(1) Observations were made on a group of dairy bulls at pasture during the summer of 1964. The grazing behaviour of the bulls was similar to that of cows except that they were more sensitive to disturbance and the herd instinct as seen in cows was absent.

(2) Dairy bulls in a group formed a restless community. Apart from dis turbances within the group, the presence of men, dogs, vehicles and bulls from other groups could disturb the group equilibrium. The signs of disturbance were bellowing, pawing and horning the ground, fighting and outbursts of sexual activity.

(3) No clearly defined order of social dominance could be detected and the bulls retained their individuality at all times.

1. Three experiments are reported, in which a total of seventy-two calves were weaned at 3 or 5 weeks of age and given concentrate mixtures containing either 19·2% or 11·9% crude protein, together with hay and water up to 12 weeks of age.

2. The performance of cross-bred calves weaned at 3 weeks of age and given concentrates ad libitum was significantly greater when the high-protein concentrate was used in Experiment 1.

3. In Experiment 2, in which Friesian heifer calves were weaned at 5 weeks and given concentrates ad libitum, the level of protein in the concentrates had no significant effect on live-weight gain from birth to 12 weeks. However, there was a tendency for the performance of calves given the concentrate containing 11·9% crude protein to be slightly inferior up to the age of 8 weeks.

4. When concentrate intake was restricted to 2 kg./day in Experiment 3, in which Friesian heifer calves were weaned at 5 weeks of age, the live-weight gain was significantly greater when the higher level of protein was given.

5. Daily increases in height at withers, heart girth and belly girth tended to be greater in all instances when the concentrate containing 19·2% crude protein was given, but significant differences between treatments occurred only in Experiment 3 for increase in heart girth and belly girth.

6. It is apparent from the results that the calf weaned at an early age needs to be given a concentrate containing more than 11·9% crude protein if maximum live-weight gain is to be achieved up to 8 weeks of age. The optimum protein content of the concentrate after this age seems to depend on the level of concentrate feeding. The relationship between energy and protein in determining production is discussed.

1. Eighty-four Friesian heifer calves were used in two experiments (Experiments 4 and 5) to study the protein requirement of the ruminant calf to 12 weeks of age. The calves were weaned at 5 weeks of age and given a concentrate containing one of several protein levels, together with hay and water.

2. In Experiment 4, the effect of changing the protein content of the concentrates at 8 weeks of age under ad libitum feeding conditions was studied. A concentrate containing 20·6% crude protein (air-dry basis) tended to promote more rapid weight gains in calves to 8 weeks than a similar concentrate with 12·1% crude protein. Following the change in diet at 8 weeks, both groups of calves given the low-protein diet gained weight at similar rates in the period 8–12 weeks, irrespective of the protein level to 8 weeks. During the period 8–12 weeks calves given the high-protein diet, after receiving a low-protein diet to 8 weeks, tended to gain weight at a faster rate than those given the high-protein concentrate throughout. After adjustment for differences between treatment groups in mean concentrate consumption and mean live-weight at 8 weeks, the live-weight gain from 8 to 12 weeks was significantly greater in calves given the high-protein diet after 8 weeks.

3. In Experiment 5, a significantly lower growth rate was obtained when concentrate intake was restricted to a maximum of 2 kg./day than when given ad libitum. Calves given the concentrates containing 15·9% or 20·6% crude protein gained weight significantly faster than those given the concentrate containing 12·1% crude protein, at both levels of feeding, after live-weight gain was adjusted for differences between treatment groups in mean food consumption and live-weight at 1 week.

4. It is concluded that no advantage is obtained by giving a concentrate containing more than 15·9% protein to Friesian heifer calves weaned at 5 weeks of age. The results indicate clearly the importance of an adequate supply of energy in the diet of the ruminant calf if maximum live-weight gain is to be achieved.

Phenotypic variances within pairs of monozygotic and dizygotic twin heifers and also genetic variances and heritabilities were calculated for 12 linear body measurements at a sequence of eight ages up to two years old. The 60 pairs of fraternal and 60 pairs of identical twins used were reared as part of a larger uniformity trial in which feeding was effectively ad libitum throughout.

Size differences between members of DZ twin pairs were found to be approximately normally distributed with about the same variance for all breeds and crosses. The variance within DZ pairs increased strongly with age, with a marked increase between 9 and 12 months of age and with most body measurements showing a broadly similar trend. On a logarithmic scale DZ variances increased roughly linearly with degree of maturity and at about the same rate in each body measurement. Coefficients of variation within DZ pairs corrected for measuring error had an average value of 2%. They did not change greatly with age, and were roughly the same for most body measurements although width measurements tended to be more variable than average.

Coefficients of variation within MZ pairs had a corresponding overall average of 1·4%; they declined rapidly with age from 2·0% to 1·1%, were roughly the same for all body measurements, but at early ages tended to be greater in late than in early maturing body parts. However, they showed no association with the earliness of maturing of a body part provided variation was measured at the same degree of maturity for each body part.

Genetic variation increased rapidly with age in all body measurements. The rate of increase with age was greater for late than for early maturing parts. The rate of increase with degree of maturity, however, was about the same for all body measurements. Coefficients of genetic variation increased slowly with age; they had an average value of 1·6%.

Estimates of heritability are given at a sequence of eight ages for each of 12 body measurements. They increased strongly with age from 0·14 on average at three months of age to 0·67 on average at two years of age. At any fixed age, early maturing body parts tended to have higher heritabilities than later maturing body parts. However, if heritability was measured at the same degree of maturity in each body part, early and late maturing parts had about equal heritabilities.

The present results are compared with those obtained from twin cattle studies in New Zealand, Sweden and Wisconsin, U.S.A.

Inferences from twins about genetic variances and heritabilities for unrelated animals are discussed.

The growth and carcass characteristics of semi-intensively reared Charolais × Ayrshire and Beef Shorthorn × Ayrshire cattle were studied. Charolais × Ayrshires grew faster while grazing, achieved slaughter condition at a higher live-weight and age and had leaner carcasses than Beef Shorthorn × Ayrshires. The practical significance of these results is discussed.

From the published data summarised in Table 1, it was calculated that, at an average degree of feed restriction of 15·8 %, daily weight gain decreased by 12·50% (or 0·78% for each 1% restriction), feed conversion efficiency improved by 3·96% (or 0·31% for each 1% restriction) and backfat thickness diminished by 7·63% (or 0·53% for each 1% restriction).

Equations were calculated to show the degree to which daily weight gain, feed conversion efficiency and backfat thickness change with increasing feed restriction (Figures 1, 2 and 3).

As the degree of feed restriction increases, the decrease in daily weight gain becomes relatively greater and the decrease in backfat thickness relatively smaller. Efficiency of feed utilisation, however, improves at first, but eventually decreases as restriction becomes more severe.

It is thought that the equations found can be used, within certain limits, to calculate the average effects of feed restriction for different breeds of pigs, which when fed ad libitum consume 2·7 kg. meal ration (of normal composition) per day and have a growth rate of about 750 g. daily from 30 to 90 kg., and backfat thickness of about 37 mm. when kept under average environmental conditions.

Data on 2,055 Welsh Mountain lambs showing wide variation in birthcoat type were used to study the association of birthcoat type with lamb survival and subsequent performance. Each lamb was assigned to one of six grades on the basis of its distribution of halo hair.

Lamb mortality up to weaning was associated with birthcoat type though the effect was significant only in the deaths of live-born lambs before 14 days of age. During this period fine birthcoated lambs showed the highest losses with a mortality rate of 13% compared with rates up to 5% for intermediate and hairy birthcoat lambs. The lowest overall mortality rates occurred among lambs with intermediate birthcoats.

Growth of 669 surviving ewe lambs did not show any significant correlation with birthcoat grade at any stage up to 18 months of age. However, the carcass weights and dressing-out percentages of 570 wether lambs were significantly higher among fine birthcoat lambs.

Fine birthcoats were also associated with better quality fleece grades, 86% giving rise to kemp-free fleeces with short fine fibres, while 92% of hairy birthcoats gave rise to kempy fleeces with coarser fibres.

Non-genetic sources of variation in pre-weaning death losses due to enteritis or pneumonia have been investigated using records of 15,329 rabbits born during the years 1946–61 in the random bred colony at the U.S. Rabbit Experiment Station at Fontana, California. Under consideration were periods of years, season within years, litter size, parity of doe, and fostering.

For enteritis there was a statistically significant effect of season due to a negative regression of death rate on ambient temperature. For pneumonia, periods of years were statistically significant due to an increase in later years in deaths during the first 14 days of life. The other sources of variation studied were of negligible importance.

Heritability estimates of death from enteritis or pneumonia, the two major causes of pre-weaning death at the U.S. Rabbit Experiment Station, Fontana, California, have been estimated. The data consisted of 15,329 observations made at the station from 1946 to 1961.

From birth to 14 days of age the death rate over the years increased from 0·2 to 6·1% During the period from 15 days to 56 days of age (weaning) the enteritis death rate was quite constant over the years (7·5%) while that of enteritis or pneumonia increased from 8·3% to 13·2%.

Heritability of death from enteritis or pneumonia for the period 15 to 56 days of age was estimated on the basis of paternal half sib analysis to be 0·12 ± 0·02. Based on an analysis of differences between dams within sires the corresponding estimate was 0·58 ± 0·05. The difference between the two estimates was attributed to maternal and non-additive genetic effects.

The genetic correlation between the two diseases under discussion was estimated to be 0·66 and 0middot;57 on the basis of differences among sires and among dams within sires respectively.

Breeding plans are suggested on the basis of the parameters estimated.

Comparisons of performance for growth rate were made on 15 Suffolk rams and their 362 Suffolk × Welsh progeny from 2 to 16 weeks of age or to 100 lb. live-weight, whichever was earliest.

The Suffolk rams were reared artificially from 7 days of age.

A high negative correlation was found between growth rate and efficiency of food conversion.

The correlation between the sires' growth rate and the growth rate of their progeny was 0·25. This was increased to 0·46 by limiting the performance test of progeny to the period between 8 to 16 weeks of age.

Heritability estimates increased as animals grew older. An estimate of 0·52 ±0·012 was obtained for the period 8–16 weeks of age.

1. An experiment to investigate the effect of dietary energy concentration on the voluntary intake and growth of pigs from 27·2 to 118·0 kg. (60 to 260 lb.) live-weight is described and the results discussed.

2. From 27·2 to 50·0 kg. live-weight energy intake was substantially restricted and growth retarded by diets of low energy concentration but from 50·0 to 118·0 kg. there was little difference between diets in either energy intake or growth because daily food intake of the low energy diets was increased.

3. Effects of diet on carcass quality as measured by full dissection were small except that killing-out percentage was lower on one of the low energy diets.

4. It is concluded that limited differences in the energy concentration and palatability of ingredients are unimportant in formulating pelleted diets for self-fed pigs.

Data were collected during 1961–2 on the live-weight, age and warm carcass weights of 83 lots of Israel-Friesian bull calves, 525 animals in all, the offspring of 26 sires. For varying numbers of these animals weight of various non-saleable fat components, including ruminal fat, kidney fat, inguinal fat and scapular fat were also obtained. Ruminal fat alone and ruminal fat plus kidney fat were found to be highly correlated with total non-saleable fat (r = 0·84 and 0·94, respectively). Heritability of dressing percentage was 0·20, of live-weight rate-of-gain 0·92, and of carcass rate-ofgain 0·49. The genetic correlation between live-weight and carcass weight was 0·7. Between-lot correlations indicated that increased rate-of-gain achieved through management will be accompanied by decreased dressing percentage and increased non-saleable fat content.

The data relating to twenty single location trials, involving the progeny of seven sires from one variety mated with random females from another, have been analysed to obtain estimates of sire × location (genotype–environment) interaction for egg production, 23- and 64-week body weights and 32-and 45-week egg weights. In no case was a significant interaction found, indicating genetic correlations not significantly different from unity.

The between- and within-sire components of variance have been calculated for each trait on each location separately. The regressions of these components on the mean levels at the locations have been obtained. Though low and non-significant, they tend to support the use of those locations giving maximum expression of a trait for comparisons involving that trait.

Many traits in farm animals, such as litter size or fleece weight, are the product or ratio of two or more component items. This note seeks to determine the circumstances in which selection directed at the component items is more effective in improvement than selection for the composite trait itself.

A change of one per cent in a product trait can be achieved by a change of one per cent in any of its components. The response expected on selection for a product trait or a component is proportional to h2C per cent, where h2 is the heritability and C is the coefficient of variation. Thus selection for a component trait (A) may possibly be more efficient than direct selection for the product trait (X) when is greater than . However, the correlated changes in other component traits would also have to be taken into account.

Forage crops of the genus Brassica are known to contain goitrogens which under certain conditions can cause severe incidences of neonatal mortality in lambs and goitre in older sheep (Shand, 1952; Sinclair and Andrews, 1958, 1959, 1961; Andrews and Sinclair, 1962).

In the course of studies of certain aspects of lamb growth it was noted that lambs grazing rape (Brassica napus) had heavier thyroid glands than comparable lambs grazing grass. Pipes, Premachandra and Turner (1958) found that a degree of hypothyroidism increased the rate of fattening and influenced the carcass quality of cattle, and in view of this and other evidence it was decided to test the hypothesis that changes in the weight of the thyroid glands of lambs grazing rape were associated with changes in the rate of live-weight gain.