1. The area of eye muscle cross-section of beef carcasses may be accurately measured by tracing the boundary and measuring the tracing with a planimeter. Taking a single area measurement from each of duplicate tracings increases the accuracy by some 30%. If a planimeter is not available, the area may be estimated by superimposing a grid on the tracing and counting squares; although this method is some 25% less accurate than the planimeter method it is sufficiently repeatable for experimental use.

2. Area estimated by combinations of linear measurements is highly repeatable, but predicts true area with insufficient accuracy for experimental use. The standard error of prediction is about 7% of the mean area. Regression equations relating planimeter area and combinations of measurements for various cuts and animals are given.

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.

Of 168 pronucleate ova recovered from sows killed at varying intervals after mating (0, 24, 30 and 48 hours), 20 showed more than 2 pronuclei; 19 of these were recovered from sows in which mating was delayed until 30 to 48 hours after the onset of heat. Evidence is presented that polyspermic fertilisation is responsible for the appearance of ova with more than 2 pronuclei. It is concluded that delayed mating increases the frequency of polyspermic fertilisation in pigs and this might be a source of embryonic mortality in pigs inseminated artificially.

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.

The relationship of six-month weight of sheep to their subsequent performance has been studied in a Scottish Blackface flock. The various aspects of performance considered were—live-weight of the ewe at tuppings, mortality and culling rates, fleece weight, lambing and weaning percentages and weight of lamb weaned. The regressions of these characteristics on sixmonth weight all declined with increasing age of the sheep and in any case only tupping weight, fleece weight and weight of lamb weaned had an association which was statistically significant. The results for each year of life of the sheep (up to drafting age at 6½ years) were subsequently combined to show how the total production of a flock of 1,000 ewes was related to the weight of the hoggs.

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.

Using extensions to Robertson's (1957) method for finding the optimum test design, factors affecting the improvement from testing were studied. Other than the heritability, the ratio of the number tested (N) to the number required for breeding stock (T) has the largest effect on the improvement expected, the improvement being roughly proportional to the logarithm of this ratio. The type of family and the number in the test group which compose the optimum design, also depend largely on the ratio N/T. Accuracy in evaluation is required when only few animals are selected (N/T high), but small test groups from large families are necessary when large numbers of breeding stock are required (N/T low).

Testing schemes differ basically in their selection procedure and only secondarily in their designs. The advantage resulting from the tested animals being themselves selected is in proportion to what part they constitute of the total selected.

Another consideration is how the testing is integrated with the population breeding structure. Maximum improvement will be obtained if the testing facilities are restricted to a nucleus group of breeders, and full opportunity for selection is made in their stocks. The increased improvement this providesis accumulated in this nucleus group of herds and gradually passed down to the rest of the herds. Otherwise the improvement will be greatest when each breeder can use sires from families which have performed well in thetesting.

Carcass measurements made on 1,463 Large White pigs from 88 inbred lines, at various degrees of inbreeding, have been analysed.

Partial regression coefficients calculated within lines showed that each 10% increase in inbreeding coefficient significantly increased carcass weight by 0·46 lb., decreased mid-back fat thickness by 0·37 mm. and streak thickness by 0·36 mm.

Partial regression coefficients calculated on all the material, or on line means showed, however, that the most highly inbred pigs tended to be shorter and fatter than average. Possible explanations of this finding are discussed and it is suggested that under the selection procedure adopted for litter size and weaning, weight favours the survival of these less desirable lines.

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.

The back fat thickness of 77 live pigs has been measured with an ultrasonic instrument. The method is simple to use and the ultrasonic waves do not harm the pigs. For measurement of a pig on one day, 95% of the mean ultrasonic readings are within ±13·2% of the mean measurements on the carcass.

Evidence for variations between the breeds examined or between sexes is doubtful. By taking repeated measurements on a large number of days, the accuracy of the mean readings for a pig would approach the limit inherent in the method. This limit is determined by small differences between pigs and is estimated to be within ±4·2% for 95% of pigs.

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.

1. 768 lambs on fourteen farms in the north-east of Scotland were divided into a control group and groups receiving two 5 mg., three 5 mg., two 7·5 mg., and one 15 mg. pellet of hexoestrol.

2. On every farm the mean rate of live-weight gain of the treated lambs was greater than that of the controls.

3. There appeared to be very little difference between implantations of two 5 mg., three 5 mg. and two 7·5 mg. pellets of hexoestrol but on four farms where a direct comparison was made one 15 mg. pellet was slightly inferior to three 5 mg. pellets.

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. Data from 208 piglets in 24 litters were examined to evaluate the relationships of weights at 3 and 8 weeks with birth weight and milk consumption within litters, and with these and creep-feed consumption between litters.

2. Of the total variation in 3-week weight within litters, 39% was associated with variation in birth weight, 67% with variation in milk consumption to 3 weeks, and 80% with these two factors combined. Of the total variation in 8-week weight within litters, 30% was associated with variation in birth weight, 25% with variation in milk consumption to 8 weeks, 42% with these two factors combined and 45% with variation in 3-week weight.

3. Of the total variation in 3-week weight between litters, 6% was associated with variation in birth weight, 15% with variation in milk consumption to 3 weeks, and 18% with these two factors together. These values were all too low to be statistically significant, as were the equivalent relationships with 8-week weight. Of the total variation in 8-week weight between litters, 77 % was associated with variation in creep-feed consumption to 8 weeks, 70% with variation in 3-week weight, 85% with consumptions to 8 weeks of milk and creep-feed combined, and 89 % with creep-feed consumption to 8 weeks and 3-week weight combined.

4. The practical significance of these relationships is discussed.

1. Eighteen pairs of one-egg and 6 pairs of two-egg twin calves were used in a balanced incomplete block design to examine four systems of rearing: (1) a continuous high plane of nutrition from birth to first calving (HH); (2) a high plane for the first 44 weeks followed by a low plane until 2 months before calving (HL); (3) a continuous low plane until 2 months before calving (LL); and (4) a low plane to 44 weeks followed by a high plane to first calving (LH). All animals were fed on a high plane during the two months before calving.

2. Mean daily consumptions of DM, TDN, S.E. and DCP are given and the net energy intakes compared with a recently recommended standard.

3. At 44, 80 and 104 weeks of age there were highly significant differences between the groups in all weights and measurements due to treatment. Low-plane feeding retarded the growth of the skeleton to only a limited extent as compared with live-weight. After the changeover, animals on the HL system lost much of the advantage in body measurements they had gained over those fed on a continuous low plane.

4. All groups reached sexual maturity at the same stage of physical development but at different ages. The HL animals were the slowest to attain maturity indicating that as with growth the changeover from a high plane to a low plane of nutrition had had an adverse effect.

5. Low-plane animals on poor hill pasture made better growth than their mates on good arable pasture. Evidence is presented, however, to show that part of this greater growth in live-weight was due to increased ‘fill’.

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.

Groups of Dorper lambs were castrated at three ages: shortly after birth, and at two and four months of age. All were slaughtered at an age of six months and the carcasses subsequently weighed, graded, measured and scored. The results indicate no marked differences in either weight or quality of carcass between the treatments. It is concluded that the operation can safely be carried out, depending upon circumstances, at any stage between birth and four months.

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.