Least squares analyses were undertaken on 1519 gestation lengths of cows mated to Beef Shorthorn, Hereford, Charolais, German Simmental or British Friesian bulls. Gestation length was influenced largely by breed of sireand byindividual sires within breeds. Approximately 100 calvings are required to give a mean value with a standard error of 0·50 day. Heritability of gestation length was estimated to be 0·24±0·05. It is recommended that Artificial Insemination organizations survey and publish the mean gestation lengths of their bulls and that dairy farmers modify, where necessary, pre-partum feeding in the light of this information.

Thirty-six male piglets weaned at 20 days of age were allocated to an initial slaughter group and to five dietary treatments with proteinlevels of 15·0, 17·2, 19·1, 21·4 and 23·2% crude protein at a common energy level of approximately 3·6 Meal digestible energy/kg. All diets were offered ad libitum and growth response was compared between 5 and 20 kg and 10 and 20 kg live weight. In both periods there were significant improvements in growth and the food conversion ratio from 15·0 to 17·2%, and 17·2 to 19·1% crude protein. Between 10 and 20 kg live weight dietary protein levels above 19·1% were associated with a depression in growth. Carcass protein increased and ether-extractable material decreased with increased dietary protein over the entire range studied. Retention of digestible nitrogen was maximized on the lower protein diets. Conversion of food into carcass lean was maximized on the two highest protein diets.

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.

Body size was estimated for 255 Greyface ewes using five linear body dimensions. On the basis of this calculated measure combined with a subjective measure of body size 50 small and 50 large ewes were selected for use in the experiment. Precise ovulation data were obtained by endoscopy and this technique allowed the ewes to be mated subsequently.

Body size did not affect the mean ovulation rate of the ewes although, at the same level of body condition, the large ewes were 25% heavier than the small ewes. The ovulation rates and the numbers of lambs born were influenced by changes in live weight and body condition. For these reasons live weight per se was not a good indicator of ovulation rate as ewe live weight was a combination of both body size and body condition. At the same live weight small ewes in improving body condition had a significantly higher ovulation rate than large ewes in reducing body condition.

The onset of the breeding season of the ewes was not affected by their body size. The mean date of onset of oestrous activity for both large and small ewes was 17 October 1972 at a latitude 55° 52′ N.

One hundred and forty-two kids of the Damascus breed of goat were used over a 10½-mo period to study the effects of early castration (at 7 days of age) on growth, feed conversion efficiency and carcass quality and late castration (at 7½ mo of age) on the presence or absence of taint in goat meat.

Intact male kids grew faster and used feed more efficiently than castrates until they were about 9 mo old (56 kg live weight). There- after intact kids exhibited strong sexual activity and as a result their growth ceased completely whereas castrates continued growing. Early castrates produced fatter carcasses than those of intact kids. Castration of male kids at the age of about 7½ mo (44 kg live weight) was not successful in this trial and the kids performed very poorly. A taint of varying intensity was present in the meat of intact goats but not in that from any of the early or late castrates.

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.

The length and diameter of the humerus, ulna, femur and tibia were studied at generations 10 and 14 in lines of mice selected for high and low body weight at 10 weeks of age.

Although some deviations from control were not significant, a general pattern of correlated responses was evident. The divergences of high and low line means for bone length and diameter were significant in the four bones, confirming the contribution of these parameters to genetically determined alterations in body weight. Maternal effects did not affect bone length and diameter and heterosis was not important in the genetic control of these parameters. Unlike bone length, bone diameter continued to diverge in response to the additional four generations of selection. There may therefore be differences in the quantitative genetic control of bone length and diameter and consequently in the control of endochondral and intramembranous ossification.

Twenty-one of 23 Finn and 23 of 28 Finn-Merino crossbred springborn males mated at about 6 mo of age during their first breeding season, whereas all of nine Merino males did not do so until the second breeding season at about 18 mo of age. The diameter of the testes of Finn and crossbred males at 6 mo of age was a higher proportion of their diameter at 18 mo than was that of the Merinos. Seasonal studies showed an earlier increase in the testis diameter of Merino males than that of the Finns or crossbred. At all seasons, the intensity of mating behaviour of Merinos was lower than that of the other breed types.

The results support the hypothesis that the reproductive activity of males is correlated with that of related females, and the use of male reproductive activity as a criterion for genetic selection for that of the female is discussed.

In two experiments with steers (initial live weight 339 kg) the effect of dried grass, barley and concentrates on the intake of ‘wilted’ and unwilted grass and whole-crop barley silage was investigated.

In both experiments there was no significant effect of silage type on silage dry-matter intake when given alone or with a supplement. In Experiment 1, supplementation significantly reduced (P<0·05) the intake of silage dry matter (DM) from unwilted and whole-crop barley silage. Total DM intake was significantly higher (P<0·05) for the ‘wilted’ silage diet than for either the unwilted or whole-crop barley silage diets. In Experiment 2, supplementation had no significant effect on total DM intake. Digestible energy intake was significantly higher (P < 0·05) from whole-crop barley silage supplemented with concentrate rather than barley or dried grass and was significantly lower (P<0·05) from unwilted silage diets (P<0·05) when dried grass rather than concentrate or barley was given. In the second experiment, ration digestibility and rate of passage of digesta results are reported.

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.

A model has been developed in which the voluntary food intake of sheep is related directly to metabolizable energy requirements unless physical or endocrine limitations intervene.

Although no ‘set point’ for body weight or body fat is incorporated in the model, mature sheep offered food ad libitum are predicted to reach eventually a plateau of body weight due to progressive depression of gut capacity by the increasing volume of abdominal fat. The final body weight is proportional to the digestibility of the diet. During pregnancy and lactation metabolic, physical and endocrine factors interact in such a way as to give predicted patterns of feed intake similar to those observed in practice with several qualities of diet.

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.

Teat diameters of 144 British Friesian cows were measured (1) at the proximal end of the teat and (2) 20 mm above the distal end before and after milking. Proximal minus distal diameter—‘teat diameter gradient’is used to describe shapes varying from cylindrical to funnel-shaped. Proximal and distal teat diameters and teat diameter gradient had higher values before milking than after milking. Teat diameter, teat diameter gradient and difference in gradient before and after milking, were positively correlated with milk yield and negatively correlated with somatic cell count.

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.

In some grazing experiments stocking rates are adjusted during the experiment. For these and other experiments in which the initial number of animals per treatment is subsequently reduced a more powerful statistical analysis than the normal analysis of variance may be possible. The methodology of the analysis is presented in this paper and applied to an example.

The generation interval may be defined as the mean age of parents of all progeny born, or as the mean age of parents of only those progeny destined to be selected as replacements. If the mean age of parents of replacements is used, selection differentials must be calculated within parental age groups. If the mean age of parents of all progeny born is used, the selection differential contains a component due to disproportionate selection of replacements from different parental age groups.

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.