Three grasses and two legumes, each at two stages of maturity, were fed to three fistulated sheep and samples of the feed, and faeces and contents of the reticulorumen, abomasum and ileum were collected for the determination of particle size by wet sieving. Modulus of fineness (MF) was calculated for all particulate matter that failed to pass a 0-15 mm screen. Resistance to flow from the rumen of feed particles of different sizes was also calculated.The mean MF of the reticulo-rumen contents was 2-56 compared with 5-72 for the feed. Material leaving the rumen and found in the abomasum had a MF of l -67 and subsequent changes were small and not significant; ileum 1-63, faeces 1-80. Particles greater than 1-18 mm passed out of the reticulo-rumen although the quantity was small (1-3 %). The resistance to flow of particles of different sizes from the reticulorumen was closely related to particle size with no difference between grasses and legumes or between young and mature forages.It was concluded that in modelling the flow of particles from the reticulo-rumen a non-compartmentalized approach should be adopted, but if a simple two-compartment model is required then a critical sieve size of about 1-18 mm may be useful, since less than 5 % of the particulate material is retained on this sieve size.

I.A study of ammonia and urea metabolism in sheep was made using isotope dilution techniques with (lSNH4),S04, [lSN]urea and [Wlurea in order to determine quantitatively the movements of urea-N and NH,-N throughout the body of normal, feeding sheep.2. Single injections of 15N-labelled compounds were made into the rumen fluid NH,, caecal fluid NH, and the blood urea pools, in order to estimate the rates of flux through, and the transfer of N between, these and other nitrogenous pools in the body. fWr EDTA was injected into the rumen and caecum with (16NH&S0, to allow estimation of fluid volumes and to provide an indication of mixing, and of times of transit of isotopes between different sampling sites in the digestive tract.3. The sheep ate approximately 22 g lucerne chaffjh and the mean dietary N intake was 16.3 g/d.4. The rate of flux of NH, through the rumen NH, pool was 15.0 g/d (i.e. 90y0 of the dietary N ingested; however, this amount also included N from plasma urea (1.1 g/d) and other endogenous sources including NH, derived from caecal NH, (0.4 g/d).5. Only 40% of the N in isolated rumen bacteria was derived from NH,, indicating that a considerable proportion of their N requirements were obtained from compounds other than NH, (e.g. peptides and amino acids).6. There was evidence of recycling of N between nitrogenous pools in the rumen, probably through rumen NH, -+ microbial N --+ NH,. 7.It was estimated that 5-3 g blood urea-N/d entered the digestive tract: 20% of this urea was degraded in the rumen, 25 yo in the caecum and the remainder was apparently degraded elsewhere; there was evidence of urea degradation in the large intestine posterior to the caecum and it is suggested that urea degradation and absorption of the resultant NH, may occur in the ileum. 9.A large proportion of the NH, entering the caecal NH, pool (70% or 3.2 g N/d) was apparently derived from degradation of nitrogenous products, other than urea, including rumen microbial N (1.0 g N/d) passing undigested from the small intestine. 10. Less than half the NH,-N of caecal origin entering the rumen passed through the blood urea pool; the remainder was apparently transported as other nitrogenous compounds in the blood or body fluids.11. The results of the three experiments were combined in a general three-pool, opencompartment model which formally recognizes an unlimited number of other unspecified, interconnected pools together comprising the whole-animal system. Rates of flux through, and transfer of N between these and other nitrogenous pools in the body were calculated by solving this model and the information derived has been applied to whole-animal models with a view to subsequently using these models in computer simulation studies.

A factorial experiment was conducted to study the effects of condensed tannins (CT) from the tropical legumes Desmodium intorturn and Calliandra calothyrsus on the digestion and utilization of protein and carbohydrate in sheep and goats. CT-free Centrusema pubescens was also fed for comparison with the CT legumes, and each legume was included (300 g/kg DM) in a basal diet of pangola grass (Digitmia decumbens). Pangola grass alone was used as a control diet. There were no significant (P > 0.05) differences between sheep and goats for the efficiency of digestion of N (0.574, SE 0013), organic matter (OM; 0.519, SE 0.010), neutral-detergent fibre (NDF; 0524, SE 0.011) and acid-detergent fibre (ADF; 0.407, SE 0.016). Diets containing desmodium and calliandra were digested less well in the rumen (64 and 62 % of total OM digested) when compared with the pangola and centrosema diets (74 and 73% of total OM digested in rumen). There was an apparent net gain of 30% in ADF across the digestive tract of sheep and goats given calliandra, and this gain was ascribed to the formation of 'artifact' fibre as a result of fibre-tannin interaction. Overall, inclusion of legume at 300 g/kg in the diet significantly increased (P < 0.05) the concentration of acetic acid and decreased butyric acid concentration in the rumen fluid of sheep and goats. Significantly higher proportions of dietary N apparently reached the abomasum of animals given the diets containing desmodium (50 YO) and calliandra (56 %) when compared with animals given the centrosema and pangola diets (35%). Sheep and goats given the CT diets also had higher excretions of faecal N. Ihis increment of faecal N (14%) did not affect post-rumen N digestion (P > 0-05) since animals given CT diets absorbed more N (19%) per kg total OM digested than those given the control diets. It was concluded that whilst the low levels of CT provided in desmodium (1.0%) and calliandra (2.3 YO) diets protected dietary protein from degradation in the rumen, there were no overall beneficial or detrimental effects of CT in these diets for sheep or goats. A method was developed to categorize CT into fractions representative of their forms (free, protein-bound, and fibre-bound) during the digestion process. A quantitative model of CT metabolism during passage through the digestive tract was developed from the measured exchanges of CT between free, protein-bound and fibre-bound pools in the rumen and lower digestive tract. CT interchange mainly occurred in the reticulo-rumen of both animal species. Desmodium and calliandra free CT showed net losses of 68 and 78% in the rumen respectively and 57 and 68% of the fibre-bound CT was lost in the same site for sheep and goats respectively. However, protein-bound CT increased across the rumen by 73 and 56% for both animal species. Post-rumen losses of the total CT abomasal flow were 86 and 83 % (free CT) for sheep and goats respectively, 70 and 66 YO (protein-bound CT), whilst 28 % loss of fibre-bound CT occurred in sheep and goats respectively.

The effects of season and diet on LH, FSH and testosterone concentrations, testicular mass, sebaceous gland volume and male odour were examined in mature Australian cashmere goat bucks fed ad libitum with diets of low or high quality for 16 months under natural photoperiod at 29 degrees S, 153 degrees E (n = 6 per treatment). Each week plasma was sampled, the bucks were weighed, scored for male odour and assessed for testicular mass based on scrotal circumference. Each month a skin sample was taken from the occipital region for histological assessment of sebaceous gland volume. For each variable there was a clear circannual cycle that was significantly influenced by dietary treatment. In bucks fed the low-quality diet, the timing of seasonal changes in LH and testosterone concentration, sebaceous gland volume and odour score was similar, with a mid-autumn peak. In each case the high-quality diet advanced, extended the duration and increased the magnitude of the seasonal increase. FSH concentrations peaked in late spring (in bucks on the high-quality diet) or summer (in bucks on the low-quality diet), reaching a nadir in early winter. The high-quality diet significantly increased concentrations only in the last 2 months of the experiment (spring). There was no overall association between these variables and change in testicular mass; instead, it was strongly correlated with voluntary feed intake and change in body mass, themselves subject to seasonal variation with a winter or spring peak. The high-quality diet induced large increases in body mass and testicular mass during the first months of the experiment without influencing the seasonally low concentrations of FSH, LH and testosterone present at the time. These results demonstrate that the male, like the female, Australian cashmere goat, exhibits marked reproductive seasonality, and that nutrition is a powerful modulator of the seasonal cycle. They suggest that testosterone concentration, sebaceous gland volume and odour score are ultimately dependent upon LH secretion, which appears to be under strong seasonal (photoperiodic) control, with the effects of enhanced nutrition limited to periods when photoperiodic inhibition is waning. However, seasonal regulation of testicular mass, and therefore sperm production, appears to be primarily dependent on changes in voluntary feed intake and growth, with the seasonal cycle of testicular mass more a consequence of the seasonal appetite or growth cycle than of changing gonadotrophin concentrations.

In a double-blind study, the influence of biotin supplementation on lameness in dairy cows was investigated over a 13-mo period. The experimental site was a tropical upland environment and involved over 2705 Holstein and Friesian cows on 20 participating farms. Cows on 10 farms received biotin at a rate of 20 mg/head per day in the concentrate, and cows on 10 other farms received feed without the biotin supplement. Premixes with or without biotin were incorporated into a grain concentrate that was fed at a constant rate to cows at milking. Farmers maintained accurate records of the nature of hoof problems and any treatment applied. Each herd was evaluated for locomotion scores at 8-wk intervals. Locomotion scores were significantly correlated with the number of days with measurable rainfall per month (r = 0.88). The biotin-supplemented herds exhibited better locomotion scores than the unsupplemented herds. In the wet summer period the number of lame cows, as observed by the farmer, were significantly fewer during the rainy period for the biotin-supplemented herds and required fewer antibiotic treatments than unsupplemented herds. Most hoof lesions were most commonly observed in the outer claws of the hind limb. Daily milk production (17.3 vs. 18.5 L) was not affected by biotin supplementation. Reduced milk fat percentage and somatic cell counts of bulk milk were recorded in the biotin supplemented herds during the wet, summer period.

In interaction of condensed tannins from Desmodium intortum and Lotus pedunculatus and tannic acid (hydrolysable tannin) with salivary mucoproteins (from sheep and goats), plant leaf proteins and bovine serum albumin were evaluated. These studies were carried out over a p H range of 2.0-9.0 and different inorganic ion conditions to simulate conditions in which dietary proteins would interact with tannins in a ruminant digestive tract. Insoluble tanninprotein interactions were found at pH 4.5-5.5 for bovine serum albumin and 3.5-5.5 for plant leaf protein. The present study showed that pH alone was not the sole determinant for tannin-protein complex formation, since tannin-protein complexation was found in the pH range 6.0-6.5 when different inorganic ions were added to the solutions. Insoluble complexes were not formed with salivary proteins, although precipitation by tannic acid was achieved at 5°C. This suggests that tannins may form soluble rather than insoluble complexes with salivary proteins. It was concluded that purified F1 leaf protein (the major protei occurring in leaf tissue) ought to be used as the test protein for evaluating tannin-protein interactions for in uitro assay procedures. Using this method it was calculated that 27-43% and 19-40Y0 of available plant protein may interact with condensed tannins from Desmodium intorturn and Lotus pedunculatus, respectively.

An experiment was conducted to investigate the metabolism of condensed tannin (CT) in sheep and goats offered a mixture of Digitaria decumbens (700 g/kg) and Desmodium intortum (300 g/kg) hay. Radioactive 14C0, was used to label CT in young growing desmodium plants, [14C]CT was extracted, purified and infused intraruminally, and the metabolism of [14C]CT was followed in the rumen and lower digestive tract of both species. Digestion of DM, organic matter (OM), cell-wall constituents (CWC), N and the efficiency of rumen microbial synthesis were determined using a continuous intraruminal infusion of 51Cr EDTA, YbCl, and Na,3%04. The measurements taken for sheep and goats respectively were: intake, 21 and 30 g/kg0'' per d; digestibilities (g/g) of DM, 0.566 and 0.505; OM 0.578 and 0.508; neutral-detergent fibre, 0.584 and 0.532; and acid-detergent fibre, 0.535 and 0435. None of these measurements was significantly different (P > 0.05) between animal species. There was an apparent net gain in lignin across the rumen and whole intestinal tract for both animal species (19 and 29 YO for sheep and goats respectively). There were no significant differences between sheep and goats (P > 0.05) detected for any measurements of N excretion and utilization. The overall efficiency of N digestion and utilization was also similar between species. The routes of CT metabolism were compared for both colorimetric estimates (butanol-HC1) of dietary C T (DCT) and the specific radioactivity of [14C]CT in digesta (abomasum) and excreta (urine and faeces) of both sheep and goats. [14C]CT showed total losses of 57 and 56 % in sheep and goats respectively whilst losses of DCT of 71 and 70 % were detected with butanol-HC1 in sheep and goats respectively. The apparent losses of DCT across the rumen of sheep and goats were 12 and 9 % whilst higher losses (49 and 42 % for sheep and goats respectively) were observed for [14C]CT. Losses of DCT in the lower intestinal tract accounted for 69 and 71 % of the total C T leaving the abomasum. By comparison, only 40 and 35 % of [14C]CT was lost during intestinal passage in sheep and goats respectively. It was concluded that the infused free [14C]CT interacted with DCT and entered the protein and fibre-bound DCT pools. The loss of DCT during passage through the intestines was considered to be a consequence of either absorption of free CT or the degradation products of CT.It was assumed that free C T arose in the lower gastrointestinal tract from protein-CT and fibre-CT dissociation to be digested and/or absorbed. The higher recoveries of [14C]CT in faeces (32 and 35 %) compared with DCT (27 and 26 %) for sheep and goats respectively) were associated with the excretion of [14C] degradation products or conjugates which were not reactive to butanol-HC1. It was concluded that both methods (butanol-HC1 and labelling C T with 14C) detected a substantial disappearance of CT (free, protein, and fibre-bound) during metabolism in the gastrointestinal tract in sheep and goats.

SummaryElimination of the rumen anaerobic fungi from sheep fed chemically-treated barley straw diets resulted in elevated proportions of propionic acid in rumen liquor (fromca. 0·15 to 0·30). Subsequent inoculation of these sheep with a pure culture of fungus decreased propionate concentrations within 3 days to the levels observed in control animals that possessed abundant fungal populations throughout the experiment.Confirmation that propionate itself was not responsible for the elimination of the fungi was provided by the results of a second experiment in which intraruminal infusions of propionic acid failed to reduce fungal growth or prevent recolonization in sheep previously rendered fungi-free.In a third experiment with sheep fed untreated barley straw, monensin supplementation produced the well known elevation of propionate concentrations. However, this treatment also resulted in the elimination of rumen anaerobic fungi from the animals. The magnitude of the increased concentration of rumen propionic acid, resulting from the elimination of the anaerobic fungal flora, indicates an important role for the fungi in the fermentation of high-fibre diets. In addition, these findings indicate that the well known elevation of propionate levels produced by monensin may likewise be effected directly by removal of the rumen anaerobic fungi.