1. A 2×2×2 factorial experiment was carried out with 8 blocks of 8 early-weaned Friesian male calves on the 8 treatment combinations of the following factors: (A) groundnut meal versus white-fish meal as the major protein source; (B) presence versus absence of antibiotic and (C) restricted versus ad lib. feeding. The experiment was conducted over the live-weight range 55–90 kg.

2. The inclusion of fish meal rather than groundnut meal in the diet resulted in highly significant increases in both rate of gain and feed conversion efficiency (P < 0·001). This effect was most apparent at the higher level of feed intake.

3. The addition of antibiotic to the diet increased rate of gain (P < 0·001) and improved feed conversion ratio (P <0·01). Feed intake was increased slightly but non-significantly (P <0.1) on the ad lib. feeding level as a result of antibiotic supplementation.

4. Feed conversion ratio was lower and feed intake and rate of gain were higher on ad lib. than on restricted feed (P < 0·001 in each instance).

5. There was a significant (P < 0·05) level of feeding × antibiotic interaction, indicating that the difference between restricted and ad lib. feeding was greater in the presence than in the absence of antibiotic. No other significant interactions were observed.

6. The use of fish meal in preference to groundnut meal is shown to be justified on economic grounds.

Transfers were made to recipient ewes of sheep eggs stored in serum at 37° C. for up to 5 hr. (fresh eggs), in serum at room temperature for 24 to 48 hr. (stored eggs), or in Whitten's modified Krebs-Ringer-bicarbonate medium for 24 to 48 hr. (cultured eggs). The success of transfer was judged from the presence of embryos at autopsy 25–30 days after transfer.

Fifteen of 42 fresh eggs, 11 of 23 stored eggs and 3 of 15 cultured eggs were found to have developed after transfer.

The findings are discussed.

Two groups of twelve-week-old Friesian steer calves were self-fed to a slaughter weight of 400 kg. on diets composed solely of either 85% rolled barley or ground maize and 15% of a supplement providing additionalprotein, calcium, phosphorus, iron, copper, cobalt, salt and vitamin A and vitamin D.

There were no health problems on the barley diet, but five of the 15 cattle given maize died from bloat.

Surviving animals on the maize diet took 344 days to reach a carcass weight of 231 kg.; comparable data for the barley-fed cattle were 362 days and 222 kg. The tenth rib cuts from the carcasses of cattle given maize contained significantly more fat and less water and ash than comparable cuts from the barley animals. Feed conversion ratio on the barley diet was 4·76.

A comparison between the Friesian steers in the present trials and others given a lower energy diet containing ground roughage showed that with increasing concentration of the ration there was an increase in rate of gain, killing-out percentage and content of ether extract in the tenth rib cut.

Three experiments were carried out to evaluate zinc bacitracin as compared with penicillin, as a feed supplement for bacon pigs. The first experiment compared pig performance on a control diet with performance on the control diet supplemented with penicillin, 5 g./ton, or with zinc bacitracin, 10 g./ton. Experiment 2 compared the control diet with penicillin at 10 g./ton and zinc bacitracin at 10 g./ton with pigs housed in a different piggery. Experiment 3 compared the control diet with penicillin at 10 g./ton and zinc bacitracin at two levels, 10 g./ton and 5 g./ton. In none of the experiments was there any significant response to penicillin in terms of rate of gain, feed conversion efficiency or carcass composition. In the first experiment there was a small but significant improvement in rate of gain up to 100 lb. live-weight and for the whole experimental period by the pigs receiving 10 g./ton of zinc bacitracin. There was no significant response in feed conversion efficiency or carcass measurements. In the other two experiments there was no response to zinc bacitracin. The implications of the results are discussed.

Data from the Danish progeny test reports were used in an attempt to measure the genetic change in backfat thickness in the Danish Landrace breed from 1952 to 1960. Over this period the average backfat thickness of tested pigs fell from 34·2 mm. to 28·5 mm., a change of two standard deviation units.

The method used to measure genetic change depends on the differencein performance in two or more years of progeny from particular sires or dams. Environmental differences between the years are avoided by measuring performance relative to the year mean. However, allowance has to be made for selection among parents on the basis of their first set of progeny records, through adjusting the initial records by theoretical regression factors. The genetic change is then estimated as a function of the difference between the adjusted first progeny records and the records of subsequent progeny groups.

Separate estimates of the genetic change in backfat thickness were calculated in this way from the progenies of sires and of dams at each of the three stations. These were in general agreement and indicated that there was some genetic improvement in backfat thickness in the Danish Landrace from 1952 to 1960 but that not all of the observed change was genetic change. The overall estimate of the genetic change was —015±0·10 mm. per year and this represented about one-fifth of the observed change. Other less critical results are also given and these lead to the same general conclusion.

1. Sixteen foods, ranging in crude protein content from approximately 2·6 to 10·0%, were each offered ad lib. to four wether sheep. Dry-matter intake, N content and apparent digestibility of dry matter for each food were determined.

2. Voluntary intake of food dry matter was closely related to N content.

3. Slow fermentation in the reticulo-rumen and the associated slow rate of passage through the digestive tract may control the intake of low protein foods by sheep.

4. There was evidence of adaptation of sheep to low protein diets as the trials progressed and significant differences occurred in voluntary food consumption between sheep.

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.

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. 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.

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 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.

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.