During the period 1974-77 six blocks of a perennial ryegrass/white clover sward were each divided into two for rotational paddock-grazing and silage cutting in alternate years. For each use an annual total of 360 kg nitrogen per ha was applied. Six livestock treatments of cattle only or cattle and sheep were grazed on the blocks. The stocking rates per ha and combinations of cattle (yearling steers) and sheep (ewes nursing twin lambs) respectively were low, 7·5 + 0; medium, 10 + 0, 7·5 + 5, and 5+10; and high, 7·5 + 10 and 5 + 15.

The annual quantities of herbage organic matter accumulated (6·6 to 7·2 t/ha) and consumed (5·6 to 6·7 t/ha) did not differ markedly according to grazing treatment during an individual year, nor was there an effect on organic matter accumulation in subsequent conservation years (11·3 to 12·0 t/ha). Between-year effects were significant. As judged by persistence of sown species there was no evidence of sward deterioration over the 4 years.

Total live-weight gain per ha increased with increasing stocking rate but with a decreasing increment. The ranges were 106 to 1·42 t/ha within treatments, 102 to 1/45 t/ha within years and 0·97 to 1·8t/ha within treatments × years. Individual gains of cattle (0·67 to 0·88 kg/day) and lambs (0·20 to 0·27 kg/day), and the proportion of lambs ready for slaughter (0·53 to 0·97), were lowest at the highest stocking rate. Mixed grazing compared with cattle-only led to improved cattle gains and improved total gains per ha. The benefits of mixed grazing for a species tended to increase as the proportion of that species in the mix decreased.

Estimates of dam reproductive performance are reported for purebred Africander, Angoni, Barotse and Boran dams, and the reciprocal crossbreds of the latter three breeds, under ranching conditions in Zambia.

Mean performances based on a maximum of 1996 records collected over six parities were: calving rate, 65·6%; weaning rate, 62·8%; calf birth weight, 26·6kg; calf weaning weight, 163·6kg; and dam live weight at weaning, 363 0 kg.

Purebred Africander and Barotse dams had significantly poorer calving rates, 542 and 57·6% respectively, than the purebred dams of the Angoni and Boran breeds, 69·1 and 66·0% respectively. Reciprocal crossbred dams of the latter two breeds had the highest calving rates, 71·2 and 74·4%. Heterosis estimates for calving rate were 0·8% for Angoni/Barotse crosses, 7·8% for Angoni/Boran crosses and 10·3% for Barotse/Boran crosses and, for weaning rate, 3·7, 6·7 and 11·5% respectively. There were no differences between reciprocal crossbred dams for calving and weaning percentages. The mortality rate of calves born to crossbred dams was 40% and that of the calves born to purebred dams of the same breeds 4·7%. Dam status at mating had an important effect on fertility with the calving rate of dams dry at mating, 89·1%, contrasting with a rate of 39·8% for those dams that were lactating at mating and that had calved late in the season.

There were large differences between breeds for calf weights but heterosis estimates were small and nonsignificant. There were no differences between the progeny weights of reciprocal crossbred dams. Sex, date and period of birth, and dam status had significant effects on calf weights.

Africander dams had the heaviest, and Angoni dams the lightest, live weights at weaning, 421·1 and 320·7 kg respectively. Heterosis estimates for dam live weights were small and non-significant, and reciprocal crossbred differences were unimportant. Dams which lost most live weight during the dry season, that had extremely light live weights at the beginning of the breeding season or that gained little weight during the breeding season had significantly poorer fertility than other dams.

Overall estimates of heritability derived by dam/daughter regression were 0·20 for calving percentage, 0·76 for calf birth weight and 0·72 for calf weaning weight.

A series of trials was conducted to measure the extent of individual variation in feedblock intake for ewes on upland/hill farms. From 15 flocks on nine farms 4284 ewes were selected with a range of environmental conditions and levels of performance. Ewes were given either Rumevite, Norbloc or Wintawell feedblocks containing chromic oxide. Faecal grab samples were taken per rectum from individual ewes and analysed for their chromium content to obtain estimates of feedblock consumption.

The results showed that provision of feedblocks does not ensure a uniform intake of supplementary nutrients by sheep in upland/hill situations. On average, 19% of the 2931 ewes sampled had not eaten the feedblock on offer. The proportion of ewes not consuming feedblock varied from flock to flock (0 to 67%). The coefficient of variation of faecal chromium concentrations varied between flocks (46 to 231%). The reasons for the large variation in intakes observed are discussed. Feedblock intake was significantly affected by the grazing area per ewe (P<0·01) and the age of ewes (P<0·05 to P< 0·001).

1. Four groups of British Friesian heifers born in April (no. = 30), July (no. = 29), October (no. = 30) 1977 and January 1978 (no. =27) were allocated to one of six treatments (planes of nutrition) at a mean age of 91 days. From 91 to 365 days of age heifers on treatments 1 to 5 were given individually, according to body weight, a proprietary pellet to 126 days of age, and thereafter a diet of dried lucerne and barley. Heifers on treatments 1 and 2 were fed at the same rate whereas heifers on treatments 3 to 5 were fed at successively higher rates. Heifers on treatment 6 were fed ad libitum the proprietary pellets to 126 days of age and thereafter a 'barley beef diet. Mean live-weight gains between 91 and 365 days of age for treatments 1 and 2 combined and 3 to 6, respectively, were 0·58, 0·68, 0·75, 0·82 and 1·06 kg/day.

2. Plasma progesterone concentrations were determined twice weekly in each animal. Puberty was assumed to have occurred 2 days before the start of the first period in which the progesterone concentration exceeded 1μg/1 for at least 10 days.

3. There was no significant difference between treatments in mean body weight at puberty (242 kg), but age at puberty (347, 305, 288, 301 and 239 days for treatments 1 and 2 combined and 3 to 6, respectively) was inversely related to rate of live-weight gain between 91 and 365 days of age. However, within each treatment group the fastest growing heifers reached puberty at the same age but at a heavier body weight than the slowest growing heifers.

4. There were significant seasonal effects on age and body weight at puberty. The most rapidly reared animals (treatment 6) born in January and April were, on average, 52 days younger and 54 kg lighter at puberty than those born in July and October, but the effects of season of birth in other treatments were different.

5. There was no significant difference between treatments in the number of conceptions (mean 0·67) achieved at first service by an Aberdeen Angus bull introduced when the heifers were 350 days of age.

Twenty-two unmated female Ayrshire twin cattle, that had initially been maintained for prolonged periods on one of six constant feeding levels until an equilibrium weight was attained, were subsequently moved up to higher constant feeding levels including ad libitum. In all, results were obtained for 44 equilibrium periods mostly of 96 weeks duration.

For controlled feeding levels, the log-log,. regression of equilibrium body weight on food intake, within animals, was 0·999 (s.e. 0·045). For all results, including mature equilibria, the within-animal regression was 1–014. There was thus no systematic change in an individual's equilibrium maintenance requirement per kg body weight in the range from 25%, to 100%, mature. Efficiency of food utilization for equilibrium maintenance was found to be independent of age also, except for a small increase at advanced ages beyond 8 to 9 years.

There were significant differences between animals in equilibrium maintenance efficiency, the genetic coefficient of variation being 6·4%. The most striking result, however, was a within-animal repeatability of 0·7, which meant that almost the same efficiency was re-attained when, after a prolonged period of many years on one constant feeding level, the same animal was allowed to re-establish a new equilibrium on a higher level.

Following prolonged periods of food restriction, the animals showed remarkable capacity to recover in body weight even at very advanced ages, but nevertheless substantial stunting of mature weight did occur.

1. The ability to resist hypothermia was measured in 265 lambs of 10 breeds immersed in a progressively cooling water bath.

2. Cold resistance varied significantly between breeds, with hill lambs showing the highest resistance. Hill breeds and feral breeds together had the highest weight-specific cold resistance.

3. Cold resistance was positively correlated with birth weight and skinfold thickness.

4. Age at test varying from 1 to 60 h did not significantly affect cold resistance.

5. Rate of recovery from hypothermia varied slightly between breeds. The feral lambs tended to recover fastest.

The effects of the lactation, pregnancy and calendar month on monthly milk records of 1st and 3rd lactation Israeli-Friesian dairy cows were studied. The analyses involved 717 966 monthly records in 76 788 lactations of cows diagnosed as pregnant in herds providing 20 or above lactations per herd per year and lactation number. The records were grouped into 18 lactation classes according to yield post partum: high, medium and low cows within high, medium and low herds, separately for 1st and 3rd lactations.

The objects of the investigation were to estimate factors for relating persistency to peak yield, and to examine how interactions between peak yield and persistency should be taken account of in post partum breeding policies.

The major factor affecting yield was the number of months post partum; heifers dropped in yield by 0·173 from the 1st to the 10th month of lactation and cows by 0·46. The herd level affected the shape of the lactation curve. In high-yielding herds peak yields were achieved later than in low-yielding herds, but the rates of yield decline from the 2nd to the 10th month were similar in high- and low-yielding herds. Within herds, there were large differences in the rate of decline between cows with high and low peak yields. The monthly decline within herds from the 2nd to the 10th lactation month for animals of high and low peak yield were –0·0347 and –0·0217 for heifers and –0-0633 and –0·0520 for cows.

Effects of pregnancy on milk yields were observed from the 1st month post conception, but the effects were small. The effects of 7 months of pregnancy on test-day yields were 3 to 4 kg milk, independent of the yield level of the cow. It was suggested that the effect of herd level could be disregarded but that account should be taken oflactation number and the yield level of the cow within her herd. Heifers and cows in high-yielding herds may be mated later than cows in low-yielding herds. Since pregnancy had a similar effect on high- and low-producing cows, and within herds the higher yielding cows were less persistent in yields than the remainder, it might be a reasonable management policy to breed most of the cows in a herd of a particular lactation at approximately the same time post partum.

Data were extracted from Meat and Livestock Commission records from 44 herds with 392 progeny-tested sires in both farm and station environments. The farm data contained 4182 and 17 251 male and female progeny respectively, and the station data 2982 and 1490 male and female progeny respectively. Both sets of data were adjusted separately for the effects of month of test within sex. The farm data were also corrected to a constant end-of-test-weight corresponding to that at the station. Comparisons were made between both different and the same sexes in the two environments. Phenotypic correlations between a simple index measure in both environments ranged from +0·20 (farm females:station males) to +0·30 (farm females:station females). Genetic correlations between similar traits ranged from –018 (weight/age, farm males:station females) to +081 (simple index, farm males:station females). The correlations between female farm progeny and station male progeny were generally lower than for any other comparisons.

The follicle population of 44 purebred 20-month-old Corriedale ewes and rams was examined for effects due to sex and birth status. Twin birth resulted in a lower ratio of secondary to primary follicles at 20 months of age in these medium follicle-density animals. This effect is similar to that reported for the high follicle-density Australian Merino. Similarly, the ewes had a lower ratio of secondary to primary follicles than the rams.

Nine bulls of the Spotted Slovak breed were exposed to different stressful stimuli. The stimuli used were noise, electric shock and the administration of insulin, adrenocorticotrophic hormone and the sedative xylazine (Rompun). The levels of glucocorticoids, free fatty acids and glucose were determined in blood samples obtained through a permanent, indwelling, jugular cannula. It was found that insulin, adrenocorticotrophic hormone and electric shock evoked significant increases in the concentration of glucocorticoids in the blood. Noise did not affect the blood level of glucocorticoids. The stimuli did not induce any change in the blood levels of free fatty acids. Blood glucose levels were increased following insulin, adrenocorticotrophic hormone, electric shock and xylazine but not following noise. Insulin, as expected, decreased the concentration of glucose in the blood.

Ninety-six lactating British Friesian cows were offered ad libitum two grass silages having the following analyses: 181 and 241 g dry matter per kg fresh weight, 108 and 96g digestible crude protein per kg dry matter and 617 and 619 g digestible organic matter per kg dry matter. In addition, four concentrate supplements were offered, containing either 360 g crude protein per kg on an air-dry basis and given at the rate of 015 kg/kg milk or 180 g crude protein per kg given at the rate of 030, 0375 and 0·45 kg/kg milk. Large and highly significant differences were recorded in silage intake, mil yield, milk composition, live weight and condition score during the winter feeding period. These differences in performance were associated more with differences in energy than in protein intake. During the post-experimental grazing period no significant differences between treatments were recorded in milk yield and composition, with the exception of fat concentration, and by midsummer no significant differences were apparent in live weight. The results of the experiment were appraised in economic terms and implications for commercial practice discussed.

Total teat number in a Large White and a British Landrace population had a modal number of 14. The trait was highly leptokurtic, indicated by the fact that 086 of the population falls within one standard deviation of the mean. There was no sex difference in total teat number, although a small but significant breed difference existed. Heritability of the trait was low, of the order of 0·10 to 0·20 based on the sire component of variance. Larger dam terms suggested a maternal effect.

Severely inverted teats (nipple invisible) were observed in 0·17 of gilts. Mean number of inversions was 0·738 in the entire population but 4·01 in affected gilts. The heritability of the trait was of the order of 0·20 and a maternal component was possibly involved.

Inverted teats are not distributed at random. They occur most frequently in the umbilical and anterior regions and diminish sharply in frequency towards the rear. In this study 0·97 of all affected pigs had one or more inverted teats in the umbilical and anterior regions.

The postural behaviour of a group of 12 pigs in a pen was studied whilst the air temperature was varied, all physical variables except pig weight being held constant. The air temperature was varied between −4°C and + 5°C of the theoretical lower critical temperature. The range of live weight was from 30kg to 75 kg. An indication of whether the pigs were above or below their lower critical temperature was obtained from the amount of huddling. Pigs of less than 45 kg live weight had a greater tendency to modify their environment by altering their posture. Measurements of floor-area covered showed that pigs over 50 kg live weight occupied an area approximately equal to the recommended minimum whilst smaller pigs occupied up to 20% less area than that recommended, depending upon the temperature: this was due to the tendency of smaller pigs to lie on top of each other when cold.

Forty-eight Large White × Landrace weanling pigs weighing initially 9·69 (s.e. 013) kg were used to evaluate the dietary methionine requirements of weanling European pigs reared under a humid, lowland, tropical environment. Response criteria used were growth rate, efficiency of food conversion, carcass quality, and the weights of some organs and individual muscles. The pigs (three male castrates and three females per treatment) were given a cassava flour-soya bean meal diet containing 202 g crude protein per kg dry matter and supplemented with increments of multiples of 0·8 g DL-methionine per kg diet. Total dietary methionine levels ranged from 2·3 to 7·9 g per kg diet dry matter. All diets contained 14·75 MJ digestible energy per kg dry matter. The experiment lasted 42 days, at the end of which the pigs were slaughtered at an average live weight of 17 kg.

Growth rate and feed efficiency were significantly improved when the basal diet was supplemented with DL-methionine (P< 0·001). No significant treatment differences in organ weight were found. Methionine requirement was significantly influenced by sex and age of the pigs, with castrates having lower requirements than females. Pooled estimated methionine requirements for optimum growth rate and efficiency of food conversion were 4·0 and 4·3 g/kg diet dry matter respectively. Maximum proportion of lean was recorded on the diet containing 3·1 g total methionine per kg dry matter.

1. Two trials were carried out to investigate the effects of high-copper supplementation of isonitrogenous diets containing either white-fish meal or soya bean meal as the sole protein supplement.

2. There was no difference in performance between the two diets when they were fed unsupplemented with copper in trial 1. The addition of 250 mg copper per kg diet significantly and similarly improved performance on both diets.

3. Liver-copper stores, but not kidney-copper stores, were significantly increased when the copper-supplemented diets were fed. The level of the liver-copper stores on the soya bean meal supplemented diet was, however, some 400g/kg less than that on the white-fish meal supplemented diet. The significance of this clearly established finding is discussed.

Eight Angus cross and eight Charolais cross steer calves (out of Hereford × British Friesian cross dams) were weaned at turnout when 7 months old. Over a summer grazing period of 182 days these ‘early-weaned’ calves grew 30 to 35 % slower than eight comparable steer calves of each cross which continued to suckle their dams until 11 months of age. At housing, the early-weaned calves were 100 g/kg lighter, but this difference had no effect on growth rates or silage intakes during the 138-day finishing period. At the same age early-weaned steers had reduced hot carcass weight and dressing percentage but a similar proportion of fat in the forerib joint.

In a trial to evaluate the growth of crossbred calves under semi-arid ranch conditions in Botswana, pure Tswana and crossbred beef cows were inseminated with Beefalo and Italian semen or mated naturally with Brahman, Simmental or Tswana bulls. The 424 calves produced were weighed at birth and at monthly intervals t o 18 months of age.

Beefalo crossbred calves were significantly lighter at birth than all other calves (P<0·05). At weaning (7 months) Brahman-sired calves were significantly heavier than Tswana calves, but no heavier than the other breed types. At 18 months of age Brahman, Italian and Simmental crosses were all significantly heavier than Tswana calves (P<0·05), but there was no significant difference between Beefalo crossbred and pure Tswana calves.

These results indicated that the Beefalo cross had no advantage over the indigenous Tswana breed and more-conventional breeds were superior when crossed with the Tswana.

Carcass data for a total of 1385 pigs from years 3 to 6 of the Meat and Livestock Commission's Commercial Pig Evaluation were used to examine the value of different shape assessments as predictors of carcass composition, when used in addition to carcass weight and fat thickness over the m. longissimus at the head of the last rib (P2). The sample comprised pigs from 13 breeding companies and a purebred Large White control.

The standard deviation of carcass lean proportion at equal weight and P2 was 24·5 g/kg. The addition of carcass length or visual conformation assessments (five-point scales) provided a small improvement in precision (minimum residual standard deviation = 24·2 g/kg). This improvement was associated with a reduction in the variation of lean to bone ratio.

The addition of an effect for breeding company to weight and P2 improved the precision substantially (residual standard deviation = 23·1 g/kg). The improvement was due mainly to the identification of differences in carcass fat content, there being a range of 30g/kg in carcass fat content between companies at equal weight and P2.

There was a further small improvement in precision from the addition of conformation assessments to weight, P2 and company (minimum residual standard deviation = 22·9 g/kg).

The study confirms earlier results which indicate that shape assessments are of limited value as predictors in the British pig population, due mainly to limited variation in lean to bone ratio. It also indicates that significant variation exists between companies in fat content at equal P2 and weight which is not explained by shape assessments.

A basal diet containing 120 g crude protein per kg and 9g lysine per kg, and previously shown to be limiting in one or more essential amino acids and/or non-essential nitrogen, was examined. It was fed either alone to growing female pigs from 25 kg to 55 kg live weight or in combination with four supplements of synthetic amino acids each containing three out of isoleucine, methionine, threonine and tryptophan. A control diet containing 140 g crude protein per kg and 9g lysine per kg was also included. Blood samples were collected at 40 kg live weight in order to examine the influence of dietary treatments on blood metabolites. Results for growth performance, carcass composition and blood urea indicated that threonine was the first limiting amino acid in the basal diet. Plasma free amino acids gave no clear trend. Growth performance and carcass composition were unaffected by supplementation of the diet with glycine indicating that the dietary supply of non-essential nitrogen was adequate.

The relationship between litter size at birth and litter weight at weaning is curvilinear, with an intermediate litter size resulting in the heaviest litter weight at weaning. Relative to feral mice, the mean and variation for litter size at birth was larger for domesticated mice which had been selected for fertility and crossbred. Consequently, some of the litters from the crossbred domesticated mice were larger than the litter size at birth which optimized litter weight at weaning, primarily due to increased pre-weaning mortality. If litter weight at weaning is to be optimized by indirect selection for litter size at birth, the variation around an intermediate optimum litter size at birth could be most effectively reduced by negative assortative mating.