Eight dietary levels of threonine ranging from 4·8 to 6·6 g/kg air-dry diet were given to 64 growing female pigs from 25 to 55 kg live weight. Results for daily live-weight gain and food conversion ratio indicated a requirement value for dietary threonine of 5·6 g/kg. The pattern of response exhibited by blood urea suggested a requirement of 5·4 g/kg. No clear trends were found for carcass composition or plasma free amino acids

Seventy-two pigs between 7 and 28 days of age were given diets containing milk, fish or soya bean proteins in two separate experiments. In the first experiment, the weight gains of pigs given casein, isolated soya bean protein, fish meal and soya bean meal were 211,180,200 and 191 g/day, respectively, and the food conversion ratios were 0·84, 1·16, 0·93 and 1·10, respectively.

In the second experiment, the protein sources were skim milk, casein, isolated soya bean protein, soya bean concentrate and soya bean meal; weight gains of the pigs on these respective diets were 205, 180, 154, 133 and 169 g/day, and the food conversion ratios were 0·81, 0·92, 0·97, 1·07 and 1·05.

Apparent digestibilities of the soya bean and fish protein diets were less than those of milk protein diets. Apparent digestibilities of all diets increased between the collection periods at 9 to 14 days and 23 to 28 days of age.

Seventy-four Yorkshire gilts, mated at puberty, were used in three experiments to study the effect of severe food restriction, 0·45 kg/day for either the last 15 or 30 days of gestation, on reproductive performance, body-weight change, and carcass quality and meat acceptability. The objective of the experiments was to assess the feasibility of limiting weight gain during gestation to produce an acceptable carcass post-partum, within the market weight range of 55 to 90 kg. Age and weight at puberty averaged 170·3 days and 99·1 kg respectively. Litter size averaged 9·3 liveborn piglets at an average weight of 1·13 kg. The necessary reduction in weight gain during gestation to bring final carcass weight within the acceptable range was associated with a significant reduction in mean individual birth weight to below 1·0 kg. Sensory evaluation of loin and ham joints from mated and unmated gilts of market weight revealed no differences in juiciness or flavour but both loin and ham joints from maiden gilts were significantly more tender than those from gilts that had farrowed and from unmated controls of the same age as those that had farrowed

Individually penned Finnish Landrace × Dorset Horn ewes in early lactation, and each suckling two lambs, were used to test the effects on milk yield, milk composition and the concentrations of some plasma constituents of supplementing a basal diet with either urea, groundnut, soya bean, linseed, fish, meat and bone, or blood meal. The basal diet contained 94 g crude protein and 10 MJ of metabolizable energy per kg dry matter and supplied daily 0·3 MJ of metabolizable energy per kg body weight. Except for urea, which was tested at an inclusion rate that increased the protein (nitrogen × 6·25) content of the basal diet by 43 g/kg, the remaining sources were tested at three levels, corresponding to increases in protein content of 34,60 and 86 g/kg. Daily milk yields were 1·92 and 2·08 kg for ewes given the basal diet and the basal diet supplemented with urea. For the high inclusion rates of each protein source the following daily yields were obtained (kg): groundnut, 2·26; soya bean, 2·45; meat and bone, 2·49; linseed, 2·68; fish, 2·84; and blood meal, 2·91. The daily yields of true protein in milk were (g): basal diet, 76; basal diet plus urea, 80; groundnut, 104; soya bean, 107; meat and bone, 105; linseed, 112; fish, 136; and blood meal, 125. Plasma concentrations of free fatty acids did not appear to support the hypothesis that the milk yield response to protein is accomplished solely by increases in tissue energy loss.

The increment in the amount of non-ammonia nitrogen reaching the abomasum as a result of the low levels of inclusion of the protein sources in the basal diet was used for the production of true protein-nitrogen in milk with an efficiency of 0·58.

Two hundred and forty Suffolk × (Cadzow Improver × Scottish Blackface) female sheep were housed at 4 months of age and average live weight (± s.d.) of 30·6 ± 501 kg, and divided into four equal treatment groups: HH, HL, LH and LL. They were group-fed such that HH and HL sheep were 39·7 ± 5·27 kg, and LH and LL were 35·6 ± 4·64 kg, at puberty, which was recorded in all sheep. There were no differences in average date at puberty.

After puberty the sheep were gradually transferred to different levels of feeding by the time of mating with fertile rams at the second oestrus such that HH and LH were group-fed 1·50, and HL and LL 0·75 of maintenance requirement. The sheep were slaughtered at return or 25 ± 3 days after mating.

The proportion of sheep with live embryos was 0·48,0·40,0·50 and 0·41 for HH, HL, LH and LL groups respectively (NS). Ova wastage was 0·59, 0·68, 0·51 and 0·59 for the treatments, with statistically significant differences in losses between treatments in sheep with two corpora lutea (P<0·05). Ovulation rate also differed between treatments (HH > HL, P < 0·01; HH > LH and LL, P < 0·05). Differences occurred between treatments in the proportion of multiple cycles between first and second oestrus (P<0·05), and HL sheep had a greater proportion of sheep failing to return to service but without embryos (HH>HL, P<0·05). The pooled results showed that pregnant sheep were heavier at 4 months of age (P < 0·05), but not at mating, than non-pregnant sheep. Sheep with two corpora lutea were more likely to be pregnant than sheep with one corpus luteum (P < 0·05).

An unselected, non-inbred population of laboratory mice has been propagated for 25 generations by 20 pairs (families) of mice, each leaving one son and one daughter selected at random from the litter. The daughter was given the family number of her dam, while her mate came from another family varying systematically in different generations. The breeding plan precluded any possibility of common ancestry for five generations. In later generations the inbreeding coefficient rose at an average rate expected from a population with an effective number of approximately 80, to approximately 0·13 in generation 25. The rise occurred in cycles, repeating every five generations. Data are presented to demonstrate that overall reproduction (total weight of young produced at 9 weeks of age, per female mated) and the components of survival from birth to 9 weeks, survival from sexing (3 weeks) to 9 weeks separately for males and females, and 9-week weight of males and females, were each sensitive to changes in inbreeding coefficient. In contrast, conception rate, litter size (live young born) and sex ratio did not reflect changes in the inbreeding coefficient. The magnitude of the depression in overall reproduction was substantially greater than that in any of the affected components.

Forty-four British Friesian, first-lactation heifers were used in a randomized block experiment over a 2-year period to examine the effects of two patterns of concentrate allocation during the post-calving, indoor feeding period. The animals, mean calving date 17 October (s.d. 15 days), were offered concentrates either on a high-low system consisting of 80kg/day for the first 90 days of lactation and thereafter 5-4kg/day, or on a uniform system in which 6-8 kg/day was offered from calving until going to pasture (mean of 182 days). In addition, all animals received access ad libitum to grass silage, with a mean dry-matter content and digestible organic matter in the dry matter value of 218 and 679g/kg respectively. During the 1st year all 22 animals were housed as a single group, but in the 2nd year the animals were housed in individual stalls and silage intakes recorded for all replicates. In each year all animals grazed as a single group at pasture without supplementary concentrates.

Total concentrates consumed were 1163 and 1187 (s.e. 19·4)kg for the high-low and uniform treatments respectively. Although the animals on the high-low treatment reached a higher peak milk yield, there were no significant differences in milk yield over the winter period, 3257 and 3311 (s.e. 41·5) kg, or total lactation, 4862 and 4886 (s.e. 80·6)kg, for the high-low and uniform treatments respectively. The animals on the high-low treatment, however, were significantly lighter in body weight at the end of the winter but there was no difference between treatments at the end of lactation. Milk composition data are also presented.

In each of 2 years, two groups of 25 British Friesian heifers were given, respectively, a moderate- and a low-energy diet for a 12-week period. Mean live-weight gains of 0·25 kg/day and 0·45 kg/day were recorded for the moderate-energy diet, and losses of 0·22 kg/day and 013 kg/day for the low-energy diet. Heifers were inseminated artificially at oestrus at approximately the mid-point of the 12-week period, this oestrus being the next observed after synchronized oestrus, which followed luteolysis induced by cloprostenol injections. With few exceptions, heifers that gained weight were in good or medium condition at insemination and those that lost weight were in medium or poor condition.

Highest pregnancy rate (0·78) was recorded for heifers that gained weight and were in medium condition at insemination. For heifers losing weight, pregnancy rate dropped to 0·46 (P < 0·05) due to reproductive failure occurring before the 25th day after insemination. Only in heifers in poor body condition was there a significantly higher proportion failing to ovulate normally (P < 0·001). Among heifers gaining weight, those failing to become pregnant to the first insemination were approximately lOOg/kg heavier than the pregnant ones (P<0·05).

Irrespective of gain or loss of weight, and of body condition at insemination, embryo losses did not occur later than the 25th day after insemination, except that five heifers that showed oestrus when pregnant (according to plasma progesterone levels) and were reinseminated then showed evidence of embryo loss.

In each of 4 years, 24 autumn-calving, single-suckling Aberdeen Angus × Friesian cows with Charolais cross calves were subjected to different winter feeding regimes and to a range of weaning dates, and the effect on cow and calf food intake and performance was measured. Giving 257 kg concentrate dry matter to cows on an ad libitum silage diet over winter increased calf and cow weights in the following September by 17·8 and 11·7 kg respectively. Weaning after 4 months of lactation resulted in a net saving in winter forage requirements when compared with weaning in March/April but a high input of concentrate was necessary to achieve satisfactory calf performance. Weaning in July increased calf weights in August/September by 22·1 kg and reduced cow weights by 22·3 kg compared with weaning in March/April. Later weaning at pasture might be preferable, producing heavier calves, provided that cow weights can be restored at pasture.

Samples of cooked muscle of Swamp buffalo, Hereford, Angus, Friesian and Charolais cross steers were sheared and scored by a taste panel for tenderness, flavour, juiciness and palatability. The cattle were given commercial pellets from 9 months of age to slaughter at 12,15 and 18 months. The buffaloes were fed one of four regimens: all pellets, all hay, 3/4 pellets and 1/4 hay or 1/4 pellets and 3/4 hay from 13 to 22 months of age to slaughter at 20 to 34 months.

There was little difference between the buffaloes and the cattle in shear-force or taste panel scores. Age at slaughter had no significant effect on the quality traits measured in either the buffaloes or the cattle. The feeding regime did not influence the tenderness, flavour or palatability of buffalo muscle but the high pellet diets increased juiciness.

Shear-force was not influenced by rectal or muscle temperatures, muscle pH, carcass weight or fatness in the buffaloes but fatness reduced shear-force in cattle m. longissimus.

Buffalo intramuscular fat increased with age and carcass fatness but had no effect on shear-force or taste panel score.

Body weights at birth, 90 days, 180 days and 1 year of age were analysed in 620 calves, the offspring of sires of the Friesian, Jersey and Simmental breeds, and of dams of three indigenous zebu breeds, namely Barka, Boran and Horro, at four diverse locations in Ethiopia.

Breed of sire, breed of dam and location all significantly affected weight. Progeny of Friesian and Simmental sires were similar in weight but both were heavier than the progeny of Jersey sires, their weight being, respectively, 25·0,24·9 and 21·2 kg at birth; 88·0, 84·6 and 74·9 kg at 90 days; 151·7, 150·6 and 135·4 kg at weaning at 180 days; and 220·6,224·8 and 193·3 kg at 365 days. Barka crosses were heaviest and Horro lightest. Mean weight for progeny from Barka, Boran and Horro dams was, respectively, 24·0, 24·6 and 22·5 kg at birth; 85·2, 83·8 and 78·5 kg at 90 days; 149·6, 148·0 and 140·1 kg at 180 days; and 233·7, 208·1 and 196/9 kg at 365 days. Dam breed × location interaction was significant except at birth, and sire breed × dam breed and sire breed × location interaction were significant at 90 days of age. In a comparison of Friesian and Simmental, the Friesian sires interacted relatively more favourably with the Barka dams, and the Simmental with the Boran. The Jersey was also relatively better with the Boran crosses, compared with either the Barka or the Horro crosses. By 1 year of age Jersey crosses were at a relative (but insignificant) advantage in body weight at the hottest location.

Two experiments have been conducted to compare wilted, formic acid-treated red clover and unwilted, formic acid-treated grass silages for beef production, and to examine the effects of digestibility of red clover and level of concentrate supplementation on food intake and animal performance.

In experiment 1, 12 groups of four British Friesian steers (initial live weight 229 kg) were given red clover silages of high and low dry-matter digestibility (0·70 and 0·60 respectively) and grass silage (0·71) ad libitum for a period of 11 weeks. Silage dry-matter intake and live-weight gain for the steers given red clover of high digestibility, red clover of low digestibility and grass silages were 7·75, 0·89; 6·91, 0·69; and 5·59, 0·59 kg/day respectively.

In experiment 2, 12 groups of four British Friesian steers (initial live weight 332 kg) were given red clover silage with a dry-matter digestibility of 0·63 and grass silage with a value of 0·76 ad libitum, either unsupplemented or supplemented, with 2 kg/day of fortified barley per head for a period of 19 weeks. Silage dry-matter intake, live-weight gain and carcass gain were 8·52, 0·63, 0·32 and 6·98, 0·78, 0·43 kg/day for the unsupplemented and supplemented red clover silage treatments, and 6·82, 0·59, 0·31 and 5·75, 0·75, 0·44 kg/day for the unsupplemented and supplemented grass silage treatments respectively. The performance of the cattle offered red clover silage was similar to that of cattle offered grass silage of 0·12 higher digestibility, largely as the result of higher dry matter intakes achieved on red clover silage.

Ninety-six Hereford steer calves that weighed 249(s.e.4·7)kg were allocated randomly to four treatments of 24 steers each in a randomized complete block design with four blocks. The steers grazed dormant native range forage that contained 41 to 60 g of crude protein per kg dry matter during the 120-day wintering trial and were given 0·91 kg of supplement per head per day. The supplements used contained 175 or 350 g crude protein per kg dry matter and 0 or 165 mg monensin per kg supplement; a factorial arrangement of treatments was used in allocating the supplements. Weight gains of steers given the high-protein supplements were greater than those on the low-protein supplements during periods 1(0 to 61 days) and 2 (62 to 120 days), and over the total trial (P < 0·01). Monensin increased weight gains during period 1 and the total trial (P < 0·01). The protein level × monensin interaction was not significant for either period or the total trial (P > 0·15). The results indicate that inclusion of monensin in protein supplements for growing cattle grazed on low-quality dormant native forage may allow some reduction in protein content of the supplement.

Two trials were conducted at the BOCM Silcock Development Unit at Stoke Mandeville. The first trial evaluated the response on doe and progeny, from mating to 8 weeks after parturition, of rabbit compound diets containing 0, 100, 200 and 300 g sodium hydroxide-treated straw per kg. Performance data showed no detrimental effect of inclusion levels up to 300 g sodium hydroxide-treated straw per kg despite its high sodium concentration.

A second trial was made to ascertain whether these findings were due to the treated straw itself or to increasing sodium concentrations. A standard rabbit compound diet containing 2·5 g sodium per kg was compared with diets containing either 5·0 or 10·0 g sodium per kg, and with experimental compound diets containing either 80 g sodium hydroxide-treated straw or 80 g untreated straw per kg and both containing 2·5 g sodium per kg. Peak food conversion was estimated to occur at a dietary sodium concentration of 4·6g/kg, although the slope of the dose response curve was not statistically significant at the P ≤ level.

The results indicate that compound diets containing up to 80 to lOOg sodium hydroxide-treated straw per kg may be fed to rabbits and that inclusion of levels of up to 300 g sodium hydroxide-treated straw per kg are not detrimental to performance. On the other hand, an inclusion of 80 g untreated ground straw per kg in compound diets for rabbits had a growth-depressing effect.