This paper reports a paternal half sib analysis of data collected over 3 years to estimate additive genetic variance of growth between birth and 16 weeks in crossbred progeny derived from Down rams. The data were divided into two groups and pooled estimates of parameters obtained by two methods. The paternal half sib intra-class correlations varied between 0·017 and 0·057 depending on pooling group and method. It is suggested that such low correlations arise because (a) most of the lambs in the study were still sucking at slaughter, close to 16 weeks of age, and the trait measured is thus largely influenced by maternal milking ability (b) the selection practised in the Down breeds may have been effective and reduced genetic variation and (c) there is considerable inbreeding in the Down breeds.

In further analysis of data from four farms involving rams mated to more than one breed of ewe there was limited evidence of specific combining ability of growth between birth and 16 weeks of age for Welsh ewes compared to ewes of other breeds.

1. Total anatomical dissection data from 62 half carcasses of steers representing 6 breed groups differing in age and nutritional history, were examined with a view to establishing a basis for comparison of carcass composition of breed groups or of cattle from various treatments.

2. The results indicate that total muscular tissue might be used for comparative purposes in certain instances. Muscle weight differences could be examined independently of general size by adjusting to common muscle plus bone weights.

3. It is proposed that relative carcass composition is best assessed by use of two measures: muscle: bone ratio and percentage fat tissue in the carcass.

4. Muscle: bone ratio was shown to increase with carcass weight and after the effects of carcass weight had been statistically removed the influence of percentage fat on this ratio was negligible. The required adjustment to muscle: bone ratio for differences in carcass weight was estimated at 0·03 per 10 kg. increase in carcass weight.

5. Percentage fat in a carcass is proposed as an index of acceptability. The requirements of different markets in terms of this index would need to be established. Adjustment factors for percentage fat based on carcass weight would need to be established on a within group basis.

6. Relative growth coefficients for muscle, bone and fat, based on a logarithmic relationship with total muscle plus bone, are presented and were found to agree closely with those for swine and sheep. The magnitude of differential growth in body tissues indicated by the growth coefficients accentuates the necessity of making carcass composition comparisons at standard weights or following suitable statistical adjustments.

7. The implications of carcass composition assessment in beef breeding programmes are discussed.

The paper reports the results of experiments to study the effects of different levels of dietary protein on the performance and carcass quality of bacon pigs fed on a high-energy diet: (a) to make similar rates of live-weight gain on all treatments, (b) to make similar rates of live-weight gain but with the level of protein on some treatments being reduced at 130 lb., (c) to allow ad libitum feed intake on all treatments, (d) to obtain two distinct

patterns of growth (fast-fast and slow-fast) on each of two levels of dietary protein.

In the comparison of the two contrasting patterns of growth there was no significant interaction between rate of gain during the period 40–125 lb. live-weight and level of dietary protein. Differences in carcass density and linear measurements were significant and the results suggest that irrespective of growth pattern there was a carcass response to level of protein.

Where diets of different protein content were given ad libitum or to obtain a uniform growth pattern on all treatments, growth rates were generally good, with little difference in feed intake between the treatments within each experiment; variations in level of protein therefore had little effect on growth rate. In some of the comparisons, significant carcass differences were found in terms of density, dissection data and linear measurements; in others only the density differences were significant.

The results suggest that with each of the feeding systems a level of about 17% crude protein, associated with 12% fish meal, is more likely than lower levels to give lean bacon carcasses. In the one experiment in which the protein level was reduced at 130 lb. live-weight there was no marked effect on carcass composition.

The results of two experiments, involving 72 individually fed pigs during a growing period between about 40 and 200 lb. live-weight, indicated that a water allowance of 1½ lb. per 1 lb. meal in place of 2½ lb. water had little effect on the performance of the pigs or on carcass measurements. With unrestricted water there were considerable differences in intakes between experiments but these were without significant effects on the criteria studied, when compared with the respective fixed water to feed ratios.

In the first experiment, but not in the second, a dietary supplement of penicillin was associated with a reduced voluntary intake of water. The penicillin was without overall effect on performance or carcass composition, but was associated with a significant growth response up to 100 lb. live-weight in the first experiment.

In both experiments females were less fat than castrates, as indicated by significantly different carcass densities and by some linear measurements.

If, from a population, samples of individuals are drawn with a small number of parents, it is shown that there will be on average an apparent excess of heterozygotes above the number calculated from the gene frequency in each sample. The apparent proportional excess is where M and F are the number of male and female parents. This is independent of the number of alleles at the locus concerned. The use of the usual significance tests will also be affected. If analyses are done within herds of domestic livestock, particularly cattle, the number of sires in use at any time is likely to lead to a bias of a size which is of biological importance. The conditions under which genotypic ratios can usefully be examined are discussed.

Although numerous studies on the early weaning system of calf rearing have given information concerning the composition of milk substitutes and concentrate rations which may be used, and the subsequent growth rates which may be expected, few have given information concerning either the relative effects on subsequent growth rate of initial weight, weaning weight, concentrate and hay intakes, or the relationships which exist among these factors themselves.

One of the causes of culling dairy cows is low milk yield and to the extent that this has any genetic basis one might expect the daughters of old cows to outyield their contemporaries from younger and hence less selected mothers. This is quite apart from any confounding effects resulting from the non-genetic influences of dams' parity. The rate of genetic improvement derived from the culling process will be modified within a population by the extent to which farmers choose to retain the progeny of older rather than younger cows. Milk yields for recorded cows in Scotland, available to the Livestock Records Bureau, have been used to obtain some information on these points.

The use of barley for intensive beef production, as described by Preston, Aitken, Whitelaw, Macdearmid, MacLeod and Philip (1963) is now a well established practice, but one of the hazards of this feeding system is bloat. There is evidence that the risk of this condition is accentuated if the barley husk is broken down too finely as happens if the grain is ground (Preston, Macdearmid and MacLeod, 1963; Preston, 1964). It was therefore recommended that barley should be processed in a roller mill and that the moisture content should be at least 16% (Preston, 1963), for if the grain is drier than this it is difficult to prevent excessive shattering and destruction of the husk. Suitable containers, which can be sealed in order to ensure anaerobic conditions and so overcome the problem of storing damp grain (greater than 16% moisture) have additional advantages at harvest since they can be filled quickly and easily. The purpose of this experiment was to evaluate the nutritive value of barley stored under these conditions.

1. Estimates of the voluntary feed intake of three age groups of wether sheep on ryegrass and white clover pasture from July to October, 1962, were made by total collection of faeces and the use of local faecal nitrogen-digestibility regressions.

2. Average faecal output and intake of digestible organic matter (DOM) increased with age of the sheep. However, relative to body weight (W) or to W073, the aged sheep (5 years old), which did not change much in weight over the period, consumed only about two-thirds of the DOM consumed by the younger (sixteen- and four-month-old) growing sheep.

3. For the growing sheep intake was directly related to weight. Intake was calculated to be 24 W (kg.)–28 ±108 g. DOM per day.

4. The results are discussed in relation to the errors in estimation of digestibility. Comparison of the intake estimates with other published data suggests there was a high apparent maintenance requirement. The voluntary feed intakes observed, when expressed as g. dry matter per kg. W0–73, were somewhat higher for young sheep but lower for aged sheep than estimates of previous authors.

By mean of egg transfer, lambs of a large breed of sheep (Lincoln) were born out of dams of a small breed (Welsh Mountain) and vice versa. One breed was approximately twice the weight of the other. The effects of this contrast in maternal environment upon the development of the wool follicles and upon subsequent wool production are described in this paper. These effects are compared with differences between singles and twins.

Data were obtained from skin and wool samples taken at birth and at 84 days post-partum.

Genetic differences were the largest single source of variation for most of the component characters of the skin and fleece.

Strong maternal influences were in evidence. These were shown to have affected both Lincoln and Welsh lambs in a general (average) way and also to have had different, specific effects on each genotype as shown by genotype-environment interactions. Differences in maternal environment following egg transfer, clearly affected follicle density, primary/secondary follicle ratio, fibre medullation, fibre diameter and fibre length. Wool production was not affected, apparently because reduced follicle density was associated with increased fibre length.

In the comparison between singles and twins the latter appeared to suffer a post-natal rather than a pre-natal restriction of secondary follicle development, and in the absence of extra fibre growth there was reduced wool production at 84 days.

1. Six Dorset Horn lambs were reared on each of four different concentrations of reconstituted full-cream dried milk powder (10, 15, 20 and 25 % dry matter). The lambs were fed to appetite four times a day for 3 weeks.

2. The lambs consumed significantly more liquid milk at the two lower concentrations. Intake of water per se increased with increasing concentration of dry matter.

3. There were no significant differences in the consumption of milk dry matter between the treatments, although there was a significant linear trend, with dry-matter intake decreasing with decreasing concentration.

4. There were no significant differences between the treatments in live-weight gain from 0 to 3 weeks or from 0 to 10 weeks.

5. There were no significant differences in the efficiency of feed conversion between the treatments.

6. Examination of the distribution of milk intake within days showed that the proportion of milk voluntarily consumed in the first feed of the day increased with age and with concentration.

7. The incidence of scouring was high, but there was no general relationship with treatment.

8. Abrupt weaning was not satisfactory for the lambs which had been offered only liquid food for 3 weeks and they had to receive a low level of milk feeding for a further week while they became accustomed to solid food.

This note describes the results of various analyses which were carried out to study relations between measurements indicative of the amount of fat and lean in the carcasses of bacon pigs and their weaning weights, rates of gain between weaning and slaughter, and the lengths of the carcasses. The data involved were taken from a series of experiments, the original purpose of which was to compare various feeding treatments used between weaning and slaughter (205 lb.). The interpretation of these analyses presents some difficulty because of the many ways in which variations in weaning weight, for example, may occur; such variations arise naturally (because of variations in genotype, mothering ability of the sow, etc.) or may be induced by changing methods of management (systems of feeding, housing conditions, etc.). Considerable caution should therefore be exercised in attempting to extend the relations discussed here to conditions outside their own context. The difficulties are emphasised by the variety of different results which other workers have reported on the effect of weaning weight on subsequent development (reviewed by Braude, 1964).

Genetic parameters were estimated among 26 traits in British Landrace bacon pigs. The data involved 2,296 pigs from 250 boars tested at the five British national pig progeny testing stations from 1959 to 1961 inclusive. Separate analyses were performed for each sex and for the litter totals, adjustments being made to the data for differences among periods within stations and for differences in age at start of test and in weight at slaughter. The genetic parameters were estimated from the sire components in a conventional hierarchical analysis of variance.

Estimates of heritability and genetic and phenotypic correlations among the 26 traits are presented and discussed. The parameter estimates were in very good agreement with figures obtained in a previous analysis with Large White pigs. They indicate that a large part of the variation and covariation among the 26 traits is genetic in origin, and the traits involved would change in response to selection. Moreover, with regard to their concurrent improvement there were no serious antagonisms in the genetic relationships among the traits studied. There was however, evidence of an interaction of sire and sex of progeny for nine of the 26 traits.

A principal component analysis was used in an attempt to summarise the correlations among the 26 traits. The first two components gave a reasonable fit to the correlation pattern and these were associated with fat depth, measures of muscling and dressing-out percentage.

1. Nitrogen balance studies were made on 8 Friesian steers given allconcentrate diets containing fish meal, soya bean meal, groundnut meal or cottonseed meal.

2. There were no differences in nitrogen retention but voluntary feed intake was significantly lower on the fish meal diet.

3. Adjustment of nitrogen retention to constant dry matter intake resulted in significantly higher values for the diets containing fish meal and cottonseed meal than for the others.

4. Rumen pH, rumen ammonia and blood urea were all much lower on the fish meal diet.

Birth weight was recorded in the first and second litters of six inbred strains of mice and of all possible crosses between them. The mean birth weight of F1 young was significantly greater than that of inbred young in most cases; in no case were they significantly lighter than inbred young at birth.

Foetal weight and placental weight were recorded on the 17th day post coitum in the first litters of four strains and of two pairs of reciprocal crosses. F1 foetuses were 13–16% heavier than inbred foetuses on crossing four strains. F1 placentae were about 15% heavier than inbred placentae on crossing three strains. Crossbreeding did not affect placental weight in the fourth strain. The significance of these findings is discussed.

Analyses of data from individual strains and crosses showed that foetal weight was affected by the number of implants in the same uterine horn and independently by the number in the whole litter. The two independent effects, local and systemic respectively, tended to decrease foetal weight as litter size increased. The independent local effect of litter size on placental weight was different and tended to increase placental weight slightly as the number of implants in the same uterine horn increased.

Three different instances of maternal effects on foetal and placental growth were observed.

The effects of the litter and the mother on foetal growth are discussed in relation to the physiological basis of environmental variation in pre-natal growth.

1. The effects of including small quantities of groundnut meal heavily contaminated with aflatoxin in the diets of calves and fattening cattle were studied.

2. Inclusion of 4% or 8% of the toxic meal in concentrate diets for early weaned calves significantly depressed live-weight gain and food intake prior to 3 months. The depression in live-weight gain was due to lowered food intake and to impaired food utilisation.

3. Inclusion of 4% to 12% toxic meal in meal mixtures consumed at 12–13 lb. daily for 20 weeks had no effect on the performance of fattening cattle.

4. Enlarged hepatic cell nuclei were found at slaughter in livers from calves which had received toxic meal and the incidence of these slight lesions varied with toxic meal intake. A very small incidence of similar lesions occurred in fat cattle fed on the highest level of toxic meal.

5. Complete exclusion of groundnut meals containing appreciable amounts of aflatoxin from the diets of calves and dairy cows, and its very limited use in diets for store and fattening cattle is recommended.

The extraction of sire proofs from non-orthogonal field data of the type met with in cattle A.I. populations presents special problems.

A weighted least squares procedure for the estimation of sire effects from data of this kind, cross-classified by sire and herd, is described. Expected Breeding Values computed from these estimates have certain optimum properties. The standard errors of the estimates of the Expected Breeding Values are derived. The method makes it possible to classify the sires into groups before the proofs are computed. This sub-division of the stud could be useful in young sire evaluation and in measuring genetic trends in the proven stud. The computations are readily programmed for a computer, and the assumptions involved in the use of the method are particularly well suited to A.I. progeny field data, especially where an annual draft of young sires is being tested. A worked example is given.