1. A series of calorimetric experiments was conducted with sheep which had fleeces ranging in thickness from 0·1 cm. to 12 cm. at environmental temperatures between 8 and 32° C. Heat production, heat loss by radiation, by convection and conduction, by vaporisation of water and due to warming food and water to body temperature were measured together with losses of energy in faeces, in urine and as methane.

2. The effects of a rise in environmental temperature on digestion of the food and on the loss of energy in urine or as methane resulted in a slight rise in the metabolisable energy of the ration by 6 Cal./° C.

3. Environmental temperature had a marked effect on heat production, particularly when the fleece was short. The critical temperature (i.e. the environmental temperature at which heat production was minimal) of the closely-clipped sheep varied from 24° C. at a high level of feeding to 38°C. at a sub-maintenance level of feeding. These critical temperatures are similar to that of naked, resting man but much higher than that of the pig when fed similarly.

4. As the fleece grew the critical temperature fell. Thus, on a maintenance level of feeding, a sheep with a fleece of 0·1 cm. had a critical temperature of 32° C.; when the fleece had grown to 2·5 cm. the critical temperature was 13° C. while with a 12 cm. fleece the critical temperature was 0° C.

5. Below the critical temperature heat losses increase more rapidly in sheep with light fleeces. Thus a heavy fleece not only depresses the critical temperature but also reduces the rate of increase of heat loss with falling temperature under sub-critical conditions.

6. At environmental temperatures well below the critical, the heat losses of the sheep per unit surface were identical. Under such conditions, when the whole of the metabolisable energy of the food is used to keep the animal warm, the criterion of ration adequacy is a high content of meta-bolisable energy in small bulk.

7. At environmental temperatures above 32° C. the heat production on a constant ration increased, the rise being greatest with the highest level of feeding. Consequently the net energy value of the food declined at these high environmental temperatures.

8. The calorimetric experiments were supplemented by two comparative feeding trials in which the effects of normal outdoor environmental conditions on the body weight of groups of Cheviot and Blackface sheep were measured. Control groups were kept indoors in heated pens.

9. During the mild winter of 1956-7 the out-wintered Blackface wethers i n full fleece did not loose any more weight than those fed the same rations indoors.

10. During the more severe winter of 1957-8, Cheviot, in-lamb ewes kept on a maintenance diet gained 2·3 lb.; those kept outside on the same ration lost 3·3 lb. With Blackface, in·lamb ewes the difference between the two groups was 0·3 lb. in favour of the indoor group.

11. The food utilisation of sheep is affected considerably by environmental conditions. With little fleece the critical temperature is high and even when in full fleece an effect of cold can be demonstrated under practical conditions.

1. Twenty-eight calves fed reconstituted buttermilk for 20 days and then concentrates, hay and water were allocated to 4 treatments consisting of the addition of chlortetracycline to both the buttermilk and the concentrate mixture, to the buttermilk alone, to the concentrates alone, or to neither.

2. Live-weight gains from 3 to 28 days and the incidence of scouring were not affected significantly by any of the treatments.

3. The addition of chlortetracycline to the concentrate mixture increased significantly: (a) rate of live-weight gain from 28 to 56 days and from 56 o t 84 days: (b) skeletal growth from 3 to 84 days: (c) the consumption of concentrates from 14 to 56 and from 14 to 84 days; and (d) the concentrate conversion rate.

4. The addition of chlortetracycline to the buttermilk had no significant effect on any of the above measurements neither did it make any significant difference to the effect of adding chlortetracycline to the concentrate mixture.

5. There was a direct relationship between quantity of concentrates consumed on the one hand, and rate of live-weight gain and efficiency of conversion of the concentrate, on the other. None of the treatment effects was significant after the data were corrected for differences in the quantities of concentrates consumed.

6. From the results of this experiment and from evidence in the literature it is postulated that one of the effects of feeding antibiotics to calves is to reduce the fermentative activity of rumen bacteria and consequently the amount of gas produced in the rumen, the net result being that the antibiotic-fed animal eats more food and hence grows more quickly.

1. Ninety-six Large White fattening pigs, 8-10 weeks old at the beginning of the trial were used to study the effects of ultra-violet irradiation (22½ hours daily) with and without oxytetracycline supplements of the diet. All meal fed was fortified with vitamin D.

2. Under the conditions of this trial ultra-violet irradiation was without effect. Oxytetracycline supplementation resulted in significantly higher live-weight increases, lower age at slaughter and improved feed conversion.

3. No significant treatment differences were recorded for any of the carcass measurements.

4. Ultra-violet irradiation did not reduce the number of ‘thumping’ pigs nor the degree of lung damage by virus pneumonia, whereas ‘thumping’ was significantly less on the oxytetracycline treatments.

5. The results are discussed in relation to vitamin D requirements and the presence of virus pneumonia.

1. Two groups of 12 Ayrshire heifer calves were reared from birth to 14 weeks on two contrasting systems.

2. The conventionally reared group consumed 19 gal. of milk, 86 gal. of milk substitute and 195 lb. of calf meal (17·0% crude protein in dry matter) in 14 weeks whereas the early-weaned animals consumed 5 gal. of milk, 19 gal. of milk substitute and 259 lb. of early-weaning cubes (22·7% crude protein in dry matter) in the same period and were weaned from milk substitute at 5 weeks old. All the calves had unlimited access to dried grass (12·0% crude protein in dry matter).

3. The mean live-weight gain of the calves on the conventional system was 1·26 lb./day and of the early-weaned animals, 1·20 lb./day. These values were not significantly different.

4. None of the experimental calves had bloat or indigestion and there was only one minor outbreak of scour.

5. At the present day prices of the foods, the early-weaning system was the cheaper system both per day and per pound of live-weight gain.

1. Sixty-four Blackface wether lambs, weaned some 8 days previously from the hill were divided into two similar groups. One group of lambs was implanted with 15 mg. hexoestrol.

2. The treated lambs had gained an average of 2·32 lb., and 3·88 lb. live-weight more than the control group, after 4 and 7 weeks respectively.

3. The mean carcass weight of 23 hexoestrol-implanted lambs was 1·5 lb. greater than that of the same number of untreated lambs.

4. Carcass grading provided no evidence of a deterioration in quality as the result of hexoestrol implantation.

5. Light lambs responded at least as well as heavy lambs to the hormone.

1. Wessex Saddleback sows were fed 4 lb. or 2 lb. of a balanced meal per head per day during the first 13 weeks after mating with a Large White boar. All sows received 6 lb. of meal for the last 3 weeks of pregnancy, and approximately 14 lb. (4 lb. plus 1 lb. for each piglet) during lactation. From mating to weaning half the sows on each feeding treatment had access to small soil pens, and the other half to range grazing of lucerne or grass/clover swards.

2. During the first 3 months of gestation sows on soil receiving 2 lb. of meal gained 20 lb. while those on grazing gained 40 lb., equal to the gain of sows fed 4 lb. of meal.

3. Approximately 10·5 piglets were born per sow under all treatments. Piglet mortality was highest with sows which had been fed 4 lb. of meal during pregnancy and were confined in small soil pens, because this treatment produced the greatest number of over-fat sows. Mean piglet weight at 3 weeks (≏ 12 lb.) and 8 weeks (≏ 39 lb.) and total creep-fed meal consumption per piglet (≏ 30 lb.) were similar for all treatments.

4. In a preliminary trial 3½ lb. of dried grass plus ½ lb. of meal per head per day was fed to gilts during the second and third months of pregnancy without adversely affecting farrowing results.

5. From these experiments and the published work it is suggested:—

(a) Pasture alone would probably have been sufficient during the second and third months of pregnancy of the sows used in these trials.

(b) Feeding standards for pregnant sows of 250-350 lb. live-weight may be too generous, and produce ‘fat not fit’ sows at farrowing.

(c) In practice the reduction of meal feeding and the greater dependence on grazing should be applied individually to each sow according to her condition and response.

1. Three measurements on both sides of 15 carcasses and 5 additional measurements on bot h sides of 6 carcasses were taken in duplicate by 3 observers working independently. The carcasses, which ranged in weight from 520 to 884 lb., were measured from 2 to 6 hr. after slaughter while on the hook in the chill-room of a slaughter-house.

2. Length of body and loin were the measurements which could be taken the most consistently, whereas the 2 depth measurements and the length of tibia were the least repeatable.

3. For 2 measurements, there were marked differences between observers i n the average differences between sides. In all carcass investigations, measurements should be taken on both sides and averaged.

4. For all measurements, except the length of body and loin, there were differences in the average values found by the 3 observers.

5. It is suggested that to achieve a satisfactory degree of repeatability, slight redefinition and clarification of the points of reference is required for some measurements, whereas others may have to be discarded.

Sixty-five pairs of two-egg cattle twins of three breeds, Ayrshire, Friesian, and Shorthorn, were split at random within a week of their birth between two groups of commercial dairy farms. One group was selected for a relatively high average milk yield of the adult dairy herd (group A) and the other for relatively low average yield (group B). The body growth of the twins up to nearly 4 years old is described in this paper. Very significant differences in growth developed in consequence of the split between the groups. Twins on the A farms became larger than their co-twins on the B farms. Average differences between the groups increased for the first year or 18 months and then began to fall away, but had not disappeared at the last age (198 weeks) studied. The various body parts behaved differently i n response to the treatments or environments associated with the two groups of farms. Thus, at the ages studied, the twins on the ‘high’ yield farms differed in conformation from their co-twins on the ‘low’ yield farms. In addition to the differences arising between the members of split twin pairs, there were also differences in body size between the pairs. Breed was not apparently important as a factor affecting the growth differences arising between the two treatments.

1. Observations were made at 2 years of age on 25 freemartins and their castrated brothers. Three of the freemartins belonged to a set of 4-egg quadruplets. For comparison there were 93 normal pregnant twin and single-born heifers and 14 males twin to males.

2. Twelve body measurements on each animal were taken. Averages for each character for 25 single-born Ayrshire heifers and for 10 single-born Friesian heifers were used as standards for comparison with the various groups of twins of like and unlike sex, triplets, and quadruplets.

3. Normal twin heifers were slightly smaller in all respects than the standard. Freemartins were also smaller but more so. The quadruplet freemartins were smaller still, but at 2 years they had the live-weight of normal heifers only 1½ years old. Twin males, whether from like or unlike-sexed pairs, were on average slightly smaller than the standard.

4. Percentage deviations of each group mean from standard varied systematically when characters were listed in a pre-determined order based on earliness of maturing. This relation has been summarised for each group by the regression of the percentage deviation on order of maturity, the order beginning with head width, and ending with the widths of hooks, pins, and chest. Each available group differed significantly from the chosen standard in conformation in such a way that the later a character appeared in the order, the less it exceeded, or the more it fell short of the standard.

5. As judged by the size of these regression coefficients, males twin to males showed the greatest difference in conformation from normal single-born females. Males twin to freemartins showed a slightly smaller difference. Freemartins were intermediate but closer to males. Fertile twin females and single-born females differed very little. These relations held at both 2 years of age and a live-weight of 650 lb. (1½ to 1½ years).

6. The quadruplet freemartins were anomalous in having the linear dimensions of immature normal instead of freemartin females of the same weight as if their early maturing body characters had been permanently retarded during slow growth before and after birth.

Evidence of an effect of the peck order in poultry on the variation in productive characters under floor conditions is used as the basis of a discussion on the design of animal experiments.

Since these competitive effects increase the variation between animals penned together, the usual tests for the presence of pen effects between replicate pens are unsuitable. Replicates should be used in all experiments when treatments are allocated to pens of animals to provide an adequate measure of the experimental error.

Considerations of social behaviour are likely to be relevant in many types of animal experiments, both husbandry and breeding.

It is, however, emphasised that the amount of information available on such an important question is completely inadequate and that behaviour studies should be incorporated into all types of animal experiments to obtain such information.

The effects of birth weight, maternal age and parity on survival of single lambs have been studied in a Blackface and a Welsh Mountain flock.

In both flocks the maximum survival rate was found to occur among lambs with birth weights just above the mean. Mortality increased as lambs' birth weight increased or decreased from the optimum, but was especially heavy at the lower extreme of the range of birth weights.

Mortality decreased with age of dam to 14·3% for lambs from 4- to 6-year-old Blackface ewes and to 9·4% for lambs of 3- to 4-year-old Welsh ewes. Ewes having their first lambs gave mortality rates twice as great as for the mature ewes in the same flocks. The lower chances of survival of first born lambs irrespective of dam's age accounts for the apparent trend of mortality with maternal age in the Blackface.

Changes in mortality rates associated with variation in lamb's birth weight and with the age structure of the ewe flock were estimated. Possible means of improvement of survival rate are discussed.