Twenty-five mature Finnish Landrace × Dorset Horn ewes, each suckling two lambs, were used to measure the effects of dietary concentration of crude protein on food intake, milk yield and changes in body composition during the first 6 weeks of lactation. Diets were complete mixes of milled hay and concentrates, and the amounts of barley and fish meal were altered to give crude protein concentrations of 116 and 143g/kg dry matter. Ten ewes were slaughtered at 5 to 7 days of lactation and the remaining ewes were slaughtered at 40 to 43 days of lactation.

The higher concentration of crude protein in the diet did not alter food intake or digestion. Milk yield was not altered in the first 3 weeks of lactation but was increased in weeks 4 and 5 (P<0·05). Production of milk protein was increased by a higher protein concentration in the diet (P<0·01) and this effect was evident from the 2nd week of lactation. Weight of chemically determined fat in the body decreased from 179 to 13-0kg from 6 to 42 days of lactation (P<0·001) for ewes on diets of both concentrations of crude protein.

It was concluded that the higher level of protein intake during early lactation increased yields of milk and milk protein. The data suggest that the energy lost from the body was used more efficiently by ewes given the diet of high, rather than low, protein content.

The intake of silage, concentrates and grazed herbage, and the performance of 16 Masham ewes carrying and suckling either single or twin lambs, was measured during the last 7 weeks of pregnancy, during lactation and after weaning.

There was no difference in intake between ewes with singles or twins in pregnancy, lactation or after weaning. The metabolizable energy intakes, from silage and concentrates, of the ewes with singles and twins were 101 and 100 MJ per head per day in weeks 7 and 6 pre partum, 21·4 and 19·9 MJ in weeks 3 and 2 pre partum, and 24·4 and 23·8MJ in the 1st week of lactation. The intakes from grass and concentrates were 32·3 and 338MJ in weeks 5 and 6 of lactation for the ewes with singles and twins respectively, and 13·8 and 15 2M J from grass alone after weaning. There was no effect of ewe live weight on intake and, although the ewes with singles were producing less milk than those with twins, their intakes were similar.

The same ewes consistently ate the most feed. The overall coefficient of concordance was 05 6 and the coefficients for mid- and late-pregnancy, late pregnancy and early lactation, and early- and mid-lactation were 0·57, 0·62 and 0·66 respectively. The ewes with twins that consistently ate the most lost less weight in pregnancy, produced similar litter weights and suckled lambs that grew faster. Their levels of intake and production were high: the growth rate from 0 to 6 weeks of age of the twin lambs suckling the large-eaters was 721 g/day compared with 631 g/day for those suckling the small-eaters. During lactation the ewes with singles appeared t o consume more metabolizable energy than their maintenance, milk yield and live-weight gain requirements justified, whereas the group of smaller-eating ewes with twins put on more weight than expected from their intakes.

An experiment was conducted with 84 suckling Scottish Blackface twin lambs on an improved hill pasture with a history of cobalt deficiency and molybdenum/sulphur-induced copper deficiency. The dams of 13 pairs of twins were treated with 90 mg copper at parturition (Cue) and one member of each pair was given a cobalt bullet (Co + ). One member of each of a further 29 pairs was treated periodically with 5 to 15mg copper to maintain plasma copper concentrations >0·6mg/l (Cu+) while their siblings received no supplementary copper (Cu). Fourteen of these pairs also received a cobalt bullet (Co + ). Lambs not treated with cobalt are designated Co−.

The Cue treatment increased milk copper concentrations, but only for a short time, and resulted in transitory increases in lamb plasma copper concentrations and rate of live-weight gain. At the end of the grazing phase, at approximately 20 weeks of age, Cu+ lambs had gained 0-28 kg more weight than Cue lambs and 158 kg more than Cue lambs, and had higher liver copper concentrations. Cu+ and Cue lambs had heavier and fatter empty bodies and carcasses than Cu− lambs. The cobalt treatment produced no effects at this stage.

Fifty-four of the lambs were housed and given dried grass pellets ad libitum. After 83 days liver copper concentrations were higher in Co− than Co+ lambs, and in Cu+ than in Cu− and Cue lambs. The copper treatments had no effect on rate or efficiency of live-weight gain, but Co− lambs gained weight more quickly and more efficiently than Co+ lambs.

Single and twin purebred Scottish Blackface lambs born to Blackface ewes, and Suffolk cross lambs born to East Friesland × Blackface ewes, were removed from their dams at birth and cross-fostered to give all combinations of breed of ewe, breed of lamb and number of lambs suckled, with no ewe rearing her own lamb.

Milk production was measured on 1 day/week for 14 weeks. The effect of ewe breed was significant in all weeks, with the East Friesland cross ewes having a higher peak and a more sustained level of production than the Blackface ewes. Ewes suckling twins produced more milk than those suckling singles. Breed-of-lamb effect was significant during the first 5 to 6 weeks of lactation, with crossbred lambs inducing a higher milk output than Blackface lambs, irrespective of the breed of ewe suckled. Beyond this stage, lactation potential of the ewe replaced demand by the lamb as the first limiting factor.

Food intake by ewes during the first 6 weeks differed slightly with both ewe and lamb breed but there were larger differences associated with number of lambs suckled.

The data suggest that lambs on higher milk intake consume a smaller proportion of solid feed but that, in all groups, live weight at 14 weeks of age was closely related to milk intake.

The development of sexual activity, sperm production, semen characteristics, testis growth and body size was studies in 10 male sheep (ram lambs) of the Romanov breed and 11 of the Finnish Landrace breed between the ages of 4 and 15 months.

The sexual responses, observed daily for 40 days from the age of 4 months, developed earlier and more intensively in the Romanov than in the Finnish ram lambs, being fully developed in the former breed after 4 days as compared with 14 days in the latter breed. All lambs of both breeds, however, were considered capable of impregnating females by 5 months of age.

In both breeds there was a considerable delay between the onset of sexual maturity and the time at which it became possible to collect semen by means of an artificial vagina. Successful collection was not achieved until the age of 11 months, there being no difference between breeds in this respect.

Subsequent semen production increased to the 14th month of age, with little difference between breeds. Respectively for Romanov and Finnish rams at this age (±s.e.), the mean ejaculate volume was 0·85 + 0·062 and 0·77±0·052ml; motility 64·6 ± 1·62 and 59·7±l·66%; sperm concentration 4·75±0·198 and 4·7 ± 0·197 ×1012perl; number of sperm per ejaculate 4 09±0·338 and 3·63 ±0·259 × 109; and fructose concentration 6·84 × 0·2606 and 4·87 ± 0·2707g/1. In the 15th month there was a tendency for these values to decline except in the case of sperm concentration and, hence, total sperm number.

Mean live weight and size increased until the 14th month and there was no difference between breeds, but testis length and diameter were greater in the Romanov rams at this age.

The contribution of fat mobilization to the regulation of fat deposition was investigated in intensively fed, rapidly growing pigs of the breeds Large White and Pietrain. The results indicate that no quantitative differences in fat mobilization parameters existed between the breeds. In both breeds the concentration of non-esterified fatty acids i n blood serum, measured 8h after a meal, was very low, and the fatty acid composition of the non-esterified fatty acids did not reflect the variation in fatty acid composition of the body fat that existed between groups of pigs within each breed. Additionally, the fraction of body fat that was mobilized per day was calculated to be zero for both breeds. It is concluded from these results that the observed differences in fat deposition between Large White (195g/day) and Pietrain (130g/day) were definitely not the consequence of fat mobilization.

Eighty-nine crossbred gilts were used in an experiment to assess the effects of age at puberty on growth and their carcass characteristics at market weight. From 100 days of age each gilt was exposed daily to a boar and observed for standing heat. The gilts were slaughtered in a commercial abattoir as they reached market weight (approximately 109 kg live weight). Thirty-two gilts (36%) reached puberty before slaughter. These 32 earlier-maturing gilts grew more slowly than the other 57 (P<0·001) yet, paradoxically, within the group of 32 which had reached puberty, there was a significant negative correlation between age at puberty and average daily gain (r=−0·565; P<0·001). Of the 32, the date at first oestrus was known in 30 cases. Among these 30, 10 had ovulated more than once (early-maturing) and 20 had ovulated once (intermediate maturing). Consistent with the paradox there was a significant negative correlation between age at puberty and rate of gain within each group but the regression line for the early-maturing gilts had a significantly lower intercept, on the gain axis, than that for the intermediate group (P<0·01). There were no significant differences between sexual maturity groups for any of the large number of physical and chemical carcass characteristics studied.

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.

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.

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.

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.

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.