Means, standard deviations and phenotypic correlations among 28 performance and carcass variables are reported on 1042 barrows and gilts of two breeds selected at random from pigs tested by the Pig Industry Development Authority. In addition, multiple regressions predicting the lean content of the carcasses and some relationships between visual scores and other carcass variables are presented. The lean content of any one of four joints gave better estimates of overall leanness than the best combination of other measurements—that involving C, K and eye-muscle area.

Relationships were measured between growth constants for live weight and tissue weights in the hind limb sample joint in 60 Suffolk × Welsh lambs.

The lambs were random samples of five male and five female from the single-born progeny of each of six Suffolk rams. They were slaughtered as near to 75 lb live weight as possible and a standard cut of the hind limb, extending up to and including the muscles of the upper thigh and pelvis, was removed from the carcass for dissection.

Whilst muscles in the upper thigh, pelvis and abdomen were affected predominantly by sex, sire effects increased and progressively substituted them in passing down the limb.

Linear growth in body weight was positively associated with weight of bone and muscle in the sample joint but not with subcutaneous or intermuscu-lar fat.

1. Scottish Blackface and Tasmanian Merino one-year-old males were exposed to cold in climate chambers. The environmental temperature fell slowly from +10°C to −15°C in the first experiment when the sheep were in full fleece and from +30°C to −5°C in the second experiment when the same sheep were closely shorn. In the second experiment each sheep received two identical exposures separated by one day spent in a cool environment. Rectal temperatures and skin temperatures on the body and the extremities were recorded.

2. In experiment 1 skin temperatures on the feet and ears generally fell sharply due to vasoconstriction, especially in the Blackface sheep. The Blackface sheep showed earlier and more intense vasoconstriction than the Merinos.

3. In experiment 2 foot and ear skin temperatures fell smoothly with gradual vasoconstriction. In contrast to experiment 1, both breeds were similar in the time of onset of vasoconstriction. Foot temperatures, however, were significantly higher and vasoconstriction correspondingly later during the second exposure of experiment 2 than during the first exposure.

4. The skin temperature at which vasoconstriction occurred remained similar irrespective of breed, shearing or exposure occasion. But the ambient temperature at vasoconstriction was significantly influenced by all these variables.

5. Cold-induced vasodilatations were more frequent in experiment 1 than in experiment 2.

6. Retarded vasoconstriction among the Merinos in experiment 1 could, except for two sheep, be accounted for by their superior fleece cover. In experiment 2, the delayed foot vasoconstriction on second exposure was attributed to increased blood flow resulting from acclimatization.

Carcasses of 156 pigs (78 gilts, 78 barrows) slaughtered at 200 lb live weight, were probed by introscope at six positions in line with the last rib. Backfat was measured directly and muscle depth was obtained as the difference between total probed depth from skin to rib and backfat depth. The various measurements were used to predict eye-muscle area measured on the exposed cross-section of the longissimus dorsi cut at the level of the last rib.

Depth of muscle at 7·5 cm and depth of fat at 10 cm were the best predictive measurements for both barrows and gilts, although muscle at 4·5 cm in gilts and at 10 cm in barrows were of equivalent value to muscle at 7·5 cm. The correlation between observed and predicted values of eye-muscle area was 0·8. The accuracy of these predictions compared favourably with those of carcass lean percentage from maximum depth of backfat at shoulder, minimum depth of fat at loin and fat depth at ‘C’.

Two alfalfa varieties and four grass species were harvested for hay at several stages of maturity. Each hay was given to sheep to provide measures of voluntary consumption and digestibility. Digesta samples were obtained from the reticulo-rumen, omasum and abomasum by killing the sheep at the end of the feeding periods.

Sieving analyses of the digesta revealed that the fraction retained by a 0·25-mm sieve provided greater differentiation between experimental treatments than those retained by 0·5-, 1·0- or 2·0-mm sieves. The weight percentage of this fraction was used as a measure of the relative particle size despite its profound dependence on size, shape, density and distribution of individual particles.

The variation in relative particle size of digesta from different sheep fed on the same diet was illustrated by coefficients of variation ranging from 4 to 11%. Four replicates, however, were sufficient to detect numerous differences (P<0·05) between experimental treatments.

Omasal digesta from alfalfa hay had a greater relative particle size than those from the grass hays at comparablematuritystages. This may be attributable to an apparently more compact particle shape observed in the alfalfa digesta, assuming that in a simple physical sieving process the most compact particle passing a given opening will have the greatest mass. It was proposed that digesta particle shape may have greater specific importance than relative particle size for the rate of passage and voluntary intake of coarse roughage.

A direct relationship was observed between voluntary feed consumption and the relative particle size of omasal digesta from different grass hays at similar maturity stages. This was the reverse of that observed between different maturity stages within hay species. It was hypothesized that the former relationship was due mainly to changing mass of the individual particles passing the reticulo-omasal opening, whereas the latter relationship was caused mainly by the particle size distribution.

The relationship between the relative particle size of digesta from the reticulo-rumen and that of digesta from the omasum supports the theory that the reticulo-omasal opening is the site of major obstruction for the passage of coarse roughage through the digestive system of ruminants.

Two experiments were carried out in which a total of sixty-four Border Leicester × Scottish Blackface ewes were each individually fed on one of eight experimental diets from six weeks after service to parturition. The eight diets supplied four intakes of crude protein (156, 119, 90 and 65 g/68-kg ewe per day) and two intakes of energy (2923 and 2468 kcal ME/68-kg ewe per day). After parturition the ewes received one of two lactation treatments supplying a standard protein intake of approximately 260 g/68-kg ewe per day at ME intakes of 4700 and 4186 kcal/68-kg ewe per day.

The relationship between net body weight change (Y, kg) and ME (X1) and DCP (X2) intakes (per 68-kg ewe) was described by the equation Y = The DCP intake corresponding to maximum efficiency of energy utilization was 98 g/68-kg ewe per day. The relationship between lamb birth weight (Y, kg) and ME and DCP intake was described by the equation Y = 0·0003X1 + 0·0080 X2 + 2·8501.

Ewe live-weight loss during early lactation, lamb growth rates from birth to three weeks and ewe milk yield at three weeks tended to decrease with decreasing protein intake during pregnancy.

Energy intake and nitrogen balance studies have been conducted on 12 lambs fed ad libitum on four all-concentrate diets of equal crude-protein content in an experiment of latin square design. Each diet contained one cereal, either barley or oats and one protein supplement, either white-fish meal or soya bean meal.

Protein supplements had no influence on energy intake, but intake was significantly higher when the lambs were given barley rather than oat diets.

There were highly significant differences in the degree of utilization of digested nitrogen between diets containing fish meal and soya bean meal, and between diets containing barley and oats.

The energy: nitrogen ratio of urine was inversely related to the proportion of urinary nitrogen present as urea and directly related to the degree of utilization of digested nitrogen.

Studies of rectal temperature changes in Blackface lambs from birth to 24 hr indicated a very limited effect within an ambient temperature range of 28 to 66°F. The rectal temperature of twins at birth was lower than that of singles, but the difference disappeared by 3 hr after birth. Body weight was correlated with rectal temperature at birth only in twins. In both twins and singles there was an elevated level of rectal temperature after birth which was presumably associated with a postnatal rise in metabolic rate similar to that which occurs in other species. It is concluded from the results that heat regulation is completely developed within a short interval of birth.

Changes in body weight at intervals up to 48 hr were small, and body weight was significantly different from that at birth only at 48 hr in single lambs.

Twelve groups of five Israeli Friesian intact, individually fed, male calves, were slaughtered at different live weights. Commencing with 350 kg, the groups were slaughtered at intervals of 25 kg up to 625 kg live weight. Body and carcass composition data were obtained for each calf, and a feed conversion ratio was calculated.

Regression coefficients of age, feed conversion ratio and carcass data on empty body weight, and also the corresponding correlations, were calculated by the equations: y = b + αx for linear and y = bxα for nonlinear regressions.

Age increased at a rate very similar to that of empty body weight (α = 1·042). Increase in the amount of feed required to produce unit live weight was much slower (α = 0·045). With increasing empty body weight, dressing percentage and the percentage of kidney, channel and cod fat in the carcass increased moderately (α = 0·011 and 0·004 respectively), the percentage of the external organs decreased moderately (α = −0·010), and the percentage of bone in the carcass decreased very markedly (α = −0·277). The combined effect of these factors was to cause a marked increase in the percentage of saleable meat (α = 0·107) with increasing empty body weight.

Results indicate that it is possible to increase the marketing weight of Israeli Friesian male calves considerably without any detrimental effect on carcass composition or economy of production.

Five hundred and ten Danish Red male calves slaughtered for the production of veal at live weights of approximately 200 kg were used to estimate carcass composition.

Regression coefficients expressing the relationships between live weight and carcass components indicated that weight at 6 months of age consisted mostly of muscle development in the breast and hindquarters.

Variation in all of the more important growth and carcass attributes was very small, which suggested that selection responses would be difficult to obtain.

There was no apparent correlation between growth rate and the muscle, fat and bone components of the carcass. The best single indicator of the muscle content of the carcass was the muscle content of the pistol cut (r = 0·79), which itself involved complicated dissection procedures. The longissimus dorsi area provided relatively little information, and none of the body measurements, apart from the leg circumference, were strongly related to carcass composition.

The predictive value of many combinations of traits was examined. The best of them accounted for 90% of the variation in muscle content, but when the pistol cut was excluded, none of the multiple correlation coefficients exceeded 0·8.

The effects of exercise on food intake, growth rate and behaviour were investigated in two trials with 32 pigs. The exercise took the form of running or walking four times the length of a concrete path twice a day. Food intake and rate of gain in body weight were decreased by exercise; the thickness of back fat was not significantly affected. Exercise increased the amount of time spent resting. It is concluded that exercise does not appear to be a practical method of producing leaner carcasses.