A theoretical investigation is reported into the effects of overlapping generations on the prediction of genetic gain from repeated within-population truncation selection for a quantitative trait. The gain resulting from the selection process produces genetic differences between the groups of breeding animals of different ages, and between the means of their progeny. These differences are not allowed for in the usual prediction formula. The correct allowances to make for the genetic effects of maternal age are derived for a simple situation. The implications of these allowances on the overall rate of genetic progress, and on the optimum age structure for maximum progress, are shown in a model pig breeding programme. The normal prediction formula underestimates the genetic gain which can be achieved if females are kept for five litters by 10 to 12%, and overestimates the disadvantages of keeping females for more than one or two litters.

Two surveys were conducted on commercial farms in England, Wales and Scotland to ascertain whether breeding contributed to variation in the number of lambs born per ewe, in lamb mortality and in the number of lambs remaining to be weaned per ewe. Each flock comprised two or more breed groups, but within flocks differences in breed were often quite small.

In one survey of 74 flocks (average size 198 ewes, comprising 175 breed groups) the lambing percentage averaged around 150% and the lamb deaths to weaning (including stillbirths) around 9%. Within flocks there were statistically significant differences in the number of lambs born and weaned per ewe attributable to the breed of lamb and of its dam and sire. Crossbreeding was associated with a higher weaning percentage. Lamb mortality differed significantly among breeds and crosses of lamb. Lambing performance varied with type of farm.

The second survey was a comparison of different crossbred types of dam, themselves the offspring of three breeds of sire and seven of ewe. Thirty flocks participated, providing 29 sets of records for 1-yearold females producing on average 120% lambs and losing through death (including stillbirths) 25 % of lambs born, and 10 sets at 2 years old, with 176 lambs per 100 ewes lambing and 11 % of the lambs born dying before 8 weeks old. Variation attributable to the crossbred type of the dam and to the breed of the dam's sire was significant for lambing and weaning percentage and the incidence of lamb mortality.

1. Thirty-six Ayrshire and 48 Friesian male calves were used in two separate experiments to examine the effect of level and method of feeding milk substitute in two different housing environments. The calves were weaned when the daily intake of air-dry, milk substitute plus concentrates per head reached 1·59 kg, provided at least 0·45 kg of this intake was from concentrates.

2. The feeding systems affected the total consumption of milk substitute (P< 0·001) and created differences in live weight at weaning. The housing environments affected the age at weaning (P< 0·001) and the intake of milk substitute (P< 0·001).

3. The extra capital cost involved in a ‘controlled environment’ type of calf house does not appear to be justifiable in terms of calf health or performance when compared with the performance of calves in a ‘climatic’ house in the north-east of Scotland.

Two experiments were conducted with 84 male British Friesian calves to estimate their nitrogen and sulphur requirements between 5 and 11 weeks of age. A basal 12 % crude protein (CP) diet was supplemented with meat meal, soya bean meal or urea to 15 or 18 % CP, and with sulphur to reduce the nitrogen to sulphur ratios of the diets to about 10 to 1.

The weight gains and feed conversion ratios of the calves given the 12% CP diets were significantly poorer than those of the calves fed on the diets containing 15 or 18% CP, irrespective of the CP supplement used. The supplementation of the urea-containing diets with sulphur caused a significant increase in feed intake and weight gain.

The digestibility of nitrogen and dry matter increased with increasing CP content of the diets and was greater for the diets supplemented with urea than for those supplemented with meat meal or soya bean meal. Sulphur additions also increased the nitrogen digestibility. The retention of nitrogen, when corrected for feed intake, was greater in the calves fed on the diets containing 18% CP than in those fed on the 15% and 12% CP diets.

The supplementation of the diets with sulphur increased the digestibility of sulphur, its excretion in urine and its retention. The concentration of urea in the blood plasma increased with increasing dietary CP content, and was higher in calves given urea.

In three successive years cows from an Aberdeen Angus cross Shorthorn herd were mated to pedigree Charolais, British Friesian and Hereford bulls. A comparison of the progeny of the three breeds of sire under controlled conditions was therefore possible using a random selection of dams for mating, and identical rearing of the calves. Results for live-weight gain of the suckled progeny were analysed and showed superiority of the Charolais breed over the other two when used in this form of beef cattle production.

For birth weights and daily live-weight gains, particularly during the grazing period, the Charolais cross progeny showed superiority over the other two. There was a consistent although not always statistically significant tendency for these differences between the breed crosses to occur in the male calves only, the females showing little difference between breeds. The data also showed highly significant relationships between gestation period and birth weight, both within and between breed crosses.

A comparison has been made between the methods for crude fibre (CF) and acid-detergent fibre (MADF) determination. In diets containing 10 to 70 % hay with or without 8 % tallow (T) or maize oil (MO), a highly significant (P < 0·001) correlation of r = 0·95 was observed between CF and MADF estimates. This high correlation confirmed a similar relationship found in silages, concentrate feeds and also hays. Similarly for rumen digesta, a correlation of r = 0·93 was found (P < 0·001). The equation for predicting CF from MADF calculated from diets and digesta data together was CF = 0·503+0·848 (+0030) MADF and the residual variation found was sufficiently small to provide useful estimates.

The fatty acid composition of backfat from Pietrain and Large White pigs was examined. Both the inner and outer layers of Pietrain backfat had higher concentrations of unsaturated fatty acids and lower concentrations of saturated fatty acids. Pietrains consequently had relatively soft fat.

A pair-feeding experiment was conducted with Large White and Pietrain pigs to determine whether these differences could be explained by the lower voluntary feed intake of Pietrains. The results showed that the Large Whites continued to accumulate relatively saturated fatty acids even at the lower level of feeding. It was concluded that the differences in the fatty acid composition of backfat reflect genetic differences in the capacity for fat deposition between the two breeds.

Measurements were made of apparent digestibility of dry matter, nitrogen and lipid, nitrogen balance, pancreatic lipase activity and carcass composition in eight non-pregnant sows during three 10-day balance trials during which the feed intake was 1·1, 0·8 and 2·6 kg/day of a diet containing 14·69% crude protein and 3·0 Meal gross energy/kg DM.

All the sows had similar breeding histories and had completed their fourth lactation. Four were in standard condition (mean body weight, 160 kg) and four in thin condition (mean body weight, 134 kg). All the animals lost weight and were in negative nitrogen balance while on the two lower levels of feed intake; the thin sows lost significantly more N than the standard animals (P < 0·05) and on the lowest level of feeding digestibility of DM by the thin sows was significantly less (P < 0·001).

In both groups there was a rapid recovery in nitrogen retention and in body weight when the food intake was increased.

Predictions of body composition have been made in 24 baconweight pigs of widely differing fatness, using feed intake and live-weight gain data.

Measurements of feed intake and live weight were made every 7 days throughout the growing period from 25 to 90 kg. After each pig was killed at about 90 kg, one carcass side was physically dissected and the whole empty body was chemically analysed. Multiple regression equations were then computed with the dependent variables being the weights of the physically dissectible and the chemical components. The independent variables were initial live weight, energy intake above maintenance, and live-weight gain.

The residual standard deviations of the regressions as a percentage of the mean weights of the dependent variables were for body lipid, 5·6%, fat-free mass, 3·3%, dissectible fat, 6·1 % and dissectible lean, 4·9 %. The predictions seem at least as good as can be achieved by more sophisticated techniques.

Analysis of the data allowed the efficiency of utilization of energy for protein and lipid deposition to be calculated, and an estimate of the energy costs of maintenance to be made.

The reproductive performance and food conversion efficiency ofyoung female pigs (gilts) destined for slaughter after weaning their first litter were investigated using four treatment groups of 19 Landrace × (Landrace × Large White) gilts. In two treatment groups gilts were mated at pubertal heat and suckled for 5 to 11 and 35 to 42 days respectively. These gilts were slaughtered following weaning. A third group of gilts were conventionally mated at third oestrus and suckled for 35 to 42 days. These animals acted as controls for reproductive performace. The fourth treatment group consisted of unmated gilts, slaughtered at 118 kg live weight, which served as controls for food conversion efficiency, growth rate and carcass measurements.

There were no significant differences in either the number or weight of piglets born in any of the treatment groups. The food conversion efficiency and growth rate of the mated gilts was significantly (P< 0·001) worse than that of the unmated gilts marketed at heavy weights. Of the mated gilts those mated at puberty and weaned at 35 to 42 days had the best overall feed conversion efficiency (4·56: 1) between the start of the experiment and weaning and required less food per piglet reared to 6 weeks of age than the gilts mated at third heat.

Fourteen Large White female pigs were mated at about 6 months of age and 90 kg live weight. Three of them gave birth to very small litters and were slaughtered a week after parturition at an average live weight of 166 kg. From the other 11 females 6-week-old litters with average an of 8-8 piglets were weaned. Twenty-four days after weaning the mothers, averaging 152 kg live weight, were slaughtered. Performance was compared with that of unmated females slaughtered at 90 or 130 kg live weight. After subtracting the amount of feed used normally for the production of weaned litters from the total feed consumption of the 14 females which farrowed, the feed intake per 1 kg live-weight gain was 3·67 kg, as compared with 3·43 kg and 4·46 kg in the groups slaughtered at 90 or 130 kg live weight, respectively. The average daily protein deposition in the 14 females together with their litters was 119·6 g, compared with 104·1 and 81·4 g in the control groups.

In two experiments involving a total of 48 individually-fed pigs on experiment from 20 to 90 kg live weight, the addition per kg of diet of 250 mg Cu, provided either by copper sulphate or by cuprous chloride, similarly and significantly improved daily gain and feed: gain ratio. Neither of the supplements had any significant effect on carcass measurements but both markedly and similarly increased the copper content of the liver at slaughter weight.

Two Poland China boars were mated with 12 Large White females and two Large White boars were used on the same number of females of similar background. In the post-weaning period a trial was conducted to compare the performance of purebred and crossbred progeny given a grower's diet on an ad libitum scale of feeding over the live-weight range 28 to 66 kg. Breed of boar did not influence litter size nor total litter weight at either birth or weaning. Poland China crosses compared with Large Whites grew more slowly to slaughter (10 %) but with equal efficiency of live-weight gain. Cross-breds had higher carcass yields (4 %), shorter (3 %) and deeper (2 %) carcasses, lower depths of mid-line and internal fat (11 %) and larger eye-muscle areas (22%). Breed of boar had little influence on joint proportions and no effect on carcass cut-out value. The eye muscles of crossbred carcasses were paler in colour and had higher transmission values but drip loss from the meat was not different.

The digestibility of a feed containing hull material prepared mechanically from Throws MS field bean (Viciafaba L) was determined in a 12-day balance trial with sheep. The pelleted feed contained 62 % hulls and 38 % of a concentrate mixture, and was given at a maintenance level. The mean digestibility coefficients of the feed were for dry matter, 66·3; organic matter, 68·2; nitrogen, 65·7; crude fibre, 59·4; and energy, 65·5%.

The coefficients for the bean hulls themselves, estimated by assuming coefficients for the concentrates, were dry matter, 59·6; organic matter, 61·0; nitrogen, 58·2; crude fibre, 60·3; and energy, 59·9%. By assuming a value of 2·515 Mcal/kg for the metabolizable energy of the concentrates, the metabolizable energy of the bean hulls was calculated to be between 2·00 and 2·10 Mcal/kg.

Digestibility coefficients for the bean hulls determined in vitro were found to agree with those determined in vivo.

1. Forty British Friesian and 33 Ayrshire male calves were reared on one of three treatments differing in frequency and method of feedingwhole milk and milk substitute.

2. The calves were introduced to their treatments on arrival. The Ayrshire calves were offered whole milk for 24 days as two feeds of up to 1·42 litres warm milk each (2W), or one feed of up to 2·84 litres warm milk (1W) daily, or cold milk ad libitum (AC). Thereafter they received milk substitute on one of the following regimes which were applied to the Friesian calves from arrival. The regimes were 454 g milk-substitute powder reconstituted at the rate of 158 g per litre warm water (approximately blood temperature) given in two feeds of 227 g per day (2W) or one feed of 454 g per day (1W), and milk-substitute powder reconstituted with cold water at the rate of 100 g per litre offered ad libitum (AC).

3. Calves on treatment AC had higher live-weight gains and consumed more whole milk, milk substitute and less concentrates than those on other treatments. These differences were significant. There were differences in drinking behaviour on treatment AC between Friesian and Ayrshire calves which may have been due to differences in age at the start of the experiment. Solid food intake was affected by both level and pattern of liquid milk consumption. The practical and financial implications of treatment AC are discussed.