A beef progeny test was organized for 66 British Friesian bulls standing at AI centres in England. Eighty-one progeny groups averaging 8-5 steers each were reared on the farms of various co-operating organizations and their growth and carcass characters were recorded. Heritability of various measurements of gain varied from 0 to 0·34, of carcass conformation measures from 0·24 to 0·50, of muscle and fat percentage in the rib joint was 0·58 and 0·46 respectively, of other measures of fatness varied from 0·04 to 0·18, of weight of feet was 0·4 and of weight of hide 0·5.

Phenotypic correlations among beef characters gave no indication that carcass composition could be predicted from the external carcass measurements or subjective scores used in this study. Genetic correlations suggested that selection for weight for age would produce a fatter and more compact carcass. Genetic correlations were high and negative between milk yield (contemporary comparison) and weight for age, carcass weight/length, and blockiness of leg, and high and positive between milk yield, and carcass depth/length and percentage bone in the rib joint. Their standard errors were also high.

1. Intake and digestibility were determined in a trial with 30 British Friesian calves given diets containing straw and either 3·2 (H), 2·9 (M) or 2·6 (L) Meal metabolizable energy per kg dry matter. For one series of diets the straw was chopped and the diets were made into cobs (1·0 × 2·5 × 4·0 cm); for a second series the straw was milled and the diets were made into pellets (1·0 × 1·25 cm)

2. Calves given the H diets containing either chopped or ground straw ate and gained less well than calves given M and L diets but there were no differences in feed intake or growth between calves given M and L diets.

3. The retention of feed residues was greater and the flow of fluid out of the rumen was less for cattle offered the H diet than the L diet.

A simple feeding system for British Friesian dairy female calves was examined. It involved once-daily feeding of a fixed amount of milk substitute to calves from 5 to 32 days of age. A comparison was made between low-fat and high-fat milk substitutes each offered at three levels of feeding. Performance was measured for a further 28 days after weaning. There was a greater incidence of nutritional scours in calves given the low-fat diets and also in those at higher levels of feeding. Live-weight gain to weaning and to 60 days was greater on the high-fat diets and at the higher levels of feeding. Intakes of concentrates, hay and water were little affected by type or level of milk-substitute feeding. Total feed costs over the 8-week period were greater for the high-fat diets and for the higher levels of feeding, but feed costs/kg live-weight gain were similar for the low-and high-fat diets. The results indicate that low levels of a high-fat milk substitute should be offered when using a once-daily feeding system in order to ensure a low incidence of nutritional scours and relatively low feed costs.

British Friesian dairy female calves were offered once daily either 320 or 480 g of milk substitute reconstituted in warm water. Weaning took place when calves were consistently eating 400, 650 or 900 g/day of concentrates. The number of days taken to reach weaning was greater with calves offered 480 g than with calves offered 320 g of milk substitute per day. Calves with a high initial live weight achieved the required concentrate intake and were therefore weaned sooner than smaller calves. A fall in energy intake occurred immediately after weaning and this was greatest in calves previously offered 480 g/day of milk substitute. The treatments had no significant effect on the total intake of concentrates and hay over the 8 weeks of the experiment. Increasing the amount of milk substitute from 320 to 480 g/day increased total feed costs, and feed costs per kg live-weight gain. Increasing the required level of concentrate intake at weaning also increased total feed costs and feed costs/kg live-weight gain, but to a lesser extent. The results suggest that it is preferable to feed dairy replacement calves only 320 g of milk substitute in a once-daily feeding system. Weaning can be successfully under-taken when the calves are consistently eating 400 g/day of concentrates.

1. Hormonexa, a bio-active feed supplement, was included at the rate of 3·1 kg per 1000 kg of the concentrate ration for finishing Hereford · Ayrshire steers.

2. Live-weight gain and food conversion were unaffected by the addition of Hormonexa.

3. The killing-out percentage of the supplemented animals was significantly lower and their carcass quality was slightly, but not significantly, lower than that of the control animals.

Forty-eight uncastrated buffalo male calves and 16 male Friesian × Egyptian Native calves were used in two experiments to study the effect of weaning age on the performance of calves fed on a high concentrate ration after the first four months of age. Half of the buffalo calves were weaned at 120 days of age on to 330 kg whole buffalo milk (late-weaned) and the other half were weaned at 45 days of age on to 100 kg whole buffalo milk (early-weaned). Cattle calves were weaned at 31 days of age on to 65 kg whole cow milk. At the age of 7 days the calves were put on a high energy ration of 74% total digestible nutrients and 13·5% digestible protein. After 125 days of age all calves were offered a high concentrate ration (cottonseed cake and rice bran in the ratio of 1:1, plus 2% Ca(OH)2 and 1% common salt). Air-dried roughage was supplied at a level of ½% of the body weight. Buffalo and f-Native calves reached a slaughter weight of 400 kg or more about 540 days of age. Three-quarters Friesian calves reached the same weight at 480 days of age. The high concentrate ration caused a high incidence of bloat in ¾Friesian bulls. The efficiency of feed utilization was better for cow calves than that for buffalo calves. The system of early weaning of buffalo calves proved to be most economical and saved about 26% of the cost per kg live-weight gain. Slaughter experiments indicated that fat deposition was greater in male cattle of 400 kg than in buffalo bulls.

Wafers of dried grass which differed in particle size (modulus of fineness) were prepared and fed ad libitum to cattle and sheep. The response of the two classes of stock to the feeds was similar. The digestibility of organic matter and of cellulose decreased with decrease in modulus of fineness (more fine particles) and this was associated with more rapid passage of the finely-milled material through the alimentary tract. Organic matter intake generally increased with decrease in modulus of fineness, but the pattern of response differed between experiments. In one experiment the difference in voluntary intake between feeds with modulus of fineness of 2·5 and 1·0 was less than 5% and not significant, but in a second experiment the intake of feed with modulus of fineness of 2·1 was 18% lower than that of feed with modulus of fineness of 1·0. In the first experiment the wafers broke down during handling and feeding with the result that the feed of low modulus of fineness was extremely dusty, but in the second experiment a binding agent was included and little breakdown of wafers occurred. It is suggested that dustiness may have restricted the intake of some of the feeds in the first experiment. Intakes of digestible organic matter did not differ significantly between treatments in either experiment.

Data on growth rate and carcasses of pedigree Polled Dorset Horn castrated male lambs have been collected. The lambs were the half-sib progeny of 18 rams mated to groups of 20 ewes in 1968 and 1969. The lambs were slaughtered at between 35 and 45 kg live weight and when considered ‘fit’ on the basis of a handling appraisal. The whole carcasses were classified by a retail organization as either ‘accepted’ or ‘rejected’ and subsequently all carcasses were cut into commercial joints ready for sale. Analyses indicated that classification of carcasses was largely but not solely based on backfat thickness. Accepted carcasses were from older and heavier lambs which had larger eye-muscle areas. There was no difference in value per unit weight between accepted and rejected carcasses.

Heritability for growth rate to 16 weeks of age was zero but for growth rate and age at slaughter was 0·26 ± 0·22 and 0·28 + μ 0·22 respectively. The heritability estimates for percentage best end, loin and backfat thickness were greater than 0·30. There were insufficient data to estimate genetic correlations accurately, but the estimates of pheno-typic correlations and heritabilities were very similar to those obtained in a previous study of carcasses of Down cross lambs.

It is suggested that the method of choosing lambs for slaughter accounts for the large difference in the heritabilities for growth to 16 weeks and to slaughter. Selection to change backfat thickness would be effective and would probably result in a reduction in age at slaughter and an increase in growth rate to slaughter. Selection to change proportions of the carcass is not considered to be worthwhile.

1. Twelve blocks of six enzootic-pneumonia-free Large White litter-mate pigs were individually fed, wet, from 20 to 92 kg live weight on six different levels of feed intake. Four groups were fed according to scales based on live weight and two were fed on a ‘semi-ad libitum’ system. One of the scales used was based on the ARC (1967) recommendations.

2. Pigs on ‘semi-ad libitum’ feeding grew significantly faster than those on scale feeding although the feed: gain ratios were similar. Differences in performance between the four scale-fed groups were relatively small.

3. Although treatment differences in carcass measurements were in the main small, the commercial grading results favoured the carcasses from the scale-fed pigs. The firmness of backfat assessed by thumb pressure was reduced as the level of feeding was increased.

4. The results were compared with those obtained in a similar trial carried out at Shinfield in 1957 using pigs of a completely different genetic background. The general conclusions reached were similar in the two trials, that to obtain the most satisfactory overall results some form of controlled scale-feeding was necessary.

1. Six pigs, four with caecal cannulae, were given diets containing 8% or 26% cellulose. Cannulation did not affect the digestibility of dry matter or cellulose.

2. Digestibility of cellulose, though variable, was higher for the 8%-cellulose diet.

3. Pigs on the 26%-cellulose diet had larger amounts of digesta in the caecum, and lower caecal retention times, than pigs on the 8%-cellulose diet.

4. Measurements of production rates of volatile fatty acids in the caecum indicated that only 2·7% and 1·9% of the apparent digestible energy of the 26%- and 8%-cellulose diets respectively came from the acids, and it was concluded that the caecum played only a small role in the breakdown of feed substances.

One hundred and twenty eight gilts by Landrace sires out of Large White × Landrace females were allocated on the basis of litter relation-ship and initial weight to 16 treatments involving the individual feeding of four dietary protein levels (approximately 15%, 18%, 21% and 24% CP) at each of four energy levels (2830, 3100, 3375 and 3585 kcal DE/kg air-dry feed). Amino acid balance (as% of total CP) was maintained relatively constant, using synthetic lysine and methionine where necessary. Growth performance was measured over a live-weight range of 23 kg to 59 kg, at which latter weight the pigs were slaughtered for carcass evaluation by dissection of the middle ‘joint’ from a half carcass. Linear carcass measure-ments were also taken. There was a significant energy × protein interaction only for killing-out percentage; for all other measures the main effects could be assessed independently. Increase in dietary energy value gave linear increase in growth rate (GR) and improve-ment in efficiency of feed conversion (EFC), accompanied by linear decrease in lean percentage and increase in fat percentage. Increase in dietary protein level gave an increase in GR and improvement in EFC with the first increment (from 15% to 18% CP), but depressions in both these characteristics with the final increment (from 21% to 24% CP). Lean percentage increased and fat percentage decreased with the first protein increment, with no further significant changes. Calculation of daily rates of tissue deposition indicated that maximum rate and efficiency of fat-free carcass gain could be attained with the second lowest energy and protein levels tested (i.e. 3106 kcal DE/kg and 18·2% CP).

Two barrows and two gilts from each of 16 litters, by Landrace sires out of Large White × Landrace females, were fed individually one of 4 dietary protein levels (approximately 14%, 17%, 20% and 23% CP) at a common energy level (approximately 3165 kcal/kg DE), from an initial weight of 23 kg to slaughter at 59 kg.

The 17% CP diet gave 19% faster growth and 17% better feed conversion than the 14% CP diet (P < 0·01) with no evident change resulting from further increase in protein level, while the 23% CP diet gave 29% more lean than the 14% CP diet (P< 0·01), as assessed by dis-section of a sample joint.

There were no significant differences between sexes in growth rate, efficiency of feed conversion or carcass composition. Only depth of backfat on the shoulder and at ‘K’ and carcass length showed significant (P < 0·05) sex differences, and the only sex × diet interaction was in eye-muscle area. The results are discussed in relation to those presented in the previous three papers of the series.

A field trial was conducted at 13 centres to investigate the effect of increasing feed intake on the day of mating on litter size of sows. From weaning to mating, control animals received 1·8, 2·3 or 2·7 kg food/day depending on the managemental procedure of the centre. Flushed animals were fed in the same way except on the day of mating when their feed allocation was doubled. Flushing did not significantly affect litter size when the overall results of all centres were considered (447 sows). Results for individual centres were also examined. A significant response to ‘flushing’ was obtained at only one of the 13 centres, where increasing feed intake from 2·7 to 5·4 kg on the day of mating significantly (P < 0·05) increased litter size by 1·3 ±0·52 pigs born.

The relative concentration of the fatty acid components of the total intramuscular lipids from six muscle locations of pigs at 1·5 to 54 months of age were assessed by gas liquid chromatography. Although the pattern was generally similar at each location, differences between locations in the concentrations of oleic and arachidonic acids in particular were noted.

Differences between animals in the relative concentration of fatty acids (other than linoleic) could not be accounted for by the pattern of dietary intake.

The macroscopically measured thickness of the skin of bacon-weight pigs has been found to differ between entire boars and castrates. The histological analysis showed that this difference can be attributed to a significantly stronger development of the dermis in the boars compared with the castrates.

A control diet was compared with a diet containing 2 mg diethylstil-boestrol (DES) plus 2 mg methyltestosterone (MT) per kg air-dry feed, the hormone treatment extending either from 20 to 84 kg live weight or from 50 to 84 kg live weight. The experiment contained 20 blocks, each of 3 littermate castrated male pigs individually penned and fed to a restricted scale. Hormone supplementation had no effect on growth performance and significantly affected car-cass characteristics only when given for the longer period. Killing-out percentage, backfat thickness and percentage subcutaneous fat plus skin in the gammon joint were reduced and carcass length, percentage bone and percentage lean in the gammon joint were increased when the supplement was given over the longer period.

Some aspects of sexual development and mating behaviour in Clun Forest ram lambs having a wide range of birth dates were studied during two seasons. The 61 ram lambs studied were introduced individually to Clun ewes in oestrus, for short periods at fortnightly intervals during late summer and autumn. Complete matings, i.e. intromission and ejaculation, were first achieved at a mean age of 6 months (range 142–223 days) and a mean body weight of 35 kg (range 24–49 kg). The attainment of physiological puberty preceded the first copulation, often by several weeks. A few individuals had abnormal testes and were partly or completely sterile, but exhibited normal mating behaviour. Early-born lambs tended to complete their first matings at a higher age and heavier body weight than late-born lambs, which suggests a possible seasonal influence on the development of breeding activity in the ram lamb.