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Context Nutritive values, particularly energy content of tropical forages, need to be accurately assessed so that rations can be more precisely formulated. Aims The research aimed to collate and compare equations used to predict metabolisable energy content in forage sorghum (Sorghum bicolor (L.) Moench) to ascertain the effect of vertical strata on metabolisable energy content to assist in producing silage of defined quality. Methods Twenty-four predictive metabolisable energy equations derived from international feeding standards were compared using forage sorghum samples grown under fertiliser and growth stage treatments. Samples were separated into leaf, stem and seed heads (where present) over four vertical strata. Key results Equations based on digestibility with crude protein were robust in the prediction of metabolisable energy and had application to routine laboratory use. Conclusions The current study suggests that predictions based on digestibility and crude protein content are best placed for metabolisable energy application. Such equations should be originally based on measured metabolisable energy content to establish a regression so as to be used for predictive purposes, and satisfy the biological requirement of in vivo and the laboratory measurement relationship with acceptable statistical error. Chemical composition relationships predicted different metabolisable energy contents. Implications Improved accuracy of the prediction of metabolisable energy content in tropical forages will provide better application of production models and more accurate decisions in ration formulation.

A plot study was conducted at the Gatton Research Dairy, Queensland, Australia, to quantify the effects of 5 regrowth periods (9, 11, 14, 16 and 18 days) and 4 vertical strata on the composition and nutritive value of kikuyu (Cenchrus clandestinus) pastures using a block factorial design with 4 replicates. Pasture samples were analyzed for crude protein (CP), ethanol-soluble carbohydrates (ESC), acid detergent fiber (ADF), neutral detergent fiber (aNDFom), in vitro indigestible neutral detergent fibre (iNDF240) and minerals. Metabolizable energy (ME) was then calculated from the concentrations of other nutrients. Regardless of the stage of regrowth, stems were located mainly in the bottom 1 or 2 strata, while leaves were present mainly in the top 2 or 3 strata. CP, ESC and ME declined, but aNDFom, ADF and iNDF240 increased with stage of regrowth and from top to bottom of the swards (P

An understanding of the processes involved in grazing behaviour is a prerequisite for the design of efficient grassland management systems. The purpose of managing the grazing process is to identify sward structures that can maximize animal forage daily intake and optimize grazing time. Our aim was to evaluate the effect of different grazing management strategies on foraging behaviour and herbage intake by sheep grazing Italian ryegrass under rotational stocking. The experiment was carried out in 2015 in southern Brazil. The experimental design was a randomized complete block with two grazing management strategies and four replicates. The grazing management treatments were a traditional rotational stocking (RT), with pre- and post-grazing sward heights of 25 and 5 cm, respectively, and a ‘Rotatinuous’ stocking (RN) with pre- and post-grazing sward heights of 18 and 11 cm, respectively. Male sheep with an average live weight of 32 ± 2.3 kg were used. As intended, the pre- and post-grazing sward heights were according to the treatments. The pre-grazing leaf/stem ratio of the Italian ryegrass pasture did not differ between treatments (P > 0.05) (~2.87), but the post-grazing leaf/stem ratio was greater (P < 0.001) in the RN than in the RT treatment (1.59 and 0.76, respectively). The percentage of the non-grazed area was greater (P < 0.01) in post-grazing for RN compared with RT treatment, with an average of 29.7% and 3.49%, respectively. Herbage nutritive value was greater for the RN than for the RT treatment, with greater CP and lower ADF and NDF contents. The total time spent grazing, ruminating and resting did not differ between treatments (P > 0.05), with averages of 439, 167 and 85 min, respectively. The bite rate, feeding stations per min and steps per min by sheep were greater (P < 0.05) in the RN than in the RT treatment. The grazing time per hour and the bite rate were greater (P < 0.05) in the afternoon than in the morning in both treatments. The daily herbage intake by sheep grazing Italian ryegrass was greater (P < 0.05) in the RN than in the RT treatment (843.7 and 707.8 g organic matter/sheep, respectively). Our study supports the idea that even though the grazing time was not affected by the grazing management strategies when the animal behaviour responses drive management targets, such as in ‘Rotatinuous’ stocking, the sheep herbage intake is maximized, and the grazing time is optimized.

Pasture meters are typically calibrated to estimate total pasture mass (TPM). Recent studies have shown that animal productivity was driven by the level of utilisation of the top leafy stratum (TLS) rather than the TPM. A study of kikuyu (Pennisetum clandestinum) pasture conducted on two farms located in southeast Queensland, Australia assessed whether pasture mass of the TLS, bottom stemmy stratum (BSS) and TPM can be more accurately estimated by using not only pasture surface height but also pasture density derived from height data captured by a laser sensor. The results indicated that there was a notable improvement of the pasture mass estimates when density was included in the calibration equations. The study also compared the accuracy of the pasture mass estimates between the laser sensor and mechanical pasture meters (rising plate meter and ruler). The results indicated that all devices provided reasonable estimates of pasture mass for TLS, BSS and total (R2 ≥ 0.75). However, pasture mass was estimated with a slightly higher level of accuracy when using the laser sensor in comparison with the other pasture meters, particularly for the top leafy stratum (R2 = 0.81 vs R2 ≤ 0.77).

SUMMARYSugarcane is an important forage resource in sub-tropical and tropical areas as it is used during the winter or dry season when the growth rate of pastures is significantly reduced. The current research study assessed the effect of four vertical sections of sugarcane in a pen trial and the level of sugarcane utilization in a grazing trial on the ingestive behaviour and forage intake of two age groups of steers (1 and 2 years old). The pen trial was comprised of two simultaneous 4 × 4 balanced Latin square designs (one for each age group of animals) of four periods, four animals and four feeding treatments, which consisted of four equal vertical sections of sugarcane. Dry matter (DM) and digestible DM (DDM) intake per kilogram of metabolic weight declined gradually from top to bottom of the sugarcane, with no significant differences between the age groups of steers. This difference in intake was associated with a decline in intake of neutral detergent fibre (NDF) as a proportion of the liveweight of the animal and an increase of total chewing time per kilogram of DM or NDF from top to bottom of the sugarcane. It was concluded that the toughness of plant material played a significant role regulating intake, which was higher for the top sections of sugarcane. In the grazing trial, steers of both age groups grazed down sugarcane in three plots over 9 days. Steers grazed up to four distinctive grazing strata. Digestible DM intake (DDM intake) was high at low levels of horizontal utilization of the top grazing stratum but DDM intake started to decline sharply when this stratum was removed in 0·92 of paddock area (i.e. equivalent to 0·08 of the pasture area remaining un-grazed). It was concluded that the proportion of un-grazed area of the pasture can be used as a grazing management strategy to control forage intake for sugarcane.

‘Rotatinuous’ stocking is a grazing management strategy based on animal behavioural responses to sward structure which is designed to maximize herbage intake per unit of grazing time. It is an alternative to traditional grazing management practices focusing on pasture use efficiency and maximizing herbage accumulation and harvesting. To investigate this approach, Italian ryegrass (Lolium multiflorum) pastures grazed by sheep were evaluated in 2014 and 2015 under two contrasting grazing management strategies. Paddocks were distributed under a complete randomized block design with four replicates. Grazing management strategies were: traditional rotational stocking (RT), with pre- and post-grazing sward heights of 25 and 5 cm, respectively, and ‘Rotatinuous’ stocking (RN), with pre- and post-grazing sward heights of 18 and 11 cm, respectively. Thirty-two castrated Texel × Polwarth crossbred lambs were randomly allocated to treatments. As a consequence of grazing strategies, the stocking cycles were 12 and 4, with resting periods of 13 and 35 days, respectively, for RN and RT treatments. Herbage production, total herbage harvested, and feed conversion efficiency were 28%, 20%, and 40%, respectively, greater for RN than for RT treatment. Although the stocking rate was lower, the average daily gain per animal and live weigh gain per hectare were 153% and 43%, respectively, greater for the RN treatment. Despite the RN treatment being orientated to maximize herbage intake per unit of grazing time, it results in greater total herbage production and harvesting. We conclude that the ‘Rotatinuous’ stocking strategy is not necessarily reversed by low herbage harvesting efficiency. This innovation in grazing management conciliates high herbage and animal production at the same time.

Grazing systems represent a significant source of enteric methane (CH), but available techniques for quantifying herd scale emissions are limited. This study explores the capability of an eddy covariance (EC) measurement system for long-term monitoring of CH emissions from grazing cattle. Measurements were made in two pasture settings: in the center of a large grazing paddock, and near a watering point where animals congregated during the day. Cattle positions were monitored through time-lapse images, and this information was used with a Lagrangian stochastic dispersion model to interpret EC fluxes and derive per-animal CH emission rates. Initial grazing paddock measurements were challenged by the rapid movement of cattle across the measurement footprint, but a feed supplement placed upwind of the measurements helped retain animals within the footprint, allowing emission estimates for 20% of the recorded daytime fluxes. At the water point, >50% of the flux measurement periods included cattle emissions. Overall, cattle emissions for the paddock site were higher (253 g CH m adult equivalent [AE] d, SD = 75) and more variable than emissions at the water point (158 g CH AE d, SD = 34). Combining results from both sites gave a CH production of 0.43 g kg body weight, which is in range of other reported emissions from grazing animals. With an understanding of animal behavior to allow the most effective use of tower placement, the combination of an EC measurement platform and a Lagrangian stochastic model could have practical applications for long-term monitoring of fluxes in grazing environments.

This study assessed the use of pasture attributes to control daily intake and diet quality during progressive defoliation on pastures of Axonopus catarinensis. Three consecutive 12-day grazing treatments of progressive defoliation were conducted with Brahman cross-steers. Daily forage intake and defoliation dynamics were assessed using a pasture-based method. The treatments differed in initial sward height (33, 44 and 61 cm) and herbage mass (1030, 1740 and 2240 kg ha−1). The post-grazing residual sward height, at which forage intake decreased, appeared to increase with the initial sward height (12·3, 14·6 and 15·5 cm). Steers grazed up to four distinctive grazing strata in all treatments. The depth and herbage mass content of the top grazing stratum were at least five times higher than the lower grazing strata in all treatments. This explains why forage intake decreased when the top grazing stratum was removed in approximately 93% of the pasture area in all treatments, equivalent to approximately 7% of the pasture area remaining ungrazed. We conclude that the residual ungrazed area of the pasture, rather than residual sward height, can be used to develop grazing management strategies to control forage intake and diet quality in a wide range of pasture conditions.

The effect of lucerne pasture allocation on defoliation dynamics, pasture intake and animal production was investigated in a subtropical partial mixed-ration dairy system. The study took place at the Gatton Research Dairy, south-eastern Queensland, with a 28-day adaptation period followed by an 8-day treatment period during November and December 2016. Twenty-four multiparous Holstein Friesian dairy cows were offered 11 kg of dry matter (DM)/cow.day as partial mixed-ration dairy system, and four levels of daily pasture allocation measured to 5-cm residual pasture height (averaging 30.6, 20.5, 15.1 and 10.9 kg DM/cow.day). Cows with lower allocations were forced to graze further down the vertical plane and pasture intake and milk yield significantly (P < 0.001) declined. Cows grazed the top grazing stratum (TGS) across 80% of the pasture area before re-grazing another area of the paddock, regardless of the allocation level. Pasture intake (kg DM/ha) of the TGS was at least 2.9 times higher than that of the lower strata, regardless of allocation level. Therefore, the decline in pasture intake is explained by the transition from grazing the TGS to grazing lower strata. When the horizontal utilisation of the TGS approached 100%, the proportion of ungrazed, uncontaminated pasture approached 0% of the area, and intake and milk production declined. Grazing management strategies for lucerne should allocate pasture to lactating dairy cows to achieve horizontal utilisations approaching 0% for proportion of ungrazed, uncontaminated pasture to maximise intake and production. Secondary grazing herds or mechanical methods should be used to remove residual pasture to the ideal height for pasture regrowth.

There is an increasing interest in the addition of fibrolytic enzymes to the rumen as a way of improving the utilization of the fibrous components of the diet. However, the mechanisms involved in such effects remain uncertain; direct enzymatic hydrolysis has been suggested, but indirect benefits through a modified rumen environment for cellulolytic bacteria have also been reported. In the work reported here, different carbohydrases and their interactions with ruminal cellulolytic activity were evaluated. Pure substrates for standard activity measurement were carboxymethyl-cellulose, birchwood xylans and citrus pectin; forage samples were alfalfa (Medicago sativa L.), berseem trefoil (Trifolium alexandrinum L.), oat fodder (Avena sativa L.) and annual ryegrass (Lolium multiflorum L.). Eleven commercial products, covering different polysaccharidase activities, were evaluated as single sources of enzymes and further pooled together and their individual activity assessed. The results indicated that no single enzyme could account for the overall fibre breakdown observed with the complete pool of enzymes. When six enzymes were selected according to their contribution towards fibre hydrolysis in the pool, essentially the same activity was observed as when all 11 were present. We concluded that the greatest effect was obtained when a mixture of cellulase, xylanase and pectinase was added, preferentially dosed according to the relative proportions of different polysaccharides in the substrate. Microscopic observations confirmed the hydrolytic capacity of the enzymes used. The incubation medium was modified with citric acid to obtain pH values of 6.8, 6.4, 6.0 and 5.6. The polysaccharidase activity of commercial enzymes was not affected by pH in a microbial free medium but in vitro rumen fluid breakdown was severely depressed as acidity increased. However, when commercial enzymes were added to the rumen fluid, hydrolysis was improved as the medium became more acidic. We concluded that exogenous and microbial enzymes compete for the same substrate.

Detection of a reduction in forage intake is particularly relevant in grazing animals due to its negative effect on animal performance. Estimations of intake reduction using faecal markers can be inaccurate due to the time delay between a change in forage intake and the subsequent change in faecal output. This delay may vary depending on forage quality and marker type. A pen study was conducted for 29 days to test the efficacy of liquid (PEG = polyethylene glycol) and solid (alkanes and CrCl₃ = chromium chloride) phase faecal markers to detect a reduction in intake by steers of diets that varied in forage quality. Ten Brahman cross steers (296 ± 16 kg) were allocated equally to diets of leafy, high quality buffel grass (Cenchrus ciliaris) hay and stemmy, low quality buffel grass hay. Hay was offered ad libitum from day 1 to 7, at 90% of voluntary intake from day 8 to 14 and then reduced by 8% each day from day 15 to 24. On day 5 each steer was dosed with two slow release alkane capsules; also, steers received a single daily dose of PEG and CrCl₃ at 09:00 on days 5-24. Actual and marker derived estimates of forage intake over days 10-22 were assessed by repeated-measures analysis of variance. Overall marker recovery rates were satisfactory (0.92-1.03) and there was a significant (P

This pot study assessed the effects of deferring forage during autumn and leaving as winter cover on reducing cold damage to plants of 2 tropical (C4) grasses (Chloris gayana and Panicum coloratum) in a temperate environment in La Plata, Buenos Aires, Argentina. Mature plants were subjected to the following treatments: (i) autumn-deferred forage retained (DF) as control; and (ii) autumn-deferred forage removed (DFR) cutting at 15 cm from soil level at beginning of winter. This experiment had 10 replicates per treatment and 1 plant per pot (experimental unit). Plants of both species were extracted from a commercial beef farm and transplanted into an experimental garden in pots where they grew outdoors from 2 February to 23 May (111 days) when treatments were applied. After winter, both grasses were cut to 15 cm in early spring (27 September) and spring growth was measured in November. Shoot biomass was harvested at ground level and separated into lower and upper layers (above and below 15 cm), leaf blades, sheaths and stolons. Daily air temperature, relative humidity and frost events were registered. Allometric analysis of shoot biomass was performed to determine the stress incidence by cold. DF plants achieved 55-80% higher shoot biomass than DFR plants during spring in both species. The allometric analysis revealed for P. coloratum significant relationships between shoot biomass from plant compartments (lower and upper layers, leaf blade and sheath) and total shoot biomass in both treatments, indicating good cold tolerance. However, for C. gayana, unlike DF plants, DFR plants were strongly stressed, showing a lack of shoot biomass fit. These results suggest that deferring autumn forage growth and retaining as winter cover may improve survival during winter and productivity during spring of these two tropical grasses in temperate pastoral systems. However, the study needs to be repeated under field conditions and under grazing or cutting over a number of years in different situations to verify these preliminary results., En La Plata, Buenos Aires, Argentina, en un experimento en macetas a aire libre (condiciones de luz y temperatura naturales) se evaluó el efecto del forraje diferido como cobertura invernal en 2 gramíneas tropicales C4 (Chloris gayana y Panicum coloratum). Plantas adultas fueron extraídas de un establecimiento ganadero, trasplantadas a macetas en un jardín experimental y, después de crecer durante 111 días, sometidas el 23 de Mayo a los tratamientos: (1) control [sin remoción del forraje diferido de otoño (DF)]; y (2) remoción del forraje diferido de otoño (DFR) después de un corte a 15 cm del suelo. Se utilizaron 10 repeticiones por tratamiento y una planta por maceta (unidad experimental). Las plantas fueron cosechadas el 27 de Septiembre (después del invierno) y nuevamente en Noviembre, mediante corte a ras del suelo, para medir la biomasa del rebrote primaveral en los estratos superior (>15 cm) e inferior (, Instituto de Fisiología Vegetal

The study of the anthelmintic properties of plants rich in plant secondary metabolites can provide ecologically sound methods for the treatment of parasites on grazing animals. The purpose of the present study was to evaluate the anthelmintic effect of five tropical native Australian plant species rich in plant secondary metabolites on adult Haemonchus contortus and Trichostrongylus colubriformis in experimentally infected goats. Thirty young, nematode-free goats were infected with 2500 H. contortus and 5000 T. colubriformis infective larvae thrice weekly for a week (day 1-7 of the experiment). On day 27 after first infection, the goats were allocated into six groups of five animals per group. From day 28 to day 35, fresh leaves from Acacia salicina, Acacia nilotica, Eucalyptus corymbia, Casuarina cunninghamiana and Eucalyptus drepanophylla were included in the goats diet. Five groups were offered leaves from one of these plant species and one group, the untreated control, received only the basal diet formulated with 20% Medicago sativa and 80% Avena sativa. Following plant material administration, the goats were monitored daily until day 40 and then slaughtered on day 41. Total faecal worm egg output, total production of larvae recovered from faecal cultures, total post-mortem worm burdens and the per capita fecundity of female worms were estimated. The toxicity of the plant species for the goats was measured by histopathological analyses of liver and kidney samples. Results showed that goats feeding on the plant material rich in plant secondary metabolites had significantly lower egg output compared to the control goats (P0.05). A similar response was found for larval production in both H. contortus and T. colubriformis supporting that egg output was affected in both species. Although the total worm burdens were not affected by the plant material (P0.05), the per capita fecundity was significantly reduced by E. corymbia, A. nilotica and A. salicina (P0.05). No signs of toxicity were detected in the liver or kidney samples. It is concluded that goats can benefit from the short-term ingestion of plant secondary metabolites, which reduce the total faecal egg output and thus decrease the potential for re-infection from the pasture.

The intake of forage grasses by grazing ruminants is closely related to the mechanical fracture properties of grasses. The relationship between the tensile fracture properties of grasses and foraging behaviour is of particular importance in tropical reproductive swards composed of both stems and leaves. This study (i) quantified and compared the tensile fracture properties of stems and leaves of seven tropical grass species and (ii) provided insight into the underlying plant traits that explain differences in fracture properties between species. Fracture force, tensile strength, fracture energy and toughness of stems (in various phenological stages) and leaves were measured and compared among five introduced tropical grasses (Cenchrus ciliaris, Chloris gayana, Digitaria milanjiana, Megathyrsus maximus (syn. Panicum maximum), Setaria sphacelata) and two native tropical grasses (Setaria surgens and Dichanthium sericeum). Species differed significantly in fracture force and fracture energy, with stems and leaves of C. ciliaris and S. surgens requiring less force and energy to fracture and stems and leaves of M. maximus and S. sphacelata requiring more force and energy to fracture in comparison with the other species. Differences in tensile strength and toughness were less pronounced. The differences among species in fracture force and energy mainly resulted from differences in cross-sectional area of plant parts rather than from differences in tensile strength and toughness.

The rate of nutrient intake (RNI) is a primary determinant of animal performance in grazing cattle and depends on both diet quality and instantaneous intake rate (IIR). In turn, diet quality and IIR are a function of the foraging behaviour of the animal (selectivity, bite mass and bite rate) and the characteristics of the sward. In this study we evaluated the effect of the stem density and the tensile resistance of stems on the foraging behaviour of cattle grazing tropical pasture species. The methodology involved the use of small sown microswards offered to tethered cattle. The experiment consisted of a factorial combination of five tropical grasses [ Bothriochloa pertusa (Bp), Chloris barbata (Cb), Chloris gayana (Cg), Cynodon dactylon (Cd) and Heteropogon contortus (Hc)] and three stem densities (0, 400 and 800 stems m − 2 ). Bp and Cd had stems of significantly lower tensile resistance (19 and 15 N respectively) (Group 1) than those of Cb, Cg and Hc (110, 211 and 167 N respectively) (Group 2). The steers avoided stems of Group 2 and thus, reduced bite area, bite mass, IIR and RNI as stem density increased. However, the animals did not avoid stems of Group 1 and there was no effect of stem density on any of the foraging behaviour variables when cattle grazed species in Group 1. These results confirm that RNI and plant part selection is closely associated with the tensile resistance of the stem.

The effects of stem density of tropical swards and age of cattle on their foraging behaviour were evaluated using artificial microswards, consisting of leaves of 20 cm in height and high tensile-resisting stems of 25 cm in height of Panicum maximum. The treatments consisted of a factorial combination of four stem densities of swards (0, 100, 200 and 400 stems m(-2)) and two ages of cattle (1- and 3-year-old steers). There was a significant interaction between stem density of sward and age of cattle for bite area (BA), bite mass (BM) and instantaneous intake rate (IIR). Stem density had a significant negative effect on these variables describing ingestive behaviour which was particularly strong for older steers. In leaf-only swards, mature cattle achieved a much greater BA (106.5 vs. 57.9 cm(2)), BM (0.88 vs. 0.47 g DM) and IIR (46.9 vs. 17.2 g DM min(-1)) than did young cattle. However, these variables were very similar across ages of cattle at the highest stem density of sward. These results show the importance of the high tensile-resisting stems as deterrents of the grazing process in tropical pastures, particularly in older cattle.

in reproductive swards, stems appear to act as vertical or horizontal barriers to bite formation, influencing instantaneous intake rate (IIR). The hypothesis was tested that the stems' barrier effect is determined by the physical properties and density of stems. Artificial microswards, consisting of 20-cm leaves and 15-cm stems of Panicum maximum, were offered to three steers (362 kg) in a factorial combination of three stem densities (0, 100 and 400 stems m(-2)) and two levels of stem tensile resistance [low (LTRS) and high tensile-resisting stems (HTRS)]. LTRS were not a barrier to defoliation and did not affect bite depth and bite mass. HTRS acted as both a horizontal barrier and a vertical barrier depressing bite depth (13.4, 13.6 and 5.1 cut for 0, 100 and 400 stems m(-2), respectively), bite area (89.3, 50.8 and 47.6 cm(2) for 0, 100 and 400 stems M-2, respectively), bite mass (0.51, 0.29 and 0.11 g for 0, 100 and 400 stems m(-2), respectively) and IIR (23.8, 10.5 and 3.6 g sec(-2) for 0, 100 and 400 Stems m(-2), respectively). The results confirmed the importance of the density and physical properties of stems as determinants of the stems' barrier effect on bite dimensions and IIR.

A new rotational-grazing management strategy called PUP-grazing (proportion of un-grazed pasture, which is the estimated percentage of pasture vegetation without signs of being consumed) was compared with the traditional rotational-grazing management strategy (TGMS, which is based on residual sward height) using Brahman cross steers on Axonopus catarinensis over two periods (2013/14 and 2015/16) in Misiones, Argentina. The proportion of un-grazed pasture for PUP and TGMS was 11.5 and 3.4%, respectively, of the pasture area. Average daily liveweight gain/animal was significantly higher for PUP than for TGMS (606 vs. 420 g/d; P

Phosphorus (P) deficiency is a major constraint to the productivity of breeder herds grazing low-P rangelands due to adverse effects on growth and fertility. However, P supplementation during the wet season, when additional dietary P is most needed, is often difficult due to practical constraints. Body P reserves in breeders can be mobilised and alleviate dietary P deficiency within an annual cycle. Approaches to estimate bone P reserves and net mobilisation or replenishment of P from the analysis of rib and hip (tuber coxae) biopsies are discussed. In at least some circumstances, breeder cows grazing P-deficient pastures mobilise bone P to alleviate the effects of diet P deficiency. Recent experiments with breeders have investigated mobilisation of body P to alleviate the adverse effects of dietary P deficiency during pregnancy and early lactation, and subsequent replenishment of body P reserves. Both mature cows and first-calf cows (FCC) calving in a high P status and fed severely P-deficient diets during lactation were able to mobilise sufficient body P reserves to provide milk for moderate calf growth (viz. 0.6–0.8 kg liveweight (LW)/day for 3 months), but this was associated with rapid cow-LW loss and markedly decreased bone P content. First-calf cows appear to have lesser capacity than mature cows to mobilise body P. FCC fed P-adequate diets during late pregnancy maintained high voluntary intakes and had higher LW and bone P reserves at calving. When fed a P-deficient diet during early lactation, these greater bone P reserves were utilised. Bone P reserves can be replenished by P-adequate diets fed post-weaning. Breeder management that relies more on mobilising body P reserves when P demands are high and on replacing these body P reserves when P demands are lower offers an opportunity to alleviate the effects of dietary P deficiencies during the early wet season in situations where P supplementation is not possible.

Determining the phosphorus (P) status of cattle grazing P-deficient rangelands in northern Australia is important for improving animal production in these areas. Plasma inorganic P concentration is currently the best diagnostic marker of dietary P deficiency in growing cattle but is not suitable for assessing the P status of breeder cows, which often mobilise substantial bone and soft tissue reserves in late pregnancy and lactation. Markers of bone turnover offer potential as markers of P status in cattle, as they reflect bone mobilisation or bone formation. Recent experiments investigating the physiology of beef breeder cows during diet P deficiency have indicated that the ratio of plasma total calcium concentration to plasma inorganic P concentration might be suitable as a simple index of P deficiency. However, a more specific measure of increased bone mobilisation in P-deficient breeders is plasma concentration of C-terminal telopeptide of Type 1 collagen. Also, plasma concentration of bone alkaline phosphatase is a marker of defective bone mineralisation in dietary P deficiency. These candidate markers warrant further investigation to determine their predictive value for P deficiency in cattle.

With the purpose of studying the anthelmintic efficacy of some plant species presents in Queensland State, Australia, we tested in vitro the effect of plant extracts on infective larvae (L3) migration of Haemonchus placei, Cooperia sp., Haemonchus contortus and Trichostrongylus colubriformis. In general, plant extracts reduced the larval migration of Haemonchus placei and Cooperia sp. The most effective plants against Haemonchus placei and Cooperia sp. (P < 0.0001) were Allocasuarina torulosa, Neolitsea dealbata, Acacia holosericea, Acacia salicina, Callitris endlicheri and Casuarina cunninghamiana. Plants extracts were less effective on L3 migration of Haemonchus contortus and Trichostrongylus colubriformis. Callitris endlicheri, Casuarina cunninghamiana, Acacia farnesiana, Acacia holosericea and Acacia nilotica were the plant extracts that shown an important larval migration inhibition against H. contortus and Trichostrongylus colubriformis (P < 0.0001). Callitris endlicheri was the plant that consistently inhibited the larval migration of every nematode species under study. These in vitro results suggest anthelmintic properties associate with some of the plant species we studied. EEA Cerro Azul Fil: Moreno, Fabiana Carina. University Drive. CSIRO Davies Laboratory; Australia. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad Ciencias Veterinarias; Argentina. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Montecarlo; Argentina Fil: Gordon, Iain J. University Drive. CSIRO Davies Laboratory; Australia Fil: Wright, A.D. AIMS Australian Institute of Marine Science; Australia Fil: Benvenutti, Marcelo. University Drive. CSIRO Davies Laboratory; Australia. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Montecarlo; Argentina Fil: Saumell, Carlos A. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad Ciencias Veterinarias; Argentina

For grazing animals an important determinant of animal performance is the rate of nutrient intake (RNI) which depends on diet quality and instantaneous intake rate (IIR). In turn, diet quality and IIR are the outcome of the interaction between the morphology and behaviour of the animal and the structure of the sward. Using artificial microswards of Panicum maximum we evaluated the effect of four levels of the tensile resistance of stems in tropical swards on the grazing behaviour of cattle of two age classes (1- and 3-year-old steers) faced with a stem barrier either in a vertical (experiment 1, El) or horizontal plane (experiment 2, E2). The animals did not select against low tensile resistance stems (LTRS) but did avoid high tensile resistance stems (HTRS) which resulted in a significant difference (P < 0.001) between diet DM (dry matter) digestibility and forage DM digestibility in swards with HTRS. IIR decreased (P < 0.001) on average 62% in El and 67% in E2 as stem tensile resistance increased, 144% and 177% in El and E2, respectively. This led to a reduction (P < 0.001) in digestible DM IIR in both young and mature cattle respectively of 56% and 68% in El, and 45% and 79% in E2, as stein tensile resistance increased. The decline in IIR was due to an increase in time per bite and a reduction in bite dimensions that were the result of different mechanisms in the two experiments: when leaves were taller than the stems (E1) the decrease in bite area was associated with an asymptotic increase (P < 0.001) in bite force in mature animals, and a maintenance (P = 0.456) of bite force in young animals, suggesting that maximum bite force regulated bite area in El. This was not the case in E2 because both bite area and bite force decreased (P < 0.05) with the increase in stem tensile resistance suggesting that the animals were not able to gather enough plant material with the tongue in order for bite force to regulate bite area. We conclude that bite force and tongue force regulate selectivity and bite dimensions, which are the ultimate determinants of the RNI; HR is the primary determinant of the RNI with diet quality being of lesser importance; and HTRS act as deterrents to achieving maximum HR in tropical swards, particularly in mature cattle. Refereed/Peer-reviewed

A technique combining open-path Fourier transform infrared spectroscopy with an inverse-dispersion model was used to quantify methane (CH4), nitrous oxide (N2O) and ammonia (NH3) emissions from an isolated cattle pen in south-eastern Australia. Twenty-eight Angus steers (1-year old, initial average liveweight 404 kg) were fed a 60% grain diet and kept in a pen (20 × 20 m) for 41 days. Gas concentrations were measured downwind of the pen using an open-path Fourier transform infrared spectroscopy with a path length of 100 m, having a detection sensitivity of 2, 0.3 and 0.4 ppb for CH4, N2O and NH3, respectively. Daily emission rates were 232, 14 and 192 g/cattle.day for CH4, N2O and NH3, respectively. The measured CH4 emissions were in agreement with predictions based on Australian National Inventory recommendations, however, measured N2O and NH3 emissions were much higher than the predicted values. Extrapolation of our measurements would mean that CH4 and N2O emissions from beef feedlot cattle contribute 3.1% and 5.9% of the Australian agricultural CH4 and N2O emissions, respectively.

A fast response open-path methane analyzer was deployed at a research farm in north Queensland for one year as part of an eddy covariance flux system to calculate methane fluxes on a cattle grazed landscape.