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.

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.

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.

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.

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. 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.

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’.

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.

A simple but approximate method of pedigree evaluation is presented with particular reference to dairy cattle. It involves the expression of information available on any animal in the pedigree in terms of the equivalent number of ‘standard progeny records’. Formulae are given for the transfer of evidence from generation to generation within the pedigree. The application to one rather complex pedigree is illustrated and it is shown that the loss of information through the approximation is small.

Twenty-four Hereford × Angus × Shorthorn steers, which were 18 months old, were divided at random into four groups of six. There were four treatments, two involving the feeding of supplementary protein and two involving implantation of the steers with hexoestrol, thus:

(1) basic ration, no hexoestrol;

(2) supplementary protein, no hexoestrol;

(3) basic ration, hexoestrol implant;

(4) supplementary protein, hexoestrol implant.

While the hexoestrol implantation produced a significantly higher growth rate, the addition of protein, above the level in the basic ration, had no effect.

Blood samples from 262 Polish Red Cattle, 9 Danish Red Cattle and 123 cattle produced by crossing were examined for the presence of 45 erythrocyte antigenic factors.

The frequencies of most of the factors are given and estimates are made of the appropriate gene frequencies within the Polish Red breed as a whole.

Segregation of 42 B alleles was observed of which 9 have not previously been reported. The H′ factor hitherto recorded as marking an independent system is assigned to the SU system on genetical grounds and renamed S2.

It is concluded from the blood group data that the Polish Red breed has signs of a genetic relationship with Holstein-Friesian, Brown Swiss and Guernsey breeds but the relationship with the Danish Red breed is closer. The existence of the new alleles distinguish the Polish Red breed of cattle from all others investigated.