1. Over the weight range 23–50 kg live weight, pigs were fed either ad libitum or to a restricted scale. From 59 to 91 kg live weight, eight pairs of barrows and eight pairs of gilts were fed on each of two diets varying in nutrient density. The effects of feed restriction, nutrient density of the diet and sex on voluntary feed intake, performance and carcass characteristics were studied.

2. Pigs which had been restricted grew more slowly and contained less fat and more lean at 50 kg live weight.

3. When restricted pigs were offered feed ad libitum from 59 to 91 kg live weight they ate more and had higher daily intakes of digestible energy than pigs liberally fed in early life.

4. There was evidence of compensatory growth in pigs which had received the restricted diet, but there was no significant difference in feed utilization between restricted and ad libitum pigs. It was concluded that the compensatory growth was largely the result of increased appetite.

5. Pigs finally fed on a low energy diet, in comparison with those on a high energy diet, ate more feed but less digestible energy indicating that appetite was physically limited. Efficiency of conversion of digestible energy to live weight was similar on both treatments. A higher proportion of acetic acid was produced in the caecum of pigs fed the low energy diet. Pigs receiving the low energy diet had lower killing-out percentages not entirely caused by differences in the weight of the gut and its contents. The carcasses of pigs on the low energy diet were leaner than those on the high energy diet.

6. Barrows consumed more digestible energy per day than gilts, required more feed and digestible energy per unit live-weight gain, had lower killing-out percentages, shorter carcasses, larger backfat measurements and smaller eye-muscle areas as estimated by A × B measurements. Barrow carcasses contained less dissected lean and more fat than gilts' carcasses.

7. The results are discussed in relation to other work and it is concluded that voluntary feed intake is influenced by the nutrient density of the diet and the level of energy requirement of the pig, which may be affected by previous nutritional history.

A sib selection programme for length of carcass was carried out for five generations within a closed herd of Large White pigs. A generation interval of one year was obtained.

Litter production was good throughout the project and the numbers of pigs born and reared in the final generation were 11·2 and 10·3 respectively.

Overall response to selection was predicted with reasonable success. The increase in length was associated with an increase in number of vertebrae.

Heritability for length of carcass computed from the pooled components of variance was 0·53 ± 0·12. Realized heritability was 0·5 ± 0·1. No control strain was maintained.

Correlated traits moved in the expected directions and responses were beneficial for traits such as backfat measurements and chest depth, but unfavourable for belly thickness and ham conformation. Carcass acceptability was not good initially and this deteriorated during the project. The difficulties involved in maintaining selection pressure and herd size are discussed. Abnormalities and lameness were recorded and did not increase systematically over the experiment.

It is suggested that the specific relationships between ‘conformation’, carcass value and viability require further investigation with particular reference to length of leg and length of carcass.

1. The voluntary dry-matter and water intakes of indigenous and exotic cattle on high plane rations have been compared under similar conditions of management.

2. At similar live weights, exotic cattle have a much higher feed intake relative to maintenance than indigenous cattle.

3. Water intake was closely related to dry-matter intake, irrespective of live weight, and varied only very slightly between the two types of cattle.

4. Exotic cattle were more than twice as efficient as indigenous cattle in converting feed into live-weight gain. It is suggested that this is largely a reflection of the increased feed intake, relative to maintenance requirements.

5. Stage of maturity, degree of fatness and their relation to conversion efficiency are discussed.

1. Four growth trials were carried out with 297 group-fed steers given diets based on barley, minerals and vitamins, unsupplemented or supplemented with either soya bean meal or various sources of non-protein nitrogen.

2. Steers given unsupplemented barley (11% crude protein in dry matter) had inferior growth rates up to 300 kg live weight but thereafter were equal to those given barley supplemented with urea in the drinking water or soya bean meal.

3. There were no significant differences in the growth rates of steers given barley supplemented with soya bean meal and those given barley supplemented with ammonium and mineral salts of formic acid or a mixture of acids (predominantly acetic).

4. In two out of three trials, tenth-rib joints from steers given barley supplemented with ammonium salts of mixed acids contained less fat and more protein and water than those from steers given barley supplemented with soya bean meal or proprietary protein supplements.

5. A number of possible explanations for the apparent carcass differences is discussed.

Twenty-two Ayrshire twin female cattle were kept for up to seven years of age on six equally spaced levels of constant food intake, ranging from 35 to 140 lb per week of a complete pelleted diet. Analysis was confined to the period between 5 and 7 years when growth had practically ceased and equilibrium maintenance requirements could be determined.

Equilibrium weight maintained was directly proportional to the level of constant food intake.

This relationship obtained by controlling food intake was significantly different from the 0·73 power relationship that applies across species. In establishing the present relationship, systematic genetic differences were excluded, and this is probably the main condition required for weight eventually maintained to be proportional to food intake. In contrast, the well-established proportionality of food intake to metabolic weight is essentially based on a species comparison and is thus due almost entirely to genetic differences.

A mathematical model is given which combines (1) the genetic relationship of proportionality of voluntary food intake to mature metabolic weight and (2) the nutritional relationship of proportionality of equilibrium weight maintained to level of constant food intake. The model is then used to partition variation into systematic and random components.

The experiment provides some indication of the extent of individual variation in efficiency of maintenance within breeds, the amount which is genetic, and the repeatability of this efficiency from age to age. Some information is also provided on variation in voluntary food intake, mature weight maintained and efficiency of maintenance on ad libitum feeding.

Methods of estimating efficiency of maintenance using ‘feed and weigh’ techniques, selection for efficiency of maintenance, the correlated response in mature weight, and selection for relative food capacity are briefly discussed.

1. A comparison lasting 3 years has been made of 5 types of crossbred ewes produced by mating Border Leicester, Clun Forest, Dorset Horn, Finnish Landrace and Tasmanian Merino rams to Scottish Blackface ewes. Data from a total of 576 ewe years became available.

2. In body weight at mating time when they were 7, 19 or 31 months old, the Border Leicester and Dorset Horn crossbred ewes were heaviest, followed by Cluns. Finnish and Merino crossbreds were about 15–20% lighter than the Border Leicester crossbreds.

3. In fleece weight, Finnish crossbreds were lower by about 1·0—1·5 lb relative to Border Leicester crossbreds.

4. In fertility, Finnish crossbreds were highest with 1·5, 2·0 and 2·3 lambs born per ewe lambing at ages 1, 2 and 3 years respectively. The corresponding averages for the combined Border Leicester, Clun and Dorset Horn crossbreds were 1·1, 1·6 and 1·6 and for Merino crossbreds 1·0, 1·1 and 1·2. Numbers weaned were similarly ranked.

5. Lambs out of crossbred ewes showed a sequence of group differences in weight at birth and at weaning corresponding to those shown by their mothers at mating time. The heaviest lambs were produced by Dorset Horn and Border Leicester crossbreds, and the lightest by Merino crossbreds. As a percentage of ewe weight at mating, lamb weight at weaning was highest for the Finnish group.

6. In terms of litter weight at weaning, fitted values for the Merino group were the lowest while those for the Finnish group were the highest. The other three groups gave similar and intermediate values.

1. Five hundred and fifty-two pigs were used in an experiment having six treatments. High and low protein rations were given (a) unsupplemented, (b) supplemented with 0·1% copper sulphate (CuSO4·5H2O) and (c) supplemented with 0·1% copper sulphate and 0·025% zinc carbonate (ZnCO3).

2. Performance was significantly reduced and 18 pigs died from copper toxicosis, when the low protein ration supplemented with copper sulphate was fed.

3. There were no indications of toxicity and performance was equal to the controls when the low protein diet supplemented with copper and zinc was fed.

4. The addition of copper to the high protein diet slightly reduced performance and six pigs died from copper toxicosis.

5. The addition of copper and zinc to the high protein diet improved growth rate and eliminated the toxicity associated with copper supplementation.

6. No significant treatment effects on haemoglobin or packed cell volume were observed, other than a small effect of protein level on PCV.

7. Copper supplementation of the diets significantly increased liver and kidney copper levels and liver zinc levels. It reduced liver and kidney iron contents. The addition of copper and zinc to the diet reduced the increase in liver copper associated with copper supplementation, and increased the level of zinc in both livers and kidneys.

1. Four treatments were employed in the rearing of colostrum-deprived piglets from birth to 14 days of age. The performance of the artificially reared piglets was compared with that of conventionally raised sow-suckled piglets.

2. Statistically significant differences in growth rate were found in favour of piglets receiving 22% cows' milk solids from birth when compared with the sow-suckled group and the other artificial treatments.

3. Small non-significant differences in feed conversion efficiency were found between the artificial treatments with one exception. Pigs receiving 22% cows' milk solids from birth possessed superior conversion figures when compared with pigs receiving 6% cows' milk solids after birth.

4. Each of the artificial treatments led to fewer deaths than the sow-suckled group.

5. Pigs on the artificial treatments did not undergo such rapid changes of serum protein profile as did the sow-suckled piglets. Serum protein values for the pigs on the artificial treatments rose from approximately 33% of the levels in the sow-suckled group at two days of age to approximately 60% at 14 days of age.

The relationships among five traits in dairy cattle (milk yield, fat yield, protein, fat % and protein %) were examined on the original and on a logarithmic scale. The data comprised the records on 5333 Red Danish cows tested at the Danish Progeny Testing Stations during the years 1960–66. None of the heritabilities or the correlations among the variates were altered appreciably by transformation. For the five traits heritability estimates were 0·56, 0·80, 0·65, 0·64 and 0·56, respectively. Phenotypic and genetic correlations among milk yield, fat yield and protein yield were all very high, about 0·95. The correlations between fat % and protein % were about 0·6. The coefficient of variation of a variate proved to be a good approximation of the standard deviation of the transformed variate even for milk, fat and protein yield with coefficients of variation of 17–18%. It was concluded that little is likely to be gained by using index selection for fat yield and protein yield. However, about 90% of the response obtainable by direct selection for fat or protein yield could be obtained merely by selection for milk yield. A large correlated response for protein yield could be obtained by selecting for fat yield.

1. Experiments were carried out during two winters on the effects of exposure, partial outdoor shelter and complete indoor shelter on individually penned pregnant Welsh Mountain ewes at an altitude of approximately 275 m. A single pelleted diet was given at several levels of intake.

2. In Experiment 1 ewes fed at an approximately maintenance level indoors had post partum live weights 0·9 and 1·4 kg greater than those fed at the same level in the partially sheltered and exposed pens.

3. The daily voluntary feed intake of ewes fed to appetite was 20% greater in the exposed and partially sheltered pens than in the indoor pens. But there were no consequent differences between post partum live weights, which were all higher than for ewes kept at maintenance intake.

4. In Experiment 2, when the weather was milder, the effects of exposure and shelter on ewes fed at the maintenance level were smaller and not statistically significant. Raising intake by 5 or 10% caused only small and not statistically significant increases in post partum weight.

5. Neither changes in food intake nor in environment affected lamb birth weights.

6. Ewes fed to appetite had a significantly greater wool production than those at the maintenance level. Environment had no effect on the weight of clean wool produced but penning indoors increased the weight of suint.

An account is given of the conception rates (in terms of calves born) following artificial insemination of contemporary purebred and crossbred cattle derived from purebred Friesian, Ayrshire and Jersey stock in an experimental herd. First inseminations were given to 222 purebred and 495 crossbred females approaching first pregnancy; and to 165 purebred and 347 crossbred females approaching second pregnancy. Fitted values for conception rates showed no noteworthy differences for year, season, age of female, or breed of bull. Crossbred females, however, were about 10% more likely to conceive than purebreds. Purebred females mated to bulls of their own breed showed lower conception rates than those mated to bulls of another breed.

A solution of ammonium salts of a mixture of short-chain fatty acids (mainly acetic acid) was added to the sole source of drinking water of 10 lactating Jersey cows. There was considerable variation in the concentration of salts tolerated without depression in water intake. Some animals refused solution offered at a concentration of 0·5% (w/w) whereas one animal accepted solution at a concentration of 8% (w/w) and had a mean daily intake of salts equivalent to 836 g acetic acid.

2. Adjustment of the pH of the drinking solution to 6·5–7·5 increased the tolerance to the salts solution of animals which showed a low tolerance to the unadjusted solution. A mean daily intake equivalent to 480 g acetic acid was achieved without a significant depression of water intake. Replacement of 50 % of the ammonium ions by calcium increased the intake of salts by some cows but two out of eight refused the solution at a concentration of 0·5% (w/w).

3. The addition of saccharine, vanilla or aniseed to a solution of the ammonium salts gave little or no improvement in acetate intake but sodium cyclamate, ethyl acetate or molasses reduced the variability between animals in their tolerance to the solution and increased the mean intake of salts. With an addition of molasses, which gave the most marked response, there was a mean daily intake of salts equivalent to 495±26 g acetic acid.

Profitable beef production in stickler herds depends upon each cow within the herd producing a heavy, well-grown calf every year. The weight of the weaned calf has a large effect on the producer's income. The pedigree beef breeder therefore needs to select female lines within his herd which produce calves above the herd average weight at weaning.

In parts of the United Kingdom, considerable numbers of Ayrshire bull calves are slaughtered at birth or shortly after. These animals, if fattened intensively on a cereal diet, could provide a valuable addition to the beef produced from the dairy herd if their rate of live-weight gain, carcass composition and feed conversion efficiency provided an economic return. At the prevailing purchase price of calves and cost of feed the profit margin would appear to compare favourably with that from other dairy steers. The data from an economic survey of barley beef units in the North of Scotland by Clark (1966) show, on the basis of surplus per head (i.e. gross margin less other costs) that the greatest margin was achieved by a unit whose livestock was entirely comprised of Ayrshire steers.

In reporting on the Charolais importation of 1962, Edwards et al. (1966) noted different average growth rates of calves born at different times of the year: spring born calves for instance were slowest at 1·67 lb/day and autumn born calves fastest at 1–80 lb/day. The Beef Recording Association (1967) has also reported that growth rates for castrated males in commercial intensive cereal feeding beef lots consistently reflected seasonal effects on growth. In both cases the data were derived under conditions which did not permit detailed investigation of seasonal changes in the growth curve.