1. Results of an experiment involving 48 individually-fed pigs, covering the growing period between about 40 and 208 lb. live-weight, indicated that reduction in the amount of water allowed per lb. of meal from 3 lb. to 2 lb. or 1½ lb. had no significant effects on either the performance or the carcass quality of the pigs.

2. Provision of an unrestricted supply of water, in addition to the allowance of 1½ lb. added to each lb. of meal, resulted in a significant improvement in the rate of weight gain which was caused almost entirely by an increase in daily meal consumption by these pigs.

3. Under the conditions of the experiment, the provision of water ad lib. was not accompanied by any adverse effects on carcass quality, although conditions under which it might do so are discussed.

4. The data on water consumption of the pigs indicated that the observed effects on performance of providing water ad lib. did not arise as a result of a deficiency in the total water intake of the pigs given a restricted supply. The possibility is discussed that the length of time that water was available to the animals might be of importance.

1. Some characteristics are described of 10 steer progeny of a Friesian bull which is known to have carried the factor for muscular hypertrophy.

2. On average these steers had a higher birth weight, lighter hide and liver, smaller feet and cannon bones, a lower percentage of fat and higher percentage of lean in the 10th rib joint, than the progeny of three other Friesian bulls reared at the same time and under the same conditions.

3. No one character was an adequate criterion for separating affected from normal progeny. It appears possible that the bull concerned was homozygous for the double muscling gene, and that all his progeny showed one or more symptoms of the condition.

Two groups of autumn born Sussex-Ayrshire cross cattle balanced for sex were raised from about 400 lb. live-weight to slaughter either on (A) a system based on summer grazing and winter feeding on silage, hay and limited barley or (B) on an indoor system based entirely on concentrates and hay.

Group A produced carcasses which averaged 531 lb. in 616 days with a higher muscle content than Group B whose carcasses weighed 496 lb. after 528 days. Steers grew significantly faster than heifers on both treatments. Maturation of Group A was delayed by scarcity of pasture in September.

From feed intakes, including direct estimates of feed intake on pasture, it was calculated that despite the check suffered by Group A, S.E. per lb. of gain was similar on both treatments and better for steers than heifers.

Since the cost per unit of feed was lower for Group A this group showed the higher margin over direct costs.

A genotype-environment interaction experiment was carried out on a total of 140 pigs. Three genotypes, produced by mating an inbred boar of each of the Large White, Landrace and Wessex Saddleback breeds to Large White sows, were fattened on conventional rations and on a high growth ration with 10% fat and growth promoting additives.

The high growth ration increased growth rate by 34% and improved food conversion ratio by 26% and gave a higher dressing-out percentage, but produced shorter and fatter carcasses. No significant genotype-environment interactions were found for growth rate or food conversion. A significant interaction was found for streak thickness but not for other carcass measurements.

1. Records on lamb mortality from birth to marking at approximately 6 weeks are summarised for four seasons in one Cheviot and three Scottish Blackface flocks and discussed in relation to the breed, environmental and management differences existing on the three farms of Sourhope, Roxburghshire; Lephinmore, Argyllshire and Glensaugh, Kincardineshire.

2. The mortality rates in single-born lambs from three-year-old and older ewes, following hill lambings, were 12% and 6% respectively in the Cheviot and Blackface flocks at Sourhope and 14% in the Blackface flock at Lephinmore. In the Blackface flock at Glensaugh, the mortality rate following regular pre-lambing feeding and lambing on cultivated pastures was 5%.

3. There was considerably heavier mortality in twin-born lambs, and in single-born lambs from two-year-old ewes, notably as a result of increased loss subsequent to birth.

4. Among single-born lambs, more males were lost than females, the difference being between 1% and 8% according to the farm and being largely due to a greater frequency of difficult births among males.

5. Lambs with birth weights markedly heavier or lighter than average had a higher percentage of mortality.

6. An abnormal incidence of loss from difficult birth in a Cheviot sub-flock in 1957 is described.

A trial is described in which normal rations containing oleandomycin at 12½ and 25 g. per ton of meal and without the additive were given to females and castrates which had previously received creep feed with and without oxytetracycline.

A total of 48 pigs were individually fed on the rations from 50 to 200 lb. live-weight, a restricted scale of intake based on live-weight being adopted.

Between 50 and 100 lb. live-weight rate and efficiency of gain were significantly better in pigs which had not received antibiotic in the creep feed. No other treatment had any significant effect on performance.

Oleandomycin did not influence carcass measurements or dressing percentage. Minimum depth of fat at the mid-back was significantly greater in pigs which had received oxytetracycline in the creep feed while castrates had a significantly greater depth of fat at the shoulder and mid-back compared with females.

Pigs receiving the lower level of oleandomycin had significantly lighter kidneys than the control animals. Other visceral weights were not significantly influenced by the antibiotic, but females had significantly heavier kidneys, spleen and liver weights than castrates.

1. For ten years purebred Blackface and Swaledale ewes have been kept on a small hill grazing together with first crosses and backcrosses to the Swaledale. The total flock of about 120 ewes was mated and lambed on sown pastures where ewes with twins remained from lambing until weaning. Four new rams (two of each breed) were used each year.

2. It is concluded that the Swaledales produced fewer lambs than the other ewes, but these were of greater birth weight (5 %) and cannon bone length (2 %); moreoever, they were better mothers than Blackface (4 %) when rearing singles on hill grazing but not if rearing twins on sown grass.

3. Blackface sheep showed greater weights at weaning (5%), at mating (5%), and of fleece (15%) than did pure Swaledales.

4. First cross sheep were equal to or slightly superior to the parental mean in birth weight, weaning weight and cannon-bone length. They exceeded the better parent in ewe weight, first fleece weight, and weight of weaned lambs.

5. Backcross sheep although not always statistically distinguishable from Swaledale in cannon-bone length and fleece weight or from first cross sheep in reproductive characters tend to confirm the interpretations placed on the relations between the purebred and first cross sheep.

6. Heterosis estimated as a superiority of first cross sheep over the mean of the two parental breeds varied from 0% for cannon-bone length to 9·5% for prolificacy of 4-year-old ewes.

Current rates of inbreeding due to A.I. and natural service are estimated in Pedigree Welsh Black cattle.

Since 1948, 27 sires have been used in A.I., 16 of which have a common male ancestor. Four sire-son pairs and two pairs and one trio of half-brothers have been in recent use. Two-thirds of the bulls and heifers bred by A.I. and registered in 1960 were sired by 4 bulls. Since 1954 progeny of two A.I. sires who are father and son, were preferred for registration.

Pedigree analysis of a sample of 128 bulls showed that those bred by A.I. were, on average, 2·80% inbred, compared with 2·32% for those from natural matings. In a sample of 166 heifers corresponding values were 0·82% and 1·17%.

One herd, through natural service, contributed 12% of the genes of a sample of bulls and heifers. Four other herds were outstanding for the number of males they provided. The average inbreeding of their young, registered bulls was estimated to be 7·04%.

The widespread use of the descendents of one bull, both in A.I. and natural service, led to 94 cases of inbreeding in the third and fourth ancestral generations of the pedigrees of animals in the sample.

It is concluded that the short term consequences of using a small number of bulls in A.I. measured in terms of inbreeding, are no different from those in natural service and that inbreeding depression in traits of commercial importance would be undetectable.

The variation and covariation of 12 linear body measurements within 60 pairs of monozygotic twin heifers is analysed in terms of a twin's mean size over a two-year period.

Possibly all the covariation, and two thirds, on average, of the variation can be accounted for by a single factor common to all the measurements.

Interpretation of this factor shows that a twin is a more or less proportional replicate of its identical co-twin. This proportionality, however, is somewhat distorted because of relatively greater differences in the later maturing body parts.

Finally it is shown that the predominant differences in both size and shape can simultaneously be described as twin lagging behind identical co-twin by 0±11·8 days' growth.

Observations on 160 Wiltshire lambs showed that shedding of the birth-coat occurred as a seasonal (normally May–July) phenomenon between the ages of 2 and 5 months. Denudation was usually considerable but not always complete. The average extent of denudation in 3 successive lamb crops was 89 %, 74 % and 92 %. Shedding usually spread progressively across the body according to a consistent, bilaterally symmetrical pattern.

Shedding did not appear to be influenced by the sex of the lamb, birthcoat type (hairy or smooth), or by follicle density, ratio of secondary: primary follicles, or fibre diameter. However, a number of different causes of variation in shedding behaviour were found.

1. Lambs born at different times tended to synchronise in onset of shedding so that they were more alike in the dates when they shed than in the ages at which they did so. Very early and very late-born lambs showed least effective synchronisation. Early lambs were older but still earlier than normal in commencing to shed; late lambs shed when younger than normal and in an atypical fashion. It was concluded that the age of the lamb, and an unknown environmental stimulus both interacted to influence shedding.

2. There was a positive association between rate of gain in live-weight and earliness of shedding. Differences in level of nutrition seemed associated with differences in rate of shedding between individual lambs and also with overall differences in the average rates of shedding between years.

3. Genetic variation in shedding was suggested by twins being more alike than half-sibs in some aspects of shedding, particularly when differences in level of nutrition were discounted.

4. In Wiltshire foetuses the order and pattern of development of embryonic follicles in different body areas resembled closely the sequence and pattern of subsequent birthcoat shedding. A causal connection was postulated.

In discussion it was suggested that there was a seasonally fluctuating environmental factor (possibly daylength), which was capable of reacting upon the Wiltshire lamb between the months of March and July. A hypothesis was developed to explain how such a stimulus could react upon the pelage follicles to produce the observed patterns of birthcoat shedding.

An analysis has been made of still-births and difficulties at parturition in a dairy herd in which purebreds and crossbreds of Friesian, Ayrshire and Jersey origin were kept. There were 2,049 calvings including 28 involving twins.

Purebred heifer dams produced 14·7% dead purebred calves (mostly Friesian and Jersey) and 6·4% dead crossbred calves (P < 0·05). For older dams the corresponding values were 2·4% and 3·6% (P > 0·05). Losses were smaller with crossbred dams. Crossbred heifer dams (two-breed crosses) with 6·5% dead calves exceeded older crossbreds with 1·9% dead calves. Three-breed crossbred dams gave similar results (8·2% and 1·2%). An intermediate size of cow of second or later parity was associated with the lowest mortality.

Friesian and Hereford sires, the calves by which were heavier than those by Ayrshire and Jersey sires, were associated with greater losses than were the latter but this applies to heifer dams and not to the same extent if at all, to older dams.

Of 52 parturitions described as difficult, 31 resulted in dead calves. Malpresentation accounted for 32 cases; the majority of these were ‘hindfeet first’. Friesian and Hereford bulls sired a higher proportion of the calves involved in difficult cases than Ayrshire and Jersey sires.

An experiment was carried out with mice over 24 generations to measure the response obtained to selection for litter size and litter weight at weaning on two dietary regimes designated normal and diluted. In addition, control groups bred by random mating were maintained on each diet. The stock were maintained on the diets from generation 0–3 after which time selection for the traits started and continued up to generation 17. After generation 17 for a further 6 generations, all selection stopped and half of each group was switched on to the other diet, while the remaining half continued as before.

No significant response was obtained to selection for either litter size or litter weight at weaning.

The diets provided did not bring about a differential response to selection for the traits, and the response to the dietary switch was small and temporary in its effect.

Due to strong maternal effects and low heritability, little genetic improvement was obtained by selection for litter size and litter weight at weaning in these mice.

1. Thirty-six Large White fattening pigs, eight to nine weeks old at the beginning of the trial, were used to study the effects of cubing pig rations.

2. There were three treatments, meal, cubes and cubes reground to meal.

3. Pigs fed on cubes had significantly higher growth rates (by 0·09 ± 0·03 lb. per day or 7·1%) than those fed on meal.

4. Food conversion was significantly lower, by 0·18 ± 0·05 lb. feed per pound gain, for cube-fed pigs. The saving in feed was 5·1% for the complete fattening period, this difference being statistically significant (P < 0·001).

5. No significant differences between treatments were recorded for any of the carcass measurements.

6. Meal-fed pigs had significantly lower dressing-out percentages than those fed cubes.

7. There were no significant differences in performance between pigs fed on cubes and ground cubes.

Callow (1962) examined methods of predicting the tissue content of sides of beef carcasses from the result of dissecting various joints, reaching the conclusion that no short cuts were possible and that dissection of the whole side was necessary. An empirical rule, suggested by Professor D. M. S. Watson, that one-third of the live-weight of beef animals is muscular tissue, was found to give a more precise estimate of the muscular tissue in a carcass than the weights of muscular tissue dissected from any individual joint. Such an assumption, that all animals have an equal proportion of muscular tissue per unit of live-weight, would be of no value in differentiating between lean and fat animals when slaughtered at a constant live-weight as is commonly done, for example, at the end of progeny tests.

A study has been made of the relative accuracy of twelve linear body measurements of dairy cattle. The results of several repeatability trials are presented together with estimates of observer error derived from the routine measuring of identical twins. Various aspects of precision of measurement have been analysed. The accuracy found from any one trial can rarely be used as a reliable estimate of the accuracy of measuring in any subsequent experiment.

The importance of observer error in identical twin studies has been assessed. It was found that from 10% to 70% of the total variation within pairs of uniformly treated identical twins could be due to measuring error. It was therefore concluded that in such studies, where observer error is a fairly large part of the total variation, a single routine repetition of every measurement would be advisable in long term experiments and several in the case of short term experiments with a small number of animals.

Measurements have been ranked for relative accuracy and the ranking was found to be broadly similar on several different criteria: (a) relative to the variation within pairs of uniformly treated identical twins, (b) relative to the total variation in a population of unrelated animals and (c) relative to the mean size of the body part. The choice of measurements on the basis of relative accuracy is discussed.