Heritability or the genetic regression of one trait on another, for example live-weight gain in field v. performance test station conditions, can be estimated efficiently by rearing offspring only from high- and low-ranking individuals, and estimating the regression of offspring on parent performance. Formulae are given for the optimum proportion of available animals to select as parents when the relative numbers of individuals in the parent and progeny generation are fixed. Although the optimum depends on the value of the parameter to be estimated, the designs are very robust to poor estimates.

1. Three experiments have been carried out to study the effect of adding trichloroethyl adipate, a compound known to prevent the production of methane both in vitro and in vivo, to the diet of sheep on fermentation in the rumen and on the growth of lambs. In Experiment 1 the additive was incorporated at various levels for 6 weeks, in Experiment 2 it was given at one of four levels for 12 weeks and in Experiment 3 it was included in the food of growing lambs for 15 weeks.

2. Initially, in Experiments 1 and 2, the additive caused a large reduction in methane production and in the molar proportion of acetic acid in the rumen liquor with a corresponding increase in propionic acid. These effects were much reduced after the first 2 to 3 weeks of administration.

3. The total food intake of the animals receiving the additive in Experiment 3 was 4% less than that of the control animals. This difference was negligible at the start of the experiment but increased throughout the feeding period.

4. On average, the relative live-weight gain and the changes in the weights of carcass, viscera and empty body weight of the animals receiving the additive were also 4% less than those of the control animals.

5. The observed differences in weight gain resulted from the differences in food intake and the additive had no beneficial effect upon lamb growth. This lack of effect on growth was due to rapid adaptation by the rumen fermentation to the presence of the additive.

The possibility that embryo survival in a breed of sheep may be related to the number of embryos normally present after natural mating was investigated by transferring large numbers of embryos to sheep of breeds with an approximately two-fold difference in ovulation rate. When the same number of embryos (14) was transferred to each of 12 Scottish Blackface and 11 Finnish Landrace ewes survival was greater in the Finn ewes (10%) than in the Black-faces (4%). The survival of 28% of embryos when transferred in groups of 7 to each of 14 Scottish Blackface ewes indicated that survival was not similar in the two breeds when the number of embryos present was a similar multiple of their natural ovulation rates. When the number of embryos transferred to Scottish Black-face ewes increased from 7 to 14 the decline in survival rate was so great that the number of lambs born also declined, indicating an intermediate optimum ovulation rate for maximum litter size.

The reproductive performance of 51 Finnish Landrace × Dorset Horn (FD) ewes was compared with that of 50 Border Leicester × Scottish Blackface or Greyface (GF) ewes. Ewes were mated without hormone synchronization in November 1973 and with hormone synchronization in August 1974 and again in February 1975. Conception rates at the three matings were 88, 82 and 73% respectively in FD ewes and 96, 56 and 26% respectively in GF ewes. Mean litter size over three lambings was 2·34 in FD ewes and 2·15 in GF ewes. Stillbirths accounted for 12·0 and 10·2% of all lambs respectively and further lamb deaths during and after birth were 15·2 and 4·3% respectively; 11·6% of live FD lambs and 7·7% of GF lambs were fostered or reared artificially. The losses resulted in mean numbers of lambs weaned per ewe lambing of 1·75 from FD ewes and 1·85 from GF ewes (including lambs from those ewes that were artificially reared). Annual productivity was 2·13 and 1·67 lambs respectively.

Three mature rams in each of four naturalized breeds (Romney, Border Leicester, Cheviot and Dorset Down) and two or three 15-mo-old rams in each of four recently imported ‘exotic’ breeds (Finnish Landrace, East Friesian, German Whiteheaded Mutton and Oxford Down) were mated to between 14 and 32 Romney ewes in a pedigree pen-mating system at Mana Island, New Zealand. Two or three 60-min observations of mating behaviour were made on each ram.

There were no significant differences in mating behaviour scores between groups of breeds, but the mature rams of the naturalized breeds were more fertile than the young rams of the exotic breeds (76% and 57% ewes not returning to first mating respectively). Within the young exotic breed group there were significant differences between breeds in number of serves per test, interval to first mount and fertility. Fertility was negatively correlated with time to first mount.

Voluntary intake of a range of feeds by cows is predicted on the assumption that the cows will satisfy their energy requirements unless physical limitations intervene. Predicted patterns of intake throughout lactation agree generally with observed changes, including an eventual plateau in body weight due to a predicted physical equilibrium between abdominal fat and gut contents. An attempt to incorporate a depression in milk yield when physical limitations prevented energy requirements being met by food intake was successful only with good quality feeds.

Teat canal stretchability was measured on 119 lactating cows from two dairy farms, using a probe. Diameter of one hind teat was measured by calipers at the proximal end of the teat and 20 mm above its distal end. Teat canal stretchability, teat diameter at the proximal end and teat diameter gradient were highly correlated with milk yield. Cows with higher teat diameter gradient (i.e., funnel-shaped teats) had higher teat canal stretchability values compared with the cows with lower teat gradient values (i.e., cylindrical teats). Stretchability of the hind teat canal was significantly greater than the stretchability of the fore teat canal.

The feeding value of four batches of dried lucerne cobs was compared in two experiments with beef cattle. The cobs were prepared from primary growths, cut early (LI) and late (L2), and from second-cut (L3) and third-cut (L4) material.

In Experiment 1, intakes and digestibilities of the four cuts, offered as the sole feed, were measured using six British Friesian steers in two (3 × 3) Latin squares. The intake of lucerne cobs decreased as the digestibility of organic matter and cellulose increased, to result in similar intakes of digestible organic matter for all treatments.

In Experiment 2, 32 beef cattle were given rolled barley and the lucerne cobs in the ratio of 1: 2 at two levels, plus barley straw ad libitum. The treatments were compared in eight (4 × 4) Latin squares. Similar daily gains were supported by diets containing LI, L3 and L4. Performance on diets containing L2 was significantly poorer at both levels of feeding.

Two 7 × 7 Latin square experiments were carried out with British Friesian steers (mean initial live weight 360 kg). In Experiment 1 the effects of different levels of dried grass or concentrate on the intake of silage dry matter (DM) were compared, and in Experiment 2 the effect of a supplement containing various proportions of dried grass: concentrate on the intake of silage DM was examined. In both experiments the digestibility of the ration and the rate of passage of digesta were measured.

In Experiment 1, supplementation depressed intake of silage DM, the difference being significant (P<0·05) at 5·0 and 7·5 kg/day, but there were no significant differences in silage intake between supplements given at the same level. Intake of silage was also significantly lower (P<0·05) in Experiment 2 when a supplement was offered, but differences between supplements were not significant. Total DM intake was increased significantly (P<00·5) by supplementation in both experiments. Supplementation increased energy digestibility but decreased crude fibre digestibility. In Experiment 1 nitrogen digestibility was significantly lower (P<0·05) with dried grass than with concentrate supplementation, but in Experiment 2 supplementation increased the digestibility of nitrogen. In both experiments the mean retention time was shorter, the time for the highest rate of excretion of stained particles was lower, and the maximum rate of excretion higher for dried grass than for silage.

1. A total of 74 energy balance trials was made with five Hereford × British Friesian bulls and five steers raised intensively on a barley/protein diet to a slaughter weight of about 450 kg.

2. Predicted basal metabolism (F′) was calculated for each trial by extrapolation to zero intake of measurements made on animals in positive energy balance. Logarithmic and linear equations are presented for F′ for bulls and steers throughout growth. Bulls had F′ values about 20% higher than steers.

3. Values for fasting metabolism (F) in young cattle are reviewed and compared with values for F′ It is concluded that observed differences within and between different estimates of F and F′ can be attributed to the impetus for growth in young animals. Thus, at a stated body weight and intake of metabolizable energy, heat production is influenced by class and breed, bulls being higher than steers and large breeds higher than small breeds.

Three groups of six young male pigs (boars) were reared from 20 days to 7 mo of age under one of the following social conditions: a mixed sex group; an all-male group; or social restriction, without physical and visual contact with other pigs. The sexual behaviour of the boars was studied from 7 to 13 mo of age. The total number of copulations and the sum of all the courting behaviour activities were significantly greater (P<0·01) for the boars reared in the all-male and the mixed sex groups than for those reared in social restriction. Growth rate to 30 weeks of age, testicle size and semen quality were not affected by rearing treatment.

1. Four experiments, each with two groups of eight pigs, were performed in a controlled environment room equipped with two pens. One pen had straw as bedding and the other had slats. The animals were exposed to temperatures of about 17°C at the initial weight (20 to 25 kg). The temperature was lowered by about 1°C per 10 kg body-weight increase, to 8 to 12°C at the end of the fattening period (80 to 100 kg).

Animals on slats were kept 4·7 to 5·3°C below the calculated zone of thermoneutrality and the animals on straw 2·0 to 2·6°C above the lower limit of thermoneutrality. In Experiments 1 and 2 the animals in both pens received the same amount of food per day and in Experiments 3 and 4 animals on slats received more food to give the same body·weight gain as on straw. Feeding level on straw was about 93 g/kg0·75 per day.

2. In Experiments 1 and 2, body-weight gain on slats was reduced due to the lower effective temperature. After adjusting for feeding level, the reduction in daily gain was calculated as 18·5 and 11·8 g per °C below thermoneutrality. In Experiments 3 and 4 the extra food needed to maintain the same rate of gain on slats as on straw was respectively 18·1 and 45·5 g per °C below thermoneutrality.

3. Carcass length of animals on slats was less than on straw.

Boars from four pure breeds and three two-breed crosses were mated at two stations to sows from six two-breed crosses to produce three- and four-breed cross litters. Two types of three-breed crosses were produced either using purebred boars or by partial backcrossing using crossbred boars. From the 504 litters produced 965 male pigs were slaughtered at 90 kg live weight. The purebred boars produced litters which were 0·4 and 0·2 pigs larger and 0·14 and 1·14 kg heavier at birth and 21 days respectively than the crossbred boars. Differences between pigs sired by purebred and crossbred boars were negligible for growth rate and carcass quality. Little difference was also found between three- and four-breed cross pigs sired by crossbred boars (except for daily gain, P < 0·05). Breed of dam was a significant source of variation on all the traits except dressing-out percentage. Significant breed of sire effect was found on all the traits related to carcass quality but not on those related to growth. Breed of sire × breed of dam interaction was significant on backfat thickness, carcass lean yield percentage and average daily gain. The best crosses in carcass value were those of Duroc boars mated to Hampshire-Landrace and Landrace-Yorkshire sows, while those pigs with the fastest gain were from Landrace boars ×Duroc-Yorkshire sows and Duroc-Yorkshire boars × Large Black-Lacombe sows.

In two experiments pigs were weaned at 2 days of age on to a liquid milk substitute, and from 7 days were either kept to 28 days in individual cages and given the liquid diet to a scale based on live weight, or kept in groups and allowed continuous access to the same diet in the form of pellets. The dry-matter intake from the pelleted diet was considerably less than that from the liquid diet, and the live weight of the pigs given the liquid diet was considerably greater at 28 days. The type of diet did not affect the feed: gain ratio. A liquid diet seems essential to realize the maximum growth potential of pigs weaned at 2 days of age. All pigs received a pelleted diet from 29 days and their overall performance from 2 to 56 days was similar regardless of initial treatment.

In a further experiment, the performance of pigs given the liquid diet was better when individually caged rather than when kept in groups.

Weaned single-suckled calves (male castrates) were offered a finishing diet which included 2·3 kg/day bruised barley (F) or a similar diet with the cereal supplement omitted (R) during the main winter feeding period. Some diet R steers had a subsequent grazing period and were re-housed for a second winter when the diet included a cereal supplement. The treatments caused differences in growth rate, distribution of slaughterings and grazing requirements. Diet R reduced growth rate and the steers took longer to reach slaughter, which was at a higher live weight, than on diet F at the same degree of finish. Steers on diet R produced 4·5% more carcass weight, 8·2% more lean, 4·1 % less fat and 11·2% more bone than those on diet F. They consumed more wet distillers' grains (21·1 %), swedes (25·5%) and grass silage (32·0%) from housing to slaughter but saved 80·0 % of the cereal consumed on diet F.

Young, uncastrated male cattle (initial weight 80 kg, final weight 240 kg) were used to evaluate brewers' dried grains as a protein source (17 or 36% of the concentrate mixture), in comparison with soyabean oil meal (6% of the concentrate mixture). There were no significant effects on feed intake or average daily live-weight gain. The killing-out percentages for the three treatments were 49·2; 48·6 and 46·9 respectively (P < 0·001). There was a lower fat deposition (P < 0·01) in animals receiving the higher level of brewers' dried grains, and the degree of rumen parakeratosis was less (P < 0·001) with the diets containing grains.

Live-weight gains were recorded for 459 intact male (bull) calves kept in 17 groups on three farms. The correlation coefficient between weight gained during the first 110 to 130 days of life and that gained during the subsequent period until slaughter was r = 0·53 (n = 459; P < 0·001). It is suggested that with bulls, nutritional and other factors which increase live-weight gain during the rearing period to about 4 mo of age may have a positive effect on subsequent performance to slaughter.