operated in the absence of a substrate.Further more, the frequency of introducing sows to an existing group should be kept to a minimum, for example by operating semi-dynamic groups. In the final section of Part 2, the stability of the subgroup is discussed, and the concept of incorporating separate lying areas supported. Part 3 reaffirms that pigs are individuals, and that their individuality might be based on differences in a range of underlying character traits. It questions the feasibility of identifying gilts unable to "cope" with challenges in adult life, although it may well be possible to identify behavioural or physiological predictors of undesirable behaviour shortly before they start developing. Finally, it acknowledges the fact that individual behavioural differences between pigs are both unavoidable as well as desirable, but that they do demand a higher level of stockmanship if sows are kept in groups, compared to individually housed animals.

IntroductionThe main purpose of the studies described in this thesis was to gain more insight in the regulation of the hypothalamic-pituitary-adrenocorticaI (HPA) system and the mechanisms underlying adaptation to chronic stress in female pigs. The function of the HPA axis, which coordinates multiple neuroendocrine and metabolic responses to stressors, has been subject of extensive basic and clinical research. HPA-activation by stressful stimuli results in an increase in circulating adrenocorticotropic hormone (ACTH) and consequently of glucocorticoid hormones. A brief review of stress and HPA functions is given in Chapter 1.It has been demonstrated in a variety of species that exposure to chronic or repeated stress may induce long-term changes in the regulation of the HPA axis. These changes may occur at the following levels: 1) extrahypothalarnic centers modulating the activity of neurons in the paraventricular nucleus of the hypothalamus that secrete corticotropin-releasing hormone (CRH) and/or other ACTH secretagogues; 2) hypothalamic sites releasing ACTH secretagogues; 3) ACTH-secreting cells in the anterior lobe of the pituitary; 4) glucocorticoid secreting cells in the adrenal cortex.This project was mainly focussed on the regulation of pituitary-adrenocortical function during chronic stress. Long-term restraint of female pigs by a neck-tether was used as a chronic stress paradigm. Previous studies have demonstrated that tethered pigs may develop behavioural, hormonal, and cardiovascular disturbances characteristic for chronic stress. In Chapters 2 and 3 of this thesis we showed that prolonged tethered housing leads to a sustained elevation of basal plasma cortisol concentrations. Chapters 4, 5 and 6 provide evidence that chronic stress may induce long-term changes at the level of the adrenal cortex, resulting in increased steroidogenic capacity and sensitivity for ACTH. No change was found in the sensitivity of the pituitary for CRH or vasopressin. There was no indication for an increase in basal ACTH levels, but the ACTH response to a superimposed acute stress appeared to be reduced during chronic stress. The hypersecretion of cortisol may therefore well be a consequence of stress- induced changes in adrenocortical function. Moreover, chronic stress leads to an increase in the activity of- opioid systems that inhibit pituitary-adrenal responses to additional acute stressors. These alterations in opioid systems may be of adaptive value in that they prevent excessive reactions of the pituitary-adrenal system during chronic stress. This may also underlie the transient nature of the hypercortisolaemia.Pituitary-Adrenocortical Function after Chronic StressHypercortisolaemiaThere is ample evidence, particularly from studies in the rat, that repeated exposure to stressors may produce an increase in the activity of the adrenocortical system, as evidenced by increased circulating corticosteroid concentrations andlor adrenocortical hypertrophy and increased adrenal weight Indeed, in female pigs we found that chronic stress induces long-term elevated basal cortisol levels (Chapters 2 and 3). This hypercortisolaemia, which develops within the first weeks of tethered housing, is evident in every phase of the oestrous cycle of the pigs. It is particularly obvious during the luteal phase of the oestrous cycle when cortisol levels remain rather stable (Chapter 2). In addition, our data reveal circadian differences in the effect of chronic stress on HPA- regulation. Elevated cortisol concentrations are most pronounced in the evening, i.e. during the nadir of cortisol secretion, and lead to a flattened diurnal rhythm of cortisol secretion during chronic restraint stress (Chapter 3). These findings correspond with observations in rats and in man, that chronic stressinduced corticosteroid levels are increased during the trough of circadian adrenocortical activity Determination of cortisol over a 24-hour period demonstrated that elevated evening cortisol concentrations during chronic stress are not the result of a stress-induced shift in the phase of the cortisol rhythm (Chapter 3).Chronic stress may conceivably cause "facilitation" of the HPA system, either by increasing its sensitivity to stimulus input or by decreasing its sensitivity to negative glucocorticoid feedback, or both, so that elevated corticosteroid concentrations are maintained throughout the period of stress. It is well-known that ACTH has a trophic effect on the adrenal cortex. Prolonged ACTH stimulation (e.g., during chronic stress) may therefore lead to hypertrophic enlargement of the adrenal gland, resulting in increased output of glucocorticoids in response to this peptide with time. Furthermore, in rats it has been reported that chronic stress may result in a persistent decrease in feedback sensitivity to corticosteroids. Akana and co-workers have suggested that there is a high sensitivity to glucocorticoid feedback during the trough of the circadian corticosteroid rhythm, accompanied by a diminished (or absent) circadian-dependent drive to CRH secretion in rats. Moreover, they suggested that the circadian rise in plasma corticocosteroid levels is a result of stimulated CRH secretion as a consequence of diminished sensitivity to steroid feedback. One may speculate that the increase in evening, but not in morning plasma cortisol levels during chronic stress, described in Chapter 3, is in part the result of stress-induced changes in feedback sensitivity to circulating cortisol. In other words, the hypothalamus remains insensitive to cortisol, resulting in increased cortisol levels throughout the day.Increased Sensitivity and Capacity of the Adrenal CortexWe found that the chronic hypersecretion of cortisol in tethered pigs does not coincide with an increase in plasma levels ofβ-endorphin (Chapter 2), a peptide co-secreted with ACTH from the pituitary corticotroph cell. It may therefore be inferred that the hypercortisolaemia is not a reflection of a sustained increase in ACTH release from the pituitary, although basal plasma ACTH levels were not measured in those experiments. Several reports in rats, showing that elevated glucocorticoid levels during exposure to chronic stress are not necessarily associated with significant increases in plasma ACTH, support this contention.Our data (Chapters 4, 5 and 6) provide evidence for stress-induced changes in HPA- regulation. In pigs tethered for a period of 10-11 weeks, the ACTH response to a superimposed stressor (acute nose-sling stress) appears to be reduced as compared with loose housing, whereas the cortisol response remains unaltered (Chapter 5). These data indicate that the sensitivity of the adrenal cortex to circulating ACTH increases as a result of chronic stress. This finding is supported by the study described in Chapter 6, in which the cortisol/ACTH ratio after CRH treatment in tethered pigs shows a two-fold increase when compared with loose housed pigs. Moreover, challenge with exogenous ACTH(1-24) reveals that the capacity of the adrenal cortex to secrete cortisol increases during chronic stress (Chapter 4), which is in line with findings of other studies in pigs1 and other species. This increase in adrenocortical capacity may result from a hypertrophic enlargement of the adrenal gland. All in all, our observations point to the adrenal cortex as one of the dominant sites where functional changes occur during chronic stress.We speculate that these changes in adrenocortical function may well underlie the hypercortisolaemia in tethered pigs (Chapters 2 and 3). Although ACTH is generally considered to be the most important factor in the control of glucocorticoid secretion from the adrenal cortex, there is increasing evidence that steroidogenesis is also under control of neural inputs at the level of the adrenal gland, which can modulate adrenocortical sensitivity to ACTH and thereby control the secretory activity of the adrenal cortex. In rats it has been reported that locally secreted CRH is likely to mediate such an increase in adrenal sensitivity to ACTH by stimulating the blood flow through the adrenal gland, although, to our knowledge, no such mechanism has (yet) been demonstrated in the pig. In this context, it is interesting to note that a challenge with vasopressin in our study produced an approximately five-fold greater cortisol/ACTH ratio than a challenge with CRH (Chapter 6). This implies that in the pig, vasopressin can stimulate corticosteroidogenesis beyond that induced by vasopressin-stimulated ACTH release, possibly by a direct effect on the adrenal gland. In addition, our data indicate a synergism between vasopressin and CRH in their cortisol releasing effects. which may also result from a vasopressin-induced increase in the responsiveness of the adrenal cortex to ACTH.Effects of Housing Conditions on Adrenocortical CapacityIt was interesting to find in our study that housing factors different from the physical restraint of tethered housing per se play a role in the development of adaptive changes in the steroidogenic capacity of the adrenal cortex during chronic stress. We showed that the increase in the cortisol response to challenge with exogenous ACTH(1-24) is considerably more pronounced and persistent in tethered pigs deprived of visual and tactile contacts with conspecifics and with very limited visual control over the environment, than in tethered pigs that have such possibilities, albeit to a limited degree (Chapter 4). The least restricted pigs were separated by horizontal bars, thus allowing social contacts with neighbouring pigs and visual control over the environment. In the most restricted pigs, closed partitions between the pens precluded social interactions and severely limited their visual range. It seems likely that the relative lack of visual information from the environment reduces the predictability of environmental changes and increases uncertainty for those animals, thereby contributing to the stress experienced by the animals. As has been discussed in Chapter 1, low predictability or uncertainty is generally recognized as a characteristic of stressful situations. Furthermore, it has been demonstrated that lack of social interactions with conspecifics may affect stress responses, especially with respect to the HPA axis. Thus, both reduced visual control and social restriction are likely to be important factors contributing to the changes in adrenocortical function observed earlier. These findings underscore the notion that psychological factors are important activators of the HPA axis.Sensitivity of the PituitarySo far, effects of chronic stress on adrenocortical function have been emphasized. Studies in rats have provided evidence that chronic stress may also lead to changes in the sensitivity of the pituitary for hypothalamic peptides regulating ACTH secretion, possibly as a consequence of changes in expression and secretion of these secretagogues. Repeated activation of the HPA system may lead to plastic changes in hypothalamic CRH neurons, resulting in increased expression of vasopressin in CRH- containing neurons and increased vasopressinergic stores in vesicles in the median eminence, leading to an increased ratio of vasopressin/CRH that is secreted.Hashimoto et al. found that the pituitary-adrenocortical response to vasopressin was enhanced in rats that were chronically immobilized as compared with unstressed controls, whereas responses to exogenous CRH remained unaltered in these animals. They suggested that chronic stress caused a hypersensitivity of the pituitary to vasopressin. In pigs tethered for a 10 to 13week period, the absolute ACTH and cortisol responses to exogenous CRH, vasopressin, or a combination of these two peptides (Chapter 6) are not significantly altered, as compared with loose housed control animals. The cortisol/ACTH ratio after CRH treatment, however, is significantly higher in tethered than in loose pigs.In summary, chronic stress leads to an increase in the sensitivity and capacity of the adrenal cortex to circulating ACTH, whereas the sensitivity of the pituitary to stimulation with CRH and/or vasopressin in pigs remains unaltered. These findings again point to adaptive changes in adrenocortical function as a consequence of stress, possibly mediated by mechanisms modulating adrenocortical sensitivity to ACTH.Adaptation to Chronic StressActivation of stress systems results in behavioural and physiological changes which allow the organism to adapt. In general, adaptive responses to stress involve a redirection of both behaviour and energy. Simultaneously, digestion and anabolic processes, such as growth, reproduction and immune function are suppressed. It appears that the ability to regulate the stress response appropriately may be as important as the ability to initiate it. Containment of the stress response is crucial to avoid detrimental consequences of excessive mobilization of resources and behavioural responses.As stated earlier, chronically stressed pigs develop changes in adrenocortical function so that further responsiveness of the adrenal system is maintained, despite elevated glucocorticoid levels. The hypersecretion of cortisol -is maintained for at least three complete oestrous cycles after tethering (approximately 9 weeks) and thereafter it gradually disappears (Chapter 3). This suggests that adaptive changes occur during chronic stress affecting HPA-activity and leading to normalization of adrenocortical output. Nevertheless, the fact that both the sensitivity and the capacity of the adrenal cortex are increased during the same period (Chapters 4, 5, and 6), suggests that adrenocortical function has chronically changed. Moreover, the apparent adaptation of cortisol levels during chronic stress does not imply normalization of brain mechanisms controlling cortisol concentrations in response to challenges or stressors (Chapter 5). Presumably, adaptation consists in changing certain "set-points" in order to meet the new demands.The mechanisms responsible for these adaptive changes during chronic stress likely include an increase in the activity of endogenous opioid systems. It has been demonstrated that tethered sows may develop stereotypies associated with and dependent on the activation of opioid systems. Administration of naloxone, a specific opiate receptor antagonist, has shown to block or reduce the occurrence of this invariant behaviour. Although we did not quantify behaviour in our experiments, we also observed performance of stereotypies such as bar or chain biting and sham chewing in tethered gilts. Brain opioid systems, however, are not only involved in the neurochemical control of behaviour, e.g., of stereotypies, but have also been implicated in the regulation of the activity of several hormonal systems, including the HPA axis. Thus, chronic stress of tethered housing leads to increased activity of endogenous opioid systems and may therefore affect the HPA axis by means of opioids. In view of this hypothesis, we subjected both tethered and loose housed female pigs to an acute nose-sling challenge. The enhanced and prolonged ACTH and cortisol responses to nose-sling challenge after pretreatment with naloxone (Chapter 5) point to an activation of both the HPA system and the endogenous opioid systems. This naloxone-dependent increment in ACTH and the cortisol responses are significantly greater in animals tethered for a 10 to 11-week period than in loose animals, indicating that the opioidmediated suppression of the pituitary-adrenocortical response is increased during chronic stress (Chapter 5). It may be speculated that the gradual reduction of the hypercortisolaemia, observed during the same period of tethered housing is also a consequence of an increase in the impact of endogenous opioid systems. Based on our findings and on literature data, we postulate the hypothalamus to be a key central site for the mediation of this effect of opioids (Chapter 5). All in all, these data indicate that chronic stress of tethered housing leads to adaptive changes in opioid systems modifying behavioural as well as endocrine reactions.Individual Differences in Pituitary-Adrenocortical ResponsesA major focus of the stress and coping literature has been on individual differences in reactivity to stressors under challenging conditions. There is ample evidence that not all individuals of the same species experience the same situation as stressful, and, vice versa, that the same stressors do not necessarily result in identical behavioural and peripheral responses. As mentioned in the general introduction, differences between individuals in coping with stressful situations appear to be related to genetic constitution, as well as to prior (particularly: early life) experiences, and the actual physiological and psychological state of the organism. Important in this respect is the way in which an individual estimates the situation and its possibilities to cope with the situation.In the present project, we obtained evidence that pigs express individual variability in the (re)activity of the pituitary-adrenocortical system in adapting to the chronic stress of tethered housing. There are, for example, great differences in. basal cortisol levels between individual pigs during tethered housing (Chapter 3), particularly with respect to the moment of disappearance of the stress-induced hypercortisolaemia. In addition, as described in the experiment in Chapter 4, considerable differences are found between individual animals in their cortisol responses to challenge with exogenous ACTH. Within the same pigs, however, the cortisol response to repeated challenge with ACTH (measured in the loose housed control groups) is consistent during an 18-week period of loose housing. This is in good agreement with findings of others in pigs, indicating that the adrenocortical reactivity is an individual characteristic that remains stable in time. The interanimal differences in the adrenocortical reactivity pattern are particularly evident during exposure to chronic stress (Chapter 4). It is noteworthy, that the greatest individual differences are observed in animals that are tethered housed under the most restricted conditions (i.e. lacking possibilities for visual and tactile contacts with conspecifics and with very limited visual control over the environment).It may be argued that variability among individuals in their ability to adapt to conditions inducing stress responses reflects differences in neuroendocrine susceptibility to the stressful situation and the degree of control sensed by the individuals. Hessing demonstrated that types of pigs can be identified based on individual behavioural characteristics and that those characteristics are related to different physiological strategies displayed in response to stressors. In addition, Schouten and collaborators not only showed individual differences in performance of stress-induced stereotypies between tethered pigs, but also in feeding- induced cardiovascular responses during prolonged tethered housing. It has been suggested that these differences in behavioural and physiological reactions may represent individual coping characteristics of the animals involved.Practical ImplicationsConsequences of Chronic Stress and HypercortisolaemiaIn the present study, prolonged tethered housing of female pigs was used as a chronic stress paradigm. Although this husbandry system, which is used in intensive pig farming, may be advantageous from an economical point of view, the well-being of the animals is lost sight of. Tethered pigs are housed in a barren environment with physical restraint and social restriction, which may have consequences for the animal's behavioural and physiological performance.We showed that tethered pigs develop a hypercortisolaemia. Chronic elevation of cortisol levels may have profound physiological consequences. As has been discussed in Chapter 1, chronic activation of the catabolic stress response may ultimately lead to various pathophysiological states. The systems responsible for reproduction, growth and immunity are directly linked to the stress system, and each is profoundly influenced by the effectors of the stress response. It has been reported that tethered housing of pigs may induce reproductive disorders, such as a reduced rate of oestrous detection (e.g., occurrence of silent oestrus) and a reduced pregnancy rate. The present findings show that 3-6 weeks of tethered housing results in significantly decreased levels of plasma progesterone throughout the oestrous cycle (Chapter 2). No effects of 3-6 weeks of chronic stress were found on plasma LH concentrations, oestrous behaviour or on the length of the oestrous cycle. Nonetheless, it is well possible that more prolonged tethered housing may disrupt LH secretion or ovarian function and thereby adversely affect reproductive performance in the pig. Indeed, Helmond, Soede and Kemp recently showed that in tethered sows the duration of oestrous behaviour was significantly shorter as compared with loose housed sows (to be published). Moreover, the pulsatile LH release in that study seemed to be more "chaotic" in the tethered animals.Besides suppression of reproductive performance, long-term activation of the HPA axis and consequently elevated cortisol levels may have metabolic (myopathy, fatigue, changes in glycemia) and cardiovascular consequences (hypertension). Furthermore, compromised growth and tissue repair, and peptic ulceration may occur, as well as immunosuppression. In this respect, parallels have been drawn between the chronically stressed animal model and several human diseases. It has been demonstrated in clinical studies that some common psychiatric disorders, such as depression, panic disorder, anxiety and anorexia nervosa, may represent disorders occurring in response to stress. Hypersecretion of glucocorticoids and resistance to glucocorticoid negative feedback have been shown to occur in people with anorexia nervosa and major depression.In addition to changes in HPA regulation, long-term exposure of pigs to tethered housing may lead to development of stereotypies and persisting disturbances in the hormonal, cardiovascular, and immune systems. Von Borell and Ladewig showed that growth rate was reduced in tethered sows as compared with loose housed sows, despite the fact that both groups had similar food intake. This reduction in growth rate indicates disturbed body function, possibly caused by stress related catabolic processes.As described previously, we also found that chronic stress leads to an increase in the impact of endogenous opioid systems that mitigate HPA responses to additional acute stressors. Besides analgesic effects, activation of endogenous opioid systems may have a broader adaptive function. It has been demonstrated that rats which can turn off shock stimulation show no opioid activation, whereas yoked animals, which experience the same electric shock without being able to control its offset, give evidence of stress-activated opioids. These data indicate that not the physically painful stimulation per se, but rather the psychological stress of its uncontrollability seems to be the key factor in opioid activation. By blunting the aversive impact of stressors, endogenous opioids enable the individual to deal more effectively with distressing environmental events. This contention is in line with the idea that stereotypies, displayed when loss of control is experienced and associated with activation of opioid systems, may serve a de-arousal purpose. Schouten et al, showed that the feeding-induced cardiovascular response is decreased and shortened in tethered pigs performing stereotypies, and that this effect is opioid-dependent. The adaptive alterations in opioid systems in tethered pigs may thus be a means of coping with the chronic stress conditions, thereby preventing excessive stress responses (e.g., of the hormonal and cardiovascular systems). However, all of the above mentioned adaptations in behavioural and physiological performance have to be recognized as symptoms of chronic stress. Therefore, they indicate that welfare and health of tethered pigs are compromised.Concluding RemarksThe experiments described in this thesis provide evidence that long-term tethered housing of female pigs induces adaptive changes in adrenocortical function and in activity of endogenous opioid systems. Important in this respect is the finding that loss of control and predictability by factors, such as lack of (visual) information and restriction of social contact, play an important role in the development of these changes. It should be kept in mind, that the adaptive behavioural and physiological changes, observed in tethered pigs, are in fact the symptoms of their "struggle" in order to withstand the environmental demands, and thus indicate compromised welfare. Some of these changes may lead to increased vulnerability of the animals for diseases. Therefore, it is likely that the stress of tethered housing contributes to the high incidence of health problems observed in tethered sows.

IntroductionThe main aspect of this thesis is individual behavioural variation. Behavioural variability among individuals within a population may provide information on strategies or roles in social behaviour, on personality traits and individual recognition. Generally, this behavioural variability becomes overt in stressful situations. Recent data have shown the existence of basically two different coping strategies, active or passive. These different coping styles resemble the two (classical) behavioural stress responses, fight-flight vs. conservation-withdrawal, each with its own characteristic biological pattern. The success of the individual coping response depends on the environmental conditions and, therefore, it is highly surprising that each individual appears to be prediposed to one or the other coping strategy. This suggests a genetic or ontogenetic basis, but recent life experiences will have a significant role also. The idiosyncratic response pattern to a challenge has been shown in many species (humans; monkeys; dogs; tree shrews; etcetera), and hence it may be postulated that this also holds for pigs. If so, these individual behavioural characteristics will have important practical implications in understanding the social relations among group-housed pigs in intensive farm conditions. A stable social structure in the group, and thus a proper group composition, may be a function of the individual behavioural characteristics of each group member. However, until now little research has been conducted to reveal possible patterns underlying a proper group composition in pigs, and subsequently how such mechanisms could be applied in intensive pig husbandry. The present study aims at these aspects.Social statusIn chapter 1, the individual variation in disease susceptibility and immune reactivity of pigs is described in relation to their individual social status in a stable social group. This social status was determined by the outcome of social ranking fights and food competition tests. There was a substantial agreement between the social status determined by these ranking fights and food competition tests. Since these tests were made at quite different ages (respectively; during the suckling period, and on day 50, on day 65, and on day 100), this indicates a relatively stable social structure in the group. At an age of approximately ten weeks, all pigs were challenged intranasally with an Aujeszky virus. Mortality and morbidity were highest among subordinate pigs compared to subdominant and dominant ones. A specific lymphocyte stimulation test, using purified Apjeszky virus as an antigenic stimulus, showed that the cell-mediated immunity (CMI) against the Aujeszky virus was higher for the dominant pigs than for the subdominant and subordinate ones.These findings showed that there were large individual differences in immune reactivity and disease susceptibility in pigs partly related to their individual social status in the group. However, social behaviour of an animal that lives in a social organization is also determined by its individual way of handling stressful situations i.e., its coping strategy. Therefore, the individual coping response may well be another basis for different internal biological programs, which may eventually lead to individual differences in disease susceptibility. In chapter 2 the hypothesis was tested whether consistent individual behavioural characteristics in pigs exist.Individual behavioural characteristicsDuring the suckling period, piglets were classified as aggressive or as non-aggressive individuals in two successive social confrontation (SC) tests by two observers. Substantial agreement in this classification existed between observers and between both SC tests. Moreover, the aggressive behavioural elements observed after mixing at 10 and again at 15 weeks of age were mainly shown by pigs that were classified as the aggressive ones in the two social confrontation tests shortly after birth; this indicates that the behavioural response pattern of the individuals remained consistent over a long period of time. In a non-social backtest piglets were restrained in a supine position for sixty seconds, and classified as resistant (R;>two escape attempts), intermediate Q; = two escape attempts), or as non-resistant (NR; < two escape attempts). Based upon the outcome of five successive backtests piglets were eventually classified as R (n=95), as NR (n=77), or as Doubtful (n=46). Results showed that two backtests performed on piglets at an early age may suffice for practical use. A striking finding was the good association that existed between the outcome of the backtests and of the SC test. The individuals that resisted in the backtests were the aggressive ones in a social situation, while the non-resistant individuals were the non-aggressive ones. This association and the strong consistency over time strongly suggests an individual behavioural strategy to cope with conflict situations. The idiosyncratic characteristics indicate a bimodal distribution in coping behaviour in pigs; they are active (aggressive and resistant; A/R) or passive (non-aggressive and non-resistant; NA/NR) pigs.Individual physiological characteristicsThe way these individual behavioural strategies in pigs relate to different behavioural, physiological, and endocrine responses under stress conditions is illustrated in chapter 3. For this, 32 A/R and 32 NA/NR pigs were selected and individually tested in an open field (OF) test at three and eight weeks of age. While A/R pigs more than NA/NR ones tried to escape the OF, the A/R pigs vocalized less during the OF procedure than the NA/NR ones did. Furthermore, the A/R ones explored a novel object inside the OF rapidly and superficially, whereas the NA/NR ones did so gradually but more intensively. The cortisol response to the OF (t=0/t=90) differed between the A/R and the NA/NR pigs. The cortisol response to a farmacological dosis ACTH 1-39 (2.5 IU/kg live weight/pig) at three and eight weeks of age showed no significant differences between both types of pigs. Nonetheless, the basal cortisol levels were consistently higher for NA/NR pigs than for A/R ones, and this was eventually accompanied by adrenal hypertrophy in the former. The mean heart rate (HR) in beats/min (bpm) was higher of the A/R pigs compared to the NA/NR ones in two backtests. Moreover, in reaction to the novel object (a falling bucket) in the (second) OF HR of the A/R pigs substantially increased (23.9 bpm = 15.5%), while HR of the NA/NR pigs only slightly increased (4.5 bpm = 2.9%). Surprisingly, one-third of the NA/NR individuals even showed a HR decrease (bradycardia) in response to the falling bucket. This implies that the active pigs (A/R) reacted predominantly with a sympathetic response, and the passive pigs (NA/NR) with a parasympathetic one; these findings strongly parallel data found in other animals and humans. The sympathetic response of the active pigs resulted in heart deviations. Thus, active and passive pigs displayed consistent individual differences in behavioural, physiological, and endocrine responses to stress situations leading to different stress pathologies.Individual immunological characteristicsChapter 4 reports about individual differences in cell-mediated and humoral immunity as related to different coping styles in pigs. The immune reactivity of 32 A/R and 32 NA/NR pigs was tested in relation to stress using several cell-mediated (CMI) and humoral immunological tests. Results indicated that the active pigs had a higher in vivo and in vitro CMI to non-specific and specific antigens than the passive pigs. Furthermore, in reaction to stressors applied in the present study (i.e., weaning, new environment, transportation, mixing) active pigs had a reduced but temporary CMI response in the first phase of stress, while passive pigs showed a more chronic impairment. In contrast, the passive pigs displayed higher levels of specific antibodies than the active ones. This suggests a converse relationship in the individual pig between CMI and humoral immunity, in that active pigs had a high CMI but a low humoral immunity, whereas passive pigs had a low CMI but a high humoral immunity. This converse relationship may be associated with different levels of glucocorticoids as described in chapter 3. In conclusion, active and passive pigs clearly differed in their immune reactivity to stressful situations.Practical implicationsHow far group composition based on the individual coping characteristics may influence the growing up of fattening pigs was tested at a commercial closed farm (cf. chapter 5). During the suckling period, piglets of this farm were individually tested in two successive backtests, and classified as R, NR, or as D. At nine weeks of age, the pigs were grouped into six pens with only R pigs (R pens), six pens with only NR pigs (NR pens), and six pens with both R and NR ones (R/NR pens). The average daily weight gain (ADWG; grams/day) was highest of the pigs in the R/NR pens compared to the pigs in the R pens and in the NR pens. Moreover, the coefficient of variation of A~ was lower among R/NR pens than among R pens or NR pens. The carcass weight and meat% was somewhat higher and carcass classification was better of the pigs in the R/NR pens than the pigs in the R pens and in the NR pens. Additionally, pigs in the R/NR pens had less pleurisy than the pigs in the other pens, whereas the number of pigs with stomach wall damage was highest for pigs in the NR pens. Groups consisting of both active (R pigs) and passive (NR pigs) individuals seem to better fit each other than groups with only active or with only passive ones and, thus it is worthwhile to compose groups of pigs based on their individual behavioural characteristics. In practice, good management implies besides perfect climatic and feeding conditions also attention for and understanding of the social environment of the farm animals.General DiscussionIn the general discussion three major topics are discussed: 1) do the behavioural differences in pigs represent idiosyncratic response patterns; 2) do the individual behavioural characteristics in pigs relate to different autonomic nervous and immune reactivity under stress conditions and 3) the relevance of applying behavioural studies in pigs in practice. Especially the intriguing finding that under stressful conditions active and passive pigs need each other to develop a stable social organization needs further research.