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The aim of this study was to determine the optimal amino acid balance in dietary protein for the growing pig. The method used was based on the principle that removal of any amino acid in excess of that required in this amino acid pattern should not affect nitorgen retention. A semi-purified diet based on casein and amino acids was used in a series of experiments. A proportion of each amino acid was removed in turn from the control amino acid pattern to determine how much could be removed without affecting nitrogen retention. The effect of changing the ratio of essential: non-essential amino acid was also examined. From these experiments an ideal dietary amino acid pattern for growing pigs was determined. This pattern was utilized significantly better than that proposed by ARC(1981). The property that in such an ideal pattern each amino acid should be equally limiting was tested and confirmed in both short and long term nitrogen balance trials. In the final experiment, the optimum ratios between lysine, methionine, threonine and tryptophan at two different rates of growth were determined using diets based on maize and soya bean meal. It was found that less threonine was needed than was deduced from the experiment with semi-synthetic diets. From the results of all the experiments the following amino acid pattern (g/160gN) is suggested: lysine 65, methionine + cystine 39, threonine 43, tryptophan 12, valine 49, isoleucine 39, leucine 72, phenylalanine + tyrosine 78, histidine 25.

The relationship between dietary nutrient inputs, particularly energy and protein, and their partition between fibre, meat and other non-meat components in British fibre producing goats was studied in a series of four experiments. Experiment 1 indicated that increasing dietary energy concentration from 10.2 to 11.9 MJ ME/kg dry matter (DM) significantly (P &'60 0.05 to 0.001) improved liveweight gain, feed conversion efficiency, carcass weight, cross sectional area of M.longissimus dorsi , and increased fat thickness over N.serratus dorsalis . Values were also increased in the carcass for dissected lean tissue and crude protein, weights and proportions of dissected and chemically extractable fat, weights of liver, kidneys and also fat deposition in the omental and perirenal plus retro-peritoneal depots. No consistent effects due to dietary energy inputs were observed for yield and diameter of mohair fibres. Similarly, changing the dietary protein concentration from 108 to 180 g/kg DM resulted in significantly (P &'60 0.05 to P &'60 0.001) increased values for live weight gain, DM intake, feed conversion efficiency, carcass weight, killing out proportions, area, width and depth of M.longissimus dorsi , weights of dissected carcass lean tissue, chemically determined crude protein and lipid in the carcass and also greater yield and diameter of mohair fibres. The results of experiment 2 indicated that increasing dietary protein concentrations (102, 126, 165, 185 g/kg DM) by the inclusion of fish and soya bean meal increased (linear effect, P &'60 0.05 to P &'60 0.001) live weight gain, feed conversion efficiency, carcass weight, width of M.longissimus dorsi , weight and proportion of dissectible carcass lean tissue and weight of crude protein in the carcass, liver and kidneys. The clean fibre yield and diameter were increased as the dietary CP concentration increased from 102 to 165 g/kg DM and then decreased at the highest CP concentration of 185 g/kg DM. Experiment 3 showed that source of nitrogen supplementation (urea, fish meal or soya bean meal) had no significant effects on growth rate, DM intake, feed conversion efficiency and nitrogen balance. However, soya bean meal supplementation resulted in significantly (P &'60 0.05 to P &'60 0.001) higher values for nitrogen digestibility, carcass weight, killing out proportion, dissectible lean tissue with trends to increase area of M.longissimus dorsi and microbial protein synthesis. The yield and diameter of mohair fibre were increased (P &'60 0.05) due to protein supplementation compared with the NPN supplementation in the diet. Experiment 4 indicated that average growth rate, DM intake, feed conversion efficiency, carcass weight and killing out proportions were not significantly different for the source of nitrogen supplementation (urea v fish meal) or for the genotype of Cashmere goats (Russian v Australasian crosses). Mid-side fleece growth (Cashmere &'43 guard hair) was significantly (P &'60 0.05) higher in goats given fish meal rather than urea supplemented diet and Russian goats tended to produce higher proportion of cashmere in the mid-side and in total fleece samples than those of Australasian genotype.

The welfare of young pigs was compared in different housing systems using a range of indicators. Groups of twenty pigs were weaned at 6.4 kg into each of four pens built within environmentally-controlled rooms: a) deep-straw; b) Straw-Flow(R) (1 kg straw daily); c) large expanded metal-floored flatdeck; d) small flatdeck. Kennelled lying areas were provided in a and b. Stocking densities were 0.229 m2/pig for a,b and c, and 0.173 m2/pig for d. After 4-5 weeks (19.6 kg liveweight), sixteen pigs from each pen were moved into Straw-Flow grower pens (0.675 m2/pig) and observed until slaughter at 90.6 kg. The remaining pigs were grouped together to examine the effects of mixing. Housing type did not affect growth and feed intake. Food conversion ratio was poorer in large flatdeck than in small flatdeck or Straw-Flow. Behavioural differences between Straw-Flow and deep-straw related to differences in available straw; there were few differences between flatdecks. Access to straw affected pig-directed, pen-directed and straw-directed behaviours. Foot injuries recovered rapidly on deep-straw and increased in flatdecks immediately after weaning (Straw-Flow intermediate); injuries were more persistent in small flatdeck. Deep-straw prevented adventitious bursitis of the hock. Antibody response was examined by challenge with keyhole limpet haemocyanin (KLH). Immunoglobulin (Ig) M response was greater in straw pens. Dust concentration was higher in kennelled lying areas than flatdecks. With removal of kennels, straw pens showed less dust than flatdecks. Thus, welfare of early-weaned pigs in deep-straw was very good, flatdecks poor with Straw-Flow closer to deep-straw than to flatdecks. Early experience had limited effects. Pigs from flatdecks performed increased rooting relative to deep-straw two weeks after moving (Straw-Flow intermediate). These differences did not persist. Pigs mixed at 20 kg showed increased aggression (not significant) and decreased Ig m response to KLH, indicating reduced welfare.

Three studies were conducted on commercial farms. Study 1 sought to compare four combinations of natural mating (NM) and AI, namely AI + AI, AI + NM, NM + AI and NM + NM (first mating on day 1 of oestrous and second on day 2), and evaluate what aspects of insemination quality are related to fertility. The respective farrowing rates (FR) of AI + AI, AI + NS, NS + AI and NS + NS were (number of sows in parentheses) 92.9% (141), 89.6% (134), 89.3% (140) and 89.0% (100) and litter size (LS) was 11.31, 10.49, 11.50 and 10.61 (total births). The number of pigs born per 100 sows mated were 1051, 940, 1027 and 944. Both FR (P < 0.05) and LS (P < 0.01) were significantly influenced by parity. Sow behaviour during insemination significantly influenced (P < 0.01) FR and LS, the mean FR of calm and agitated sows being 91.3 and 83.1 percent and the mean LS being 11.32 and 10.22 respectively. Loss of semen due to backflow during insemination significantly reduced (P < 0.05) FR in sows having one AI. Backflow losses were significantly lower (P < 0.01) in calm than in agitated sows. It was concluded that AI, either alone or in combination with NM, yields fertility results comparable to NM alone and that sow behaviour during insemination has an important effect on sow fertility. Study 2 tested the effect of the addition of 5 i.u. of oxytocin to semen immediately before AI on fertility at two farms. Overall oxytoxin significantly improved FR (P < 0.05) from 73.2 percent (429) to 79.5 percent (385) and substantially improved litter size from 10.70 to 11.18. There was a significant (P < 0.05) treatment x farm interaction, FR on farm A improving from 77.2% (control) to 78.0% (oxytocin) whereas FR on farm B improved from 69.7% (control) to 84.0% (oxytocin). It was hypothesised that differences between farms in operator skill during insemination may have mediated the differing response to oxytocin.

The protein requirements and nutrition of bulls intensively reared on barley were investigated in the light of current knowledge of protein metabolism in the ruminant. Five experiments were carried out using cattle and sheep. 1. The response of barley beef bulls to RDP and UDP supplementation was examined. Although results were not significantly different, urea supplemented diets gave the highest growth rates of 1.45 and 1.47 kg/d; soya bean meal supplemented diets gave growth rates of 1.31 and 1.36 kg/d while the unsupplemented barley diet gave a growth rate of 1.23 kg/d. Feed conversion ratios ranged from 5.89 to 6.51. 2. The response of barley beef bulls to barleys of different protein content and degradability and to RDP and UDP supplementation was examined. Results were not significantly different although the high protein, low dg barley gave slightly lower liveweight gains (1.29 and 1.24 kg/d) than the low protein, high dg barley (1.32, 1.33 and 1.34 kg/d). RDP and UDP supplementation gave no additional growth response on any of the diets. Feed conversion ratios were approximately the same as the first trial ranging from 6.08 to 6.65. 3. A study of the barley-beef diets used in the first bull trial was carried out using surgically modified sheep fitted with Ash-type re-entrant cannulae in the duodenum. Five of the six animals died shortly after surgery and it was concluded that the surgery, and the type of cannulae used were a major factor causing this. 4. A study of the barley-beef diets used in the second bull trial was carried out using surgically modified sheep fitted with Hecker-type re-entrant cannulae. 24 h duodenal digesta collections with Cr2O3 as a marker were carried out followed by 7 d nitrogen balance and digestibility trials. Results obtained were nullified by incomplete marker recovery and it was concluded that the Hecker-type of re-entrant cannulae may be unsuitable for total digesta collection. The low protein, high dg barley diets were more digestible than the other barley diets and it was suggested that this may have improved rate of microbial synthesis in the bulls fed on these diets. 5. A study was carried out to examine certain factors affecting the degradability of barley as determined by the nylon bag technique. Variety, CP content and nitrogen fertiliser treatment were studied. Variety had a significant effect on dg (0.15-0.42), malting varieties being more degradable. Degradability tended to decrease as nitrogen fertiliser level increased (0.06-0.23). There also seemed to be a general trend that as CP content increased, dg decreased (0.6-0.8). The results were discussed in relation to current knowledge of ruminant protein metabolism. The new ARC protein system was shown to be acceptable as a framework and the need for more practical data was emphasised.

The genetic outcome of operating an open nucleus system (ONS) in a population of 1200 sheep divided into individual flocks, was investigatd using simulation techniques, and a comparison to alternative breeding systems was made. Selection was for best linear unbiased prediction of breeding value (EBV) for a trait measurable on individuals before selection. Migration of animals between flocks was based on the EBV. The results of stochastic simulations indicated that, compared to selection within closed flocks (CF), the annual genetic gain could be increased by 25 to 40 per cent if an ONS was operated. The variation in selection response, and the rate of inbreeding were also lower. Simulation results showed that approximately 25 per cent of nucleus sires should be selected from the base flocks. Initial genetic differences between flocks had a short term effect on genetic gain in the ONS. Screening the population to ensure that the nucleus flock was initially composed of the best ewes, also only had a short term effect. The advantage of an ONS over CF selection was effected by flock size but not intitial heritability. The use of dispersed nucleus system and a sire referencing scheme with selection of sires across flocks, was investigated. The outcome of these systems was very similar to the ONS. The higher rate of genetic gain achieved in the ONS, compared to CF selection, was attributed to higher genetic selection differentials and maintenance of genetic variation within flocks. These effects were included in a deterministic model of the ONS. The model described the simulated data well, although changes in genetic variance at the outset of the ONS were underestimated. Failure to account for finite population effects in previous studies has resulted in underestimation of the benefits of an open nucleus system in small populations.

Chapter 1: This chapter is a review of literature covering different aspects of ruminant forage nutrition. In this review, aspects of the rumen and its microbial environment and the nutrition requirements of rumen microbes, plant cell wall structure and its degradation by rumen microbes and the regulation of feed intake and digesta flow in ruminants are covered. The last part deals with supplementation of low quality forage diets, with emphasis on the use of high quality forages as supplements and their effect on food intake. Chapter 2: The first part of this chapter describes the experimental methods and analytical techniques used, and the source and analysis of forages used in this study. Natural pasture (veld) hay harvested in the dry season was used as the poor quality forage. Napier hay, harvested at 4 weeks growth during the wet season, and groundnut hay, harvested when the crop was mature, were used as the supplementary high quality forages. Veld hay had a low nitrogen and high NDF content (3.8 and 848 g/kg DM respectively), while napier hay and groundnut had high nitrogen and low NDF content (22.1, 21.0 and 700, 455 g/kg DM respectively). These differences in nutritive value indicated by chemical composition were confirmed by in sacco dry matter degradation and in vitro gas production tests. Groundnut hay, despite having a high solubility and high rate of degradation, had the least degradable cell walls due to lignification. Chapter 3: Expts 1 and 2. The objective of these experiments was to test the response in intake and digestibility, to supplementation of veld hay with different levels of napier or groundnut hays when the basal diet was not supplemented with urea. With both napier hay and groundnut hay, supplementation increased total feed intake (P < 0.05). There was a tendency for the intake of veld hay to be decreased by high levels of forage supplement.

One of the main deterrents against group-housing systems of dry sows is the aggression between animals and the expensive designs necessary to prevent this. This is related to the low feeding level accepted in practice. The low level of feeding is also linked to the occurrence of stereotypies which are generally accepted as an indication of poor welfare. An ad libitum feeding system which does not result in excessive intake and concomitant problems of obesity, might improve sow welfare and have economical advantages in reducing capital cost. Suitable diets might be high-fibre diets. High inclusion levels of several fibrous materials failed to prevent excessive intake. Only unmolassed sugarbeet pulp gave acceptable results, when included at a level of 580 to 650 g/kg. Composition of the fibre appeared to be more important in regulating voluntary intake than fibre concentration of the diet per se. A diet containing a high level of sugarbeet pulp (SBP) had a long transit time and high nutrient digestibility. Nutrient digestibility was influenced by protein level and source. A SBP diet appeared to regulate intake by physical, physiological and metabolic mechanisms. The large volume of wet sugarbeet pulp will increase gastro-intestinal fill. The rate of glucose absorption and secretion of insulin was reduced. A high pre-feeding plasma VFA concentration indicated a more constant supply of nutrients for a longer period after feeding. A SBP diet increased feeding time four-fold. Animals receiving a SBP diet were less active and engaged to a lesser extent in post-feeding oral behaviours. A marked reduction in time spent rooting suggests that the sows were less food-motivated.

The interaction effects of genotype and nutrition on the performance of sows during lactation is still poorly understood; this series of experiments explored the factors contributing to breed differences in lactational performance and the development of appropriate feeding strategies. Two extreme types of sow were used in these experiments; lean pure-bred White sows (W: Large White and Landrace) and a prolific but fatter Meishan synthetic damline (M: 50% Meishan genes). M sows had higher numbers of piglets, a different feed intake curve and produced more milk with a higher fat content compared to W breed types. Their response to dietary protein was different for the two breeds; the Meishan sows, with higher initial levels of body fat reserves, used the extra protein to increase milk production. The White sows did not partition the extra protein into milk but used it to conserve their own maternal body reserves and improved their weaning to conception interval. The breed differences in sows performance were found not to be solely due to differences in litter size or piglet genotype or maternal body fat reserves. M sows showed better maternal behaviour with lower activity and shorter suckling intervals. It can be concluded from these experiments that Meishan synthetic sows are inherently better mothers, and the way in which sows of different breed types partition feed nutrients during lactation is very different. A dietary lysine concentration of 9 g/kg (giving daily intakes of 53-61 g/day at 98-111 MJ DE/day) optimised lactational and rebreeding performance in both breed types.