1. Four groups of eight castrated male lambs, weighing initially about 37 kg, were fed ad libitum for 18 weeks on: C, chopped dried grass throughout; P, pelleted grass throughout; C/P (or P/C), the two forms alternated every 3 weeks; or C + P, both forms on offer.

2. Daily dry-matter intake (g/kg W0·75) was 58·2 for treatment C and 814 for treatment P; thus the long-term difference in intake was 40%. However, in the alternated sheep, dry-matter intake was 53·6 g/kg W0·75 for chopped grass and 86·5 g for pelleted; this short-term difference (61%) was significantly greater than the long-term difference. Dry-matter intake for treatment C+P was 84·9 g/kg W0·75; after the first week, chopped grass comprised only 10% of this. Dry-matter digestibility coefficients (%) were: C, 740; P, 61·4 and C+P, 62·0.

3. The sheep were killed in week 19 and the dimensions of digestive organs and their contents were adjusted to an animal of 50 kg empty body weight. The weight of the reticulo-rumen was greater for C (1·30 kg) than for P (0·94) or C+ P (1·05), C/P and P/C being inter-mediate (1·15). The water-filled volume of the rumen was proportional to weight, except that C/P (alternated sheep finishing on pelleted grass) had low volumes. Reticulo-rumen fill was greater for C (7·28 kg) than for P (3·97) or C+ P (4·53), P/C (5·90) and C/P (4·34) being intermediate. There were no other significant differences in organs or contents.

4. Gains in empty-body weight (g/day) were: C, 112; P, 181; C/P and P/C, 126; C + P, 195.

Two trials were conducted using two breeds of sheep varying in prolificacy but producing high commercial milk yields. In the first, 85 Chios ewes were assigned at 10 weeks before lambing to one of three planes of feeding: L, straw ad libitum; M, straw ad libitum + 0·5 kg concentrates; and H, straw ad libitum +1·0 kg concentrates. Six weeks prior to lambing, treatment L was stopped and all 85 ewes were re-randomized to treatments M and H. They were kept on these treatments until 14 days after lambing. In the second trial, 54 Chios and 56 Awassi ewes were allocated to the M and H treatments 6 weeks prior to lambing. After lambing they were fed ad libitum on straw and concentrates for 28 days.

The mean metabolizable energy intake (Meal/day) over the 6-week period before lambing was 2·78 and 3·96 for Chios ewes in Trial 1, 2·39 and 3·51 for Chios ewes in Trial 2 and 2·66 and 3·72 for Awassi ewes in Trial 2, for the M and H treatments respectively.

In both trials the treatment of the ewes affected the birth v/eight of twin and triplet lambs but not that of singles. In Trial 1, the differences in 14-day milk yield between treatments M and H were highly significant. In Trial 2, however, in which the ewes were fed ad libitum during lactation, no differences in the 14-day or the 28-day milk yields were observed for either breed. It is concluded that milk yields in early lactation are closely related to actual plane of nutrition in lactation but may also be affected by the body condition of the ewe at lambing, which may in turn be influenced by a low level of feeding in pregnancy.

Silage made from a whole crop of barley was offered to sheep without neutralization or after partial neutralization to pH 5·4 to 5·5 with sodium bicarbonate or ammonia. In a further treatment the un-neutralized silage was supplemented with blood meal administered each day as a drench. Total organic-matter intake and nitrogen retention were significantly higher for the sheep receiving the blood meal supplement than for any of the other treatments, which did not differ significantly one from another. It is suggested that the intake of the un-supplemented silage was limited by a low uptake of amino acids from the intestine.

Shorn Blackface sheep were acclimatized to cold by acute or chronic exposures. Acclimatization caused increased resistance to body cooling (IRC) during acute exposure and elevated heart rates at thermoneutrality (28°C). The length of time these effects were retained during subsequent periods at thermoneutrality was monitored.The effect of moderate heat stress (36°C) on previous cold acclimatization was also measured in Blackface and Merino sheep.

Conclusions were:

1. IRC resulted from previous exposure to chronic cold or acute cold. IRC induced by chronic cold began to decay after 2 weeks at thermoneutrality. IRC induced by one acute exposure was maximal 2 weeks after exposure and had disappeared by 8 weeks. IRC induced by two acute exposures combined with chronic cold showed little decrease even after 8 weeks at thermoneutrality.

2. Merino sheep showed 50% lower initial cold resistance and smaller IRC following acclimatization than equivalent Blackfaces.

3. Heat stress for 10 days after cold acclimatization had no effect on IRC in Blackfaces or Merinos.

4. Heart rates measured at 28°C were increased by 20 to 50% following acute and chronic cold exposure. After 3 days at thermoneutrality about 70% of the increase remained; but after 8 days almost all the increase had disappeared.

5. Two components of cold acclimatization were distinguished:

(i) Increased resistance to body cooling probably caused by an enhanced peak metabolic rate capability.

(ii) Increased resting metabolic rate evidenced by high heart rates. After the cessation of cold treatment the rates of decay of these two components were different.

Ninety-six lamb carcasses drawn from six batches of lambs commercially consigned to an abattoir were analysed for characteristics which may affect their economic value. From each batch carcasses were selected in equal numbers into two classes of ‘good’ or ‘poor’ conformation according to traditional standards. Carcasses selected for ‘good’ conformation were heavier (P<0·05) and fatter (P<0·05), slightly shorter in carcass length and hind leg length (P<0·05), greater in circumference (P<0·001) and width (P<0·001) of the hind leg, slightly greater in muscle weight (P<0·05) but no greater in bone weight than those of poor conformation. The yield of prime retail joints was similar in the two conformation classes but the ‘good’ conformation class had a higher proportion of loin and rib joints and lower proportion of hind leg joint (P < 0·01) although these differences were not considered to be of commercial importance. There was a lower proportion of the carcass fatty tissue in the hind leg joint of the ‘good’ conformation class (P < 0·05). Muscle-to-bone ratio and area of ‘eye muscle’ (M. longissimus thoracis) appeared to be little affected by selecting for conformation differences. Depth of fleshing as indicated by the weight of muscle in the hind leg per 10 cm length, was 40 g (6%) heavier in the carcasses of the ‘good’ conformation class. This contrasted with the much greater differences, between batches, of 290 g (40 to 50%). Between batches there were significant differences for all the measures taken except the yield of preferred retail cuts. In the main the batch differences were greater and commercially more important than the conformation class differences.

1. The experiment was designed to compare the protein and energy metabolism of pigs growing at 25°c or 34°C. The pigs were given two levels of feeding while growing between 25 and 75 kg live weight.

2. The high temperature was associated with increases in rectal temperature of 1·2 to 20°C. Both pigs on the higher level of feeding at 34°C became lame in their hind legs.

3. The high temperature was also associated with increases in heat production and in urinary nitrogen and energy losses for pigs fed at the higher level of feeding only; however fasting heat production was not affected significantly by temperature. The high temperature had no effect on the apparent digestibility of the diet.

4. It was calculated from data for pigs at both levels of feeding kept at 25°C, that efficiency of utilization of metabolizable energy (ME) above maintenance was 71%, and the maintenance requirement for ME was 100 kcal/kg0·75 day. Energy retention was reduced at 34°C in pigs fed on the higher level of feeding.

1. A total of sixty, 7-day-old British Friesian male calves, reared on a conventional early-weaning system, were used in two experiments in which dried skim milk was partially replaced by levels of 7, 14 and 21 % cooked potato flour (CPF). In the first experiment the diets were iso-energetic but differed in total nitrogen contents, whilst in the second experiment, casein was used to make the diets iso-nitrogenous.

2. In both experiments, diets containing CPF depressed growth rate from 4 to 18 days on treatment (11 to 25 days of age) and reduced the firmness of the faeces. These effects were correlated with the concentrations of CPF in the diets, live-weight gain being depressed by 20%, and the firmness of the faeces by 14%, for each 10 % inclusion of CPF. After 18 days on treatment (25 days of age) these effects became less pronounced.

3. The overall performance of calves to weaning (after 35 days on treatment) was similar on all diets. Daily live-weight gains from 4 to 56 days and 35 to 56 days did not differ between treatments. 4. It was concluded that whilst the inclusion of CPF in the diets of milk-fed calves was unlikely to have any permanent effect on the live weight of calves at 5 or 8 weeks of age its use in milk diets for calves of less than 3 weeks of age must be limited if loose faeces are to be avoided.

A simple model is described which enables the prediction of the magnitude and direction of the responses of growing pigs to different energy and protein intakes. The model calculates daily live-weight gain from the conversion of the dietary supply of crude protein and energy into protein, lipid and ash in the body of the growing pig. Values were also determined for the energy and protein balances, the composition of the body and the efficiency of feed conversion. The model was formulated with factors drawn from published findings and validated by comparison with independent feeding trials.

1. A split-plot design was used to study apparent digestibility of dry matter, gross energy and nitrogen of a whole grain wheat diet and processed (hammermilled, rolled or hammermilled and then steam-pelleted) wheat diets by eight small (33·9 ± 0·1 kg) and eight large (70±1·7 kg) pigs. Metabolizable energy and nitrogen retention were also studied with the small pigs.

2. The processed wheat diets were superior to the whole grain wheat diet in all the parameters measured.

3. There were no significant differences between the performance of pigs given the differently processed wheat diets.

4. Apparent digestibility of dietary components particularly in the whole wheat diet was significantly higher when diets were given to small pigs than when given to large pigs.

The effect of the presence of rams upon the blood LH levels of ewes just at the start of the breeding season has been studied. It was found that there was a large and sudden increase in LH levels of ewes exposed to rams when compared to a control group. There were also small but non-significant effects on the mean date of the start of the breeding season and upon the number of lambs born.

An experiment was carried out in which equal amounts of concentrate were given to beef cattle once, twice or three times per day, with a basal hay diet. There were no significant differences between treatments in food and water intake, digestibility coefficients, nitrogen balance data or live-weight gain.

Female pigs of the Pietrain and Large White breeds, 18 from each, selected to form a logarithmic weight range, were dissected into their major carcass tissues. Relative to carcass growth, fat was the fastest developing tissue in both breeds; fat and muscle grew at a rate higher, and bone at a rate lower, than the carcass. The growth of bone relative to carcass growth was faster in the Large White; differences between breeds in the growth of muscle and fat were not significant. Muscle weights and muscle: bone ratios, estimated at the same empty body weight, were greater for the Pietrain over the entire body weight range studied. There was no significant difference in muscle: bone ratio between the Large Whites used in the present study and those dissected by McMeekan over 30 years previously. The breed difference in the proportion of muscle and bone at the same body weight is attributed to a greater maturity of the Pietrain.

Six lines of mice were fed distinctive fixed or shifting diets while being selected for fast growth in the first two weeks after weaning. The intention was to provide alternative routes for the improvement of growth with respect to a maize diet (100% maize) where controls grew 6 g, an optimum diet (76% maize, 24% milk) where controls grew 17 g, and a ‘milk’ diet (16% maize, 84% milk) where controls grew 12 g. After 10 generations of selection the lines, hybrids and unselected controls were compared on these and intermediate diets. Realized genetic correlations between growth on optimal and suboptimal diets depended on the feeding regime in which selection was practised, and were significantly higher in lines that were selected on suboptimal diets. When the selected lines were tested on unfamiliar suboptimal diets they were hardly better than controls, but on their own diets and also on the optimum diet were about 6 g heavier. Peak growth was never much greater than on 76% maize and was made on diets containing between 58% and 82% maize. With one exception, the hybrids grew on each test diet about as well as did the best selected line.

A genetic limitation was encountered on the optimum diet. The growth there of the mice selected on either milk or maize diets was not improved upon by the mice actually selected on the optimum diet.

Selected sample joints from the right sides of twelve 18-month-old Friesian steers were used to compare their accuracy in predicting carcass composition. Results indicated that whilst the shin joint proved the more accurate predictor of carcass muscle and bone contents, the loin (ribs 11 to 13) or foreloin (ribs 9 to 10) proved more useful in predicting total carcass composition, provided carcass weight was included as an additional variate.

The digestibility and N contents of samples collected by oesophageally-fistulated sheep and by hand plucking were compared. Hand plucking overestimated nutritive value at high levels of digestibility and N content, and underestimated nutritive value when this was low. The differences between fistula and hand-plucked samples varied between pastures. Precision was increased when samples were combined between operators.

Half carcasses of 18 Pietrain and 18 Large White female pigs were each dissected into 93 muscle units. An allometric analysis of the weight of these units relative to total muscle revealed increasing craniocaudal and distoproximal growth gradients, which were more pronounced in the Pietrain.

The greater total weight of muscle, shown previously for the Pietrain at any given body weight over the range studied, was not due to higher muscle weights in any particular region at birth, but at 60 kg body weight was due to heavier high impetus muscles. Heart weight relative to total muscle weight was higher for the Large White over the entire range.

It is concluded that for the animals studied the changes in muscle distribution are related to the functional demands of an increase in body size, and that the muscle distribution of pigs can differ between breeds.

The appetite and growth of individually-fed, weaned Hampshire and Saddleback piglets and of Hampshire and Large White × Landrace piglets were compared in three experiments from 14 to 49, 28 to 55 and 21 to 45 days of age. There was a reduced rate of growth in the Hampshire piglets, which was not found to be related to any need of Hampshire piglets for a higher quality diet. Neither was there any reduction in the efficiency with which Hampshire piglets used ingested nutrients, nor a differential rate of deposition of any body component. Hampshire piglets ate less food than Saddleback or Large White × Landrace piglets and this reduced appetite was largely accounted for by the lower body size.

Two Pietrain/Hampshire crossbred males and two Large White males were mated in equal numbers to 24 Large White females. Breed of sire did not affect litter size or total weight at birth or weaning. After weaning, on ad libitum feeding over the live-weight range 25 to 88 kg, the crossbred pigs grew more slowly to slaughter (5%) but with equal efficiency of live-weight gain. Crossbreds had higher carcass yields (3%) shorter carcasses (3%) and larger ‘eye-muscle’ areas (18%). Fat depths, joint proportions and cut-out values were not affected. The ‘eye-muscles’ of crossbreds were paler in colour and had a lower water-binding capacity than those of the purebreds, but pH1 values and transmission percentages did not differ.

In two experiments carried out on 36 crossbred growing lambs the effect of purified bovine somatotrophic hormone (STH) on wool production and some qualitative fleece characters was studied. Food intake during and after the hormonal treatment was also examined. STH, injected in a dose of 1 mg/kg of body weight in 10- or 15-day intervals to growing lambs from 2 to 100 days of age, increased fleece weight significantly. This increase was accompanied by considerably higher daily food intake both during the hormonal treatment and 15 weeks after cessation of STH injections. No significant effect of STH on qualitative fleece characters was found.

The present study investigated the intensity of the anoestrous period in 36 Hampshire and Suffolk ewes as influenced by the photoperiod and the presence of the ram. The study began on 4 April and terminated on 11 June. Ewes kept under natural light in the absence of the ram (Group I) exhibited a limited amount of ovarian activity as determined by cervical smear. Ewes kept under natural light, but in the presence of a ram (Group II) showed an increased amount of cycling (P < 0·05) when compared to that in Group I. Two ewes from Group II mated during the so-called anoestrous period and subse-quently lambed. Ten of 12 ewes, subjected to a decreased photoperiod (Group HI), increased ovarian activity within a few days of light reduction. Five ewes in this group lambed.