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.

The intakes of concentrates and hay by individuals in three groups of ewes were estimated at three-weekly intervals in late pregnancy from faecal output; chromic oxide was incorporated as a marker in the concentrates. The groups were: (1) 16 mature ewes, (2) 16 2-year-old ewes, (3) eight mature and eight 2-year-old ewes. A constant daily hay allowance of 734 g dry matter (DM)/sheep was given but the concentrate was increased from an equivalent of 96 g DM/sheep at the beginning of the experiment to 435 g at the end. Individual concentrate intakes were most variable when the group allowance was small (CV over 50% in the mixed group) but variation decreased when amounts of concentrates were increased to contribute up to 47% of the total digestible DM intake. The CV for the total digestible DM intake ranged from 13 to 24%.

The younger sheep were at no disadvantage when penned with mature ewes. Intakes by individual ewes were compared with their calculated requirements and several twin-bearing ewes were shown to have a substantial energy deficit which was confirmed by their higher plasma ketone concentrations.

A major practical difficulty in group-feeding pregnant ewes is to ensure that the ewes with the highest foetal burden are adequately fed.

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.

Twenty-four gilts were used at each of two centres in an experiment designed to examine the effects of dietary energy intake during lactation on yield and composition of sows' milk and the growth of their litters. Gestation feed intake was standardized at 2 kg per day supplying 6·28 Meal digestible energy (DE) and 280 g crude protein. The energy levels fed during lactation ranged from 12·2 to 18·25 Meal DE per day for gilts, 12·9 to 19·6 Meal DE per day for second parity and from 13·2 to 20·25 Meal DE per day for third parity sows. Daily crude protein intake and amino acid balance ofthe protein were kept constant.

In the first lactation milk yield and composition and growth of litters were not influenced by dietary energy intake. In the second lactation milk yield was depressed by lower energy intakes and this was reflected in litter weights at 21 though not at 42 days. In the third lactation lower energy intakes seriously depressed milk yield and daily output of milk nutrients. On the lowest level of energy, milk yield was 32% lower at day 24 and 20% lower at day 41 of lactation than on the highest energy level. The corresponding depressions in litter weights were 17·2 and 13·5% at 21 and 42 days respectively.

Twenty-seven groups of Finnish Landrace × Dorset Horn lambs, each of two males and two females, were offered daily quantities of 180, 248 or 343 g milk substitute dry matter (DM) for 21, 29 or 40 days. The environmental temperature was 18°C during the first 21 days of rearing, and concentrate pellets and clean water were always available. From 22 to 48 days of age the lambs were offered 150 g of hay per week.

For lambs offered 180 g milk substitute DM, increasing the number of days before weaning increased the daily live-weight gain over the 47-day experimental period. For daily allowances of 248 and 343 g of milk substitute, greater gains were effected only by delaying weaning from 21 to 29 days.

Increasing the daily allowance of milk substitute DM had little effect on the daily gain of lambs weaned after 21 days but increased gain by lambs weaned at 29 days. For lambs weaned after 40 days growth rate was increased only by the first increment of milk substitute DM. Intake of solid food began when the lambs were 3 weeks old and total intake of concentrates was inversely related to total quantity of milk substitute DM consumed and in general was less when weaning was later.

The overall efficiency of conversion of total DM consumed to live weight was positively related to total milk substitute DM consumed and tended to be greatest when weaning was later. A daily allowance of 180 g milk substitute DM for 21 days gave the lowest food cost per unit of live-weight gain.

The incidence of navel sucking is discussed.

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 feeding value of three forms of acid-treated moist barley, viz. 26 % moisture and either rolled or plate-milled, and 29 % moisture plate-milled, was compared with that of dried hammer-milled barley for growing pigs from 23 to 87 kg live weight. Two feeding experiments were undertaken, one in which individual pigs were given the same amount of dry matter from all the diets, while in the other, groups of pigs were fed ad libitum. Digestibility of the diet was determined in a third experiment.

In both feeding experiments differences between treatments in efficiency of utilization of dry matter in the feed were significant (P<0·05), that for the diet containing dried barley being approximately 5% better than the other three. There were no significant differences between treatments in intake of dry matter, rate of growth and carcass quality of the pigs. However, pigs fed on dried barley apparently grew more rapidly than those given any of the acid-treated moist barleys. Differences in digestibility of the diets were very small and not significant except for crude protein. Differences in digestibility of protein (P<0·05), however, were not consistent with differences in efficiency of conversion of dry matter in the feed.

Gilts were allocated at 55 kg live weight to one of three treatments: 1. 1·4 kg of food daily to service, served at puberty, and 1·4 kg of food daily throughout pregnancy.

2. 1·4 kg of food daily to service, served at the third heat, and 1·4 kg of food daily during pregnancy.

3. 2·3 kg of food daily to service, served at the third heat, and 1·4 kg of food daily during pregnancy.

An attempt was made to encourage early puberty by stimulation using the presence of a boar. Natural service with boars was used on all gilts.

There were no significant differences between the treatments in time taken to reach puberty and the gilts were mated at 77, 97 and 116 kg live weight on Treatments 1, 2, and 3 respectively. The gilts on Treatment 1 had a significantly lower conception rate and a significantly smaller litter size than those on Treatments 2 and 3. However, the average birth weight did not vary significantly among treatments.

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.

The effects of selection for increased and decreased body weight in mice at 5 and at 10 weeks of age on the weight and mean fibre diameter and number of seven different muscles were studied by dissecting and histologically examining animals from large, small and unselected control lines. The purpose was to learn how selection for body size affects muscle weight and its components. Selection for increased body weight significantly increased the weight of m. biceps brachii, m. tibialis anterior, m. pectoralis major, m. brachio-radialis, m. soleus, m. rectus femoris and m. psoas major. These increases in muscle weight reflected increases in both fibre diameter and number although there were a few exceptions. Selection for low body weight produced decreases in the weight of all muscles. These reflected significant reductions in mean fibre diameter and, in most cases, fibre number. Significant estimates of heterosis in mean fibre diameter were obtained in m. biceps brachii and m. tibialis anterior from crosses between the Large and Small lines selected at 5 weeks and also between the lines selected at 10 weeks of age, respectively.

The behaviour of 12 Merino and 12 Wiltshire Horn ewes was observed on the day they werefirstintroduced together into a 0·85 ha paddock and over the following 9 days. Neither breed group had associated with sheep of the other group previously. Both groups formed and maintained their own strong social groupings, and despite the small area of pasture and enforced close association each day, no significant integration of the groups was observed.

Regression equations derived from Jersey calves fed on either chopped or ground and pelleted dried grass indicated that the volume of the organs of the abdomen or abdomen plus thorax could be predicted from simple external body measurements. The prediction equations did not differ significantly between diets. It is suggested that this measurement may be of importance in studies on the voluntary food intake of ruminants.

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.

A molassed sugar beet product with 32% crude protein and containing added urea (8%), dicalcium phosphate, trace elements and vitamins was evaluated in two experiments as a protein source for intensively-fed 100 kg British Friesian steers. Comparison was made with an equal amount of crude protein supplied as a mixture of decorticated groundnut and cottonseed meals.

Both forms of supplementation equally and significantly increased live-weight gains and improved food conversion ratios compared with those recorded when the basal diet consisted of barley with no protein supplement.

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.

1. The effects of 0·9 to 1·0 kg molassed sugar beet pulp cubes, supplemented with minerals and vitamins and with either 0, 3·0 and 7·8% urea, on the voluntary intake of oat straw (either 2·0 or 3·0% crude protein) were measured in two experiments with 250 to 300 kg British Friesian steers.

2. Straw intake was increased by a maximum of about 20% when a total of about 165 g crude protein was supplied by the urea-containing sugar beet products.

3. In one digestibility trial conducted with 385 kg steers, the inclusion in sugar beet pulp of urea equivalent to 89 g and 169 g crude protein/day comparably and significantly increased the digestibility of dry matter and crude fibre.

Complete C, N and energy balances were carried out on two mature sheep receiving a basal diet of pelleted hay plus continuous intraruminal infusions of either water or 400 kcal/day of propionic acid, butyric acid or a mixture of acetic acid and sodium acetate, for periods of 1 to 5 weeks. The efficiency of utilization for maintenance plus fattening of the basal diet and the basal diet supplemented with acetate, propionate or butyrate was 20·7 ± 1·0%, 28·3 ± 1·5%, 30·2 ± 0·5% and 31·3 ± 0·2%, respectively. The calculated efficiency of utilization for fattening (kf) of the infused energy sources was 69·9 ± 8·4%, 84·0 ± 3·4% and 86·0±2·0% for acetate, propionate and butyrate, respectively. In most instances kf did not vary with the length of the period of infusion but in one sheep there was an adverse response to the infusion of the acetate mixture, and during the first week of infusion kt was only 29·3%. During the third and fifth weeks of the infusion the corresponding values were 76±3% and 72±5%.