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In this paper, the general process of health management and disease prevention at the herd level is described. The important steps include data collection, calculation of performance parameters, decision making, data analysis, problem definition, and finally installing preventive and therapeutic measures. Important components of a successful health management program include reliable data collection, automated data analysis, excellent veterinary clinical skills, and knowledge of epidemiological methods.

As no systematic study has been done to get an accurate estimate of the incidence of return to oestrus after first insemination in sows in the Netherlands, the objectives of this investigation were: 1) to obtain an estimate of the incidence of return to oestrus after insemination at the herd level; 2) to investigate the association between incidence of return to oestrus after first insemination and reproduction characteristics to get an impression of the economic importance. These objectives were investigated using the reproduction results of 240 swine breeding herds in The Southern Netherlands in 1987, using their CBK plus computerized herd management records. The average incidence of return to oestrus after first insemination on a herd level was 16.9 per 100 first inseminations. An increase of incidence with 10 returns per 100 first inseminations, corrected for confounders in a multiple linear regression model, was associated with a decrease of approximately 0.3 liveborn piglets/sow/year. Thereupon individual sows were followed in 1988 and 1989 prospectively in 37 sow herds from weaning to insemination, returning to oestrus or not after first insemination to farrowing. The investigation focused in particular on the relationship between returning to oestrus after first insemination and incident infection with porcine parvovirus (PPV) and Leptospira interrogans serovar bratislava (L. bratislava). During a number of consecutive farm visits sows were blood sampled at weaning and again a blood sample was taken 6 weeks later. The final dataset that was analysed consisted of 161 animals that did not return to oestrus after first insemination and 158 animals that returned to oestrus after first insemination.(ABSTRACT TRUNCATED AT 250 WORDS)

The severity of experimental Escherichia coli mastitis in relation to in vitro chemotaxis of polymorphonuclear leukocytes was investigated in cows during negative energy balance. The negative energy balance was induced by feed restriction. Cows were classified into two groups, ketonemic and nonketonemic, based on the beta-hydroxybutyrate concentration in the peripheral blood at the moment of inoculation. Bacterial growth in the inoculated quarter was used as a parameter to indicate the severity of experimental mastitis. In the nonketonemic cows, experimental mastitis ranged from moderate to severe. Severity of experimental mastitis was negatively related to preinfection chemotactic response of polymorphonuclear leukocytes. In contrast, the course of experimental mastitis in the ketonemic group was relatively severe in all cows, regardless of preinfection chemotactic response.

The objective of the study was to evaluate the effect of administration of antibiotics to cows at dry-off in a low SCC herd. Cows were infused at dry-off with an intramammary antibiotic on the left or the right side of the udder. Selection of the infused quarters was random, and all people evaluating the occurrence of mastitis were unaware of which half of the udder was infused. The quarters that were infused with an antibiotic showed a significantly lower incidence of clinical mastitis in the dry period. Quarters that were uninfused had 10 cases of clinical mastitis versus 1 case in quarters that were infused with antibiotics. The quarters that were infused showed a reduction of minor pathogens at calving. The uninfused quarters showed little evidence of spontaneous cure during the dry period. Milk leaking was frequent during the drying off period. Milk leaking was also associated with the occurrence of clinical mastitis later in the dry period. Cows that leaked milk had a four times greater risk of clinical mastitis in the dry period.

To study the relation between on-line electrical conductivity and daily milk production, data of 1389 cow days were analyzed. After correction for cow effects and DIM, a rise of 1 mS of the mean electrical conductivity caused a decline of .88 kg/d in milk production. A rise of 1 ln(SCC) unit was associated with an additional decline of .54 kg/d in milk production. In cows without clinical mastitis during the test period, the losses associated with mean electrical conductivity and ln(SCC) were 1.06 and .45 kg/d of milk production, respectively. Electrical conductivity and SCC were associated with daily production loss; the effects were additive. Therefore, electrical conductivity and SCC can be utilized as indirect tests of subclinical mastitis.

Somatic cell count (SCC) in milk is inversely related to dairy cow productivity and milk quality. In an effort to improve product quality, and indirectly farm productivity, regulatory limits on somatic cell counts have been established by many of the major dairy producing countries. The purpose of this paper was to assess the impact of regulations on bulk milk somatic cell counts in Ontario and to assist producers in meeting regulatory limits through development of prediction models. Through the use of a transfer function model, provincial SCC was found to have dropped by approximately 60,000 as a result of the reduction program. Limits of the regulatory program, seasonality and herd characteristics were found through time series cross-sectional models to have an impact on prediction of SCC at the farm level, but the major influence was historical SCC levels.

In a set of data on farmer-observed clinical mastitis in cattle, all milk samples were scored with regard to milk color and milk texture (presence of flakes and viscosity). During a 1-year period, 1,106 milk samples were collected from 125 farms with a bulk milk somatic cell count < 150,000 cells/ml. The overall variation, the between-herd variation, and the within-herd variation of the scores were evaluated and compared with each other. Differences between farmers were found for the scores on the visual characteristics per sample. However, these differences were not related to the reported number of cases of clinical mastitis per year. It was concluded that the diagnostic capability of farmers whose herds had low somatic cell counts did not have a negative influence on the validity of farmer-observed clinical mastitis incidence. However, care should be taken in herds with a low frequency of cases.

The diagnoses Porcine Epidemic Abortion and Respiratory Syndrome (PEARS)-positive and PEARS-negative can be made using the following data on herd performance: the average number of stillborn piglets per litter, the average number of live piglets per litter and the average piglet mortality before weaning. Depending on the number of litters used in calculating the averages, the extent to which two out of the three performance data should deviate to arrive at the diagnosis PEARS-positive is given in tables and figures. The same farm will only be diagnosed PEARS-negative if after some time at least two out of the three performance data deviate less than other criteria also provided in tables and figures.

To determine the additional costs and returns of twin calvings in dairy cattle, an economic model was developed on the personal computer. Data used in the model were recorded on 33 farms over 6.5 yr and included 381 twin calvings. For missing information, assumptions were made from the literature. Additional calf returns turned out to be $2.96. Total additional cost were $71.47, consisting of $100.92 for milk reduction, $39.51 for increased premature culling, $19.25 for increased occurrence of abortion, $5.69 for increased therapy, and $6.09 for increased calving interval. Total losses were on average $171.47 - $62.69 = $108.51 per twin birth. Realistic changes in input variables could not change this negative outcome to a positive result. Therefore, it was concluded that it is not profitable to select to increase the number of twins in dairy cattle.

The physics, physiology, and pathology of electrical conductivity of milk are described. Based on a meta analysis, the use of electrical conductivity as a mastitis detection tool is discussed. Most reports were based on subclinical mastitis data. The gold standards of the different reports are discussed. With an overall sensitivity of 66% and an overall specificity of 94%, the predictive value of a positive electrical conductivity test remains low in a low prevalence population. The use of on-line systems for clinical mastitis detection is discussed. On-line systems that combine multiple data and perform multifactorial analyses will be of interest to the dairy industry.

An epidemiologic survey was performed to determine the incidence of torovirus infections in 2 disease entities of cattle: diarrhea of replacement calves up to 2 months old, and winter dysentery of adult cattle. Samples were obtained from 187 diarrheal and 115 healthy calves from 15 farms, as well as 149 diarrheal and 67 healthy cows from 27 farms with or without winter dysentery. Enzyme-linked immunosorbent assays for detection of torovirus, rotavirus, and coronavirus antigen in feces, and of torovirus and coronavirus antibodies in serum were used to monitor infections in these groups. Torovirus was detected in 9 of the 15 farms in the study, and in 6% of calves with diarrhea, which was significantly higher than in healthy calves (2%). Seroconversion to torovirus was found significantly more often after winter dysentery episodes than on farms without a disease history; coronavirus seroconversion was less common.

The incidence rate of clinical mastitis due to Escherichia coli and Staphylococcus aureus was studied in 125 herds with a low annual bulk milk somatic cell count (less than 150,000 cells/ml). Risk factors that were offered to a multivariate Poisson regression model included general management, housing, cleaning procedures, cow and cubicle cleanliness, feeds and feeding, dry cow management, milking procedures, machine milking, disease prevention, and milk production. Some differences in epidemiology between E. coli and S. aureus were observed. In the S. aureus model, more milking procedure and milking machine variables were present. The milk production, drinking water source, amount of bedding, and ventilation were other important factors in the S. aureus model. Teat disinfection was an important risk factor in the E. coli model but was much less important in the S. aureus model. Cleaning procedures were more important in the E. coli model. The main breed on the farm and percentage of cows leaking milk were other important factors in the E. coli model.

The incidence rate of clinical mastitis in 125 herds with a low annual bulk milk SCC (less than 150,000 cells/ml) was modeled using a Poisson regression model. The rate of clinical mastitis was significantly associated with some variables that increased the exposure to environmental microorganisms: poor cubicle cleanliness increased the mastitis rate; rubber mats in cubicles were associated with a higher incidence; and drinking water from sources other than public water also increased the rate of mastitis. Other variables may be associated with host resistance: an increasing percentage of cows leaking milk increased the rate of mastitis; postmilking teat disinfection was associated with a higher incidence of clinical mastitis; and a high frequency of cubicle disinfection was also associated with more mastitis. Three other variables were associated with the rate of mastitis: breed (Holstein-Friesian had a lower incidence than the Meuse-Rhine-Yssel breed); use of sugar beet pulp in the ration increased the mastitis rate; and in herds with high milk production a higher incidence of mastitis was observed. These items are discussed in respect to their causal relation to clinical mastitis.

The objective of this study was to assess growth of Escherichia coli in milk from endotoxin-induced mastitic quarters and to relate the in vitro findings to the course of experimental E. coli mastitis. Whole and skim milks from 24 rear quarters of 12 cows were inoculated with E. coli 0:157 and incubated at 38 degrees C. Growth of E. coli 0:157 was not inhibited in milk collected from rear quarters immediately prior to endotoxin infusion. However, growth inhibition occurred in all but one whole mastitic milk samples collected from mastitic quarters 18 h after infusion of .1 mg of endotoxin. Skim milk samples from mastitic quarters were bactericidal in four cows (7 quarters), whereas growth occurred in skim mastitic milk from 17 quarters of nine cows. Rear quarters of all cows were inoculated with 10(4) cfu of E. coli 0:157 19 h after the quarters had been infused with endotoxin. Clinical parameters and milk production were monitored during 36 h and 21 d, respectively. None of the inoculated quarters developed signs of inflammation, and secreta from inoculated quarters were bacteriologically negative after 48 h. Therefore, growth-inhibitory property of skim milk from endotoxin-induced quarters was apparently not a suitable parameter to monitor differences in susceptibility to E. coli mastitis.

The population dynamics for bulk milk SCC in 27,000 Dutch dairy farms was studied over 6 yr; SCC declined markedly in 1984 and 1985. This coincided with the introduction of the quota system in the European Community. The CV of SCC was .36, ranging from .15 to .89. Month of year had a significant effect on SCC with the highest SCC in October and the lowest in April. The dynamics of the annual SCC were modeled with a state transition model. Farmers managing herds with a fairly low SCC (less than 450,000) had a reasonable chance to remain in these states. Herds with a higher annual SCC were much more variable. The model simulated, the potential reactions of the farmers to the decrease of the SCC limit from 750,000 to 500,000 starting January 1, 1989. The simulations showed a further decrease in mean annual SCC, although the number of farms in the category with a very low SCC (less than 150,000) is not likely to increase. In all simulations an increased number of farmers will receive a penalty due to the more strict regulations of the European Community.

The relationship between preinfection functions of blood neutrophils and outcome of experimental Escherichia coli mastitis was studied in 11 cows. Random migration, chemotaxis, phagocytosis, and chemiluminescence by neutrophils were determined in white blood cell suspensions, and in purified neutrophil suspensions. The course of E. coli mastitis (10(4) E. coli 0:157 in rear quarters) was monitored using clinical parameters, counts of E. coli in mastitic secretion, and milk production. Regressions were calculated for areas under curves of these parameters and preinfection activities of neutrophils. Chemiluminescence by nonstimulated neutrophils in white blood cell suspensions was negatively correlated with counts of E. coli in secretion and with losses in milk production. The chemotactic differential in white blood cell suspensions minus the chemotactic differential in purified suspensions of neutrophils referred to as delta varied from -.66 to +.50, indicating, respectively, inhibition and stimulation of chemotactic activity of neutrophils in white blood cell suspensions. Delta correlated negatively with counts of E. coli in mastitis secretion, inhibition of the amplitude of rumen contractions, and losses in milk production. We hypothesize that a factor in white blood cell suspensions may be involved in the down-regulation of the migratory response of neutrophils during E. coli mastitis.

The objectives were to describe the systemic signs during the acute phase of experimental Escherichia coli mastitis and to relate these with losses in milk production during the reconvalescent period. Eleven cows, 20 to 30 d postpartum, were inoculated with 10(4) cfu of E. coli O157 in rear quarters. Heart rate, rectal temperature, frequency and amplitude of rumen contractions, plasma Zn and Fe concentrations, and counts of E. coli were used to monitor severity of disease during the acute phase. Areas under curves of clinical parameters, plasma Zn and Fe concentrations, and counts of E. coli were calculated during 36, 120, and 125 h postinoculation, respectively. Areas under curves of milk production were calculated during 21 d postinoculation. Losses in total daily milk production were related positively with areas under curves of heart rate, rumen amplitude, counts of E. coli in secreta from inoculated quarters, and plasma Zn and Fe concentrations. These parameters may prove suitable to establish an accurate prognosis for returning to milk production cows suffering from acute or peracute E. coli mastitis and to evaluate efficacy of drugs in experimental mastitis.

Ten herds with low somatic cell counts in bulk milk had an incidence of clinical mastitis of only 2.2 per 100 cows whereas 10 other herds with similarly low cell counts had an incidence of 53.6 per 100 cows. The major pathogens in the herds with a high incidence were Escherichia coli, Streptococcus uberis, Staphylococcus aureus and the coagulase-negative staphylococci. The percentage of uninfected quarters in the herds with a high incidence of clinical mastitis was 21.4 per cent compared with 12.2 per cent in the herds with a low incidence of clinical mastitis. The prevalence of coagulase-negative staphylococci, Corynebacterium bovis and Micrococcus species was higher in the herds with a low incidence of clinical mastitis. There was a significant linear relationship between the percentage of uninfected quarters and the incidence of clinical mastitis in the herds with a high incidence of clinical mastitis. In herds with a low incidence of clinical mastitis significantly less teat disinfection after milking was practised. The results suggest that infections with minor pathogens tend to protect cows against mastitis, and that teat disinfection after milking may increase the percentage of uninfected quarters and lead to an increased risk of clinical mastitis in herds with low somatic cell counts in bulk milk.

A total of 1140 clinical cases of mastitis, with at least one inflamed quarter, were reported on 125 farms with somatic cell counts in bulk milk less than 150,000/ml. The average annual incidence was 17.9 cases per 100 cows and ranged from none to 80 cases per 100 cows. The microorganisms most frequently isolated were Escherichia coli (16.2 per cent), coagulase negative staphylococci (13.0 per cent), Staphylococcus aureus (9.6 per cent) and Streptococcus uberis (8.0 per cent). Only two cases of Streptococcus agalactiae were found. As the incidence of clinical mastitis increased, the proportion of S aureus also increased, while the proportions of E coli, S uberis and Streptococcus dysgalactiae remained about the same. Most of the clinical cases of mastitis occurred in early lactation, in November, December and January. However, after correction for the number of calvings per month, the incidence of mastitis was highest in the early summer months.

This review paper is concerned with antibacterial therapy of mastitis caused by Escherichia coli. The choice of an antibacterial agent is discussed, and nine criteria are referred to, on which this choice should be based. In the second part possible forms of antibacterial treatment are discussed. Literature on parenteral and local treatment of mastitis due to E. coli is scarcely available. The evaluation of antibacterial drugs is mainly based on MIC values and pharmacokinetic studies in normal animals. Unfortunately, results of clinical trials are hardly available. Today combinations of trimethoprim/sulphonamide apparently are the best available choice for the parenteral treatment of mastitis caused by E. coli. Infusion of polymyxins or gentamycin is discussed as a method of intramammary therapy.

The pathogenesis, course run by the disease, and symptomatic treatment of mastitis due to Escherichia coli in dairy cattle are reviewed in relation to the functioning of cellular and humoral defence mechanisms. The systemic symptoms of disease during mastitis caused by E. coli are attributed to the release and subsequent absorption from the udder of endogenous inflammatory mediators, rather than the direct absorption of endotoxins into the circulation. The course run by the disease during mastitis due to E. coli varies considerably. Reasons for these variations include genetic variation, stage of lactation and the function of humoral and cellular defence mechanisms.

The technique of epidural anaesthesia is described in the present paper. In addition, the relationship between external features and the dosage of the local anaesthetic was studied. In this study, epidurography was used to visualise the cranial extension of the anaesthetic solution in the vertebral canal. It is concluded that the most reliable parameter is the length of the spinal column. Cases in which the use of epidural anaesthesia is indicated, are stated.

Treatment of a lesion of the teats not associated with perforation of the teat canal or teat cistern is discussed in the present paper. Treatment of the lesion of the teats using a Bykanula is compared with temporary drying off of the involved quarter. In eleven out of the twenty cases reported, the process of healing was complicated by mastitis in the involved quarter. When the outlet of the teat was involved in the lesion, this complication was likely to be 5.4 times larger than it was when the teat opening was not involved. In the 'temporary drying-off group', the complicating mastitis was a reason for culling the animal within six months after treatment had been initiated in five out of nine cases. On the other hand treatment of the complicating mastitis in the 'Bykanula-group' was successful in every case. Problems in carrying out this clinical trial are also discussed.

In a retrospective study, the risk for cardiac dysrhythmias was evaluated in dogs undergoing ventral decompression and/or fenestration of the cervical spine (CERV) and compared with that for dogs undergoing dorsal laminectomy for decompression of the thoracic or lumbar spine (TL). The dogs in the CERV subset (48 dogs) tended to be heavier and older than the dogs in the TL subset (111 dogs). There was no apparent bias detected in treatment before anesthesia and surgery. The risk for dysrhythmias was 2.5 times greater in the CERV subset, compared with that in the TL subset (P less than 0.01). The risk for ventricular premature contraction was 3.5 times higher in the CERV group (P less than 0.05). Bradycardia was found in 6 dogs from the CERV subset and was not found in any dogs from the TL subset. A logistic model was derived from the data and may be used to evaluate the risk for dysrhythmias in similar patients undergoing similar surgery and anesthesia. This model uses age, preoperative heart rate, and site of surgery (CERV or TL) to estimate the risk.

We used two statistical techniques for space-time cluster analysis, the Knox and the Mantel regression methods, for an analysis of whether herd outbreaks of farmer-diagnosed winter dysentery during the winter of 1987-1988 were clustered in space and time more than would be expected by chance. Using the Knox method, there was significant space-time clustering of outbreaks of winter dysentery within a 30 day time and a 5.5 km radius. There was also significant space-time clustering by the Mantel regression method.Logistic regression was used to study risk factors for herd outbreaks of winter dysentery. Large herds (>60 cows) and herds with a history of an outbreak prior to 1987 had increased chances of an outbreak occurring in 1987-1988.These results are compatible with an infectious cause for winter dysentery.

The diagnostic aspects, incidence, risk factors and prevention of coliform mastitis are reviewed in the present paper. It is concluded that it is not possible to establish an accurate diagnosis of coliform mastitis, which is based on a specific clinical symptom differentiating it from other forms of mastitis. Not any single symptom or combination of symptoms is specific for coliform mastitis. The importance of coliform mastitis in dairy cattle showed a marked increase during the last few decades. Successful programmes for the prevention of mastitis reduced the importance of contagious organisms, but the overall incidence of mastitis has remained unchanged; therefore, the proportion of cases of coliform mastitis increased. The observation that coliform micro-organisms are common bacteria causing mastitis in herds with low bulk milk somatic cell counts implies that the future of the dairy industry will be associated with particular risks. Factors involving the risk of coliform mastitis are divided into cow level factors and herd level factors. The most important cow level factors were: leaking milk in between milkings, lesions of the teats and a reduced capacity of the immune system. Risk factors on the herd level include: the bedding material, the design of cubicles, exposure to daylight in summer-time, exposure to dirt and the use of dry-cow therapy. The possible role of antibiotic dry-cow treatment and teat dipping in colonisation resistance is discussed. Preventive programmes designed to reduce the incidence of coliform mastitis have not been very successful so far.

An index was developed to measure the proportion of intramammary infections caused by environmental microorganisms on dairy farms. This environmental index can be interpreted as the probability that an intramammary infection was caused by an environmental pathogen, rather than by a contagious pathogen. Using the environmental index as the outcome variable, risk factors for environmental mastitis were studied on 10 dairy farms in New York. Turning the cows outside was associated with lower environmental index, and having cows drink from a stream increased the environmental index. Selective (rather than uniform) nonlactating cow intramammary treatment was related to a lower environmental index (apparently because the farms practicing selective nonlactating cow treatment suffered from epizootics of contagious mastitis).

Twin calvings on Dutch dairy farms were studied using data collected through a routine herd health and production management program. Over a period of 6.5 yr, 381 twin calvings (762 calves) of a total of 11,951 calvings were recorded on 33 farms. The 381 twin calvings were compared with a referent group of 1,536 calvings that was randomly selected from the orginal 11,951 calvings. Risk factors for twin calvings were parity, season, herd and previous twinning. High cumulative milk production was associated with cows conceiving twins. Treatment for infertility in the preceding lactation was an equivocal risk factor. Twin calvings increased the risk of abortion, retained placenta, fertility-related treatment, as well as the number of days open and the number of inseminations per conception. Although twin calvings resulted in more calves born per dam, the number of available replacement heifers did not increase. After twin calving, cows produced slightly less milk and were culled more often than single calving cows. To adapt appropriate management practices for cows carrying twins, an early and reliable method for detecting twin pregnancies is needed.

We investigated the relation between retained placenta and mastitis in Holstein dairy cows admitted to the New York State College of Veterinary Medicine. Cows with retained placenta were three times more likely to develop mastitis during hospitalization than animals without retained placenta. Since the hospital population was not representative of the general population, the possibility of a bias existed; a large bias was not likely because most distorting variables occurred equally in animals both with and without retained placenta. The literature suggests that the relationship between retained placenta and mastitis may be mediated through activity of the peripheral leukocytes. Further research is necessary to test this hypothesis.

The objective was to determine the effect of freezing and length of freezing in a commercial freezer on the qualitative results of bacteriologic culturing of milk collected from glands of cows with clinical or subclinical intramammary infections. A total of 182 milk samples from cows with clinical mastitis and 55 milk samples of cows with subclinical mastitis were taken from four problem herds. Samples were split into four equal sub-samples. Three of these were frozen immediately at -20 degrees C and 1 was submitted fresh for bacteriologic analysis. At 4, 8, and 16 wk after collection, samples were thawed and submitted for bacteriologic culturing. Freezing and increased length of storage resulted in 1) a decrease in the number of samples that had cultures of Escherichia coli or Actinomyces pyogenes; and 2) an increase in the number of samples that had cultures of coagulase-negative staphylococci. Freezing had no effect on streptococci and Staphylococcus aureus.