In pasture research and feeding trials using the growing or fattening animal to provide a measure of output, a first essential is the accurate determination of liveweight. Recent reports of trials using bullocks, sheep and dairy stock (Grassl. Res. Sta. Rep., 1953; Waite et al., 1952; Dodsworth and Campbell, 1953) have emphasised that liveweight gains can be misleading when a large and unknown proportion of the gain is due to contents of the stomachs and intestines. This ‘ fill ’ in the capacious alimentary tract of the ruminant provides a large source of experimental error in the measurement of liveweight; it can also obscure the trend of useful liveweight gain, i.e. carcass increase.

There is little doubt that the lowest costs of beef or milk production are achieved when the animals are grazed on pastures from which they obtain most or all of their sustenance. On the other hand the most expensive phase of cattle production is the winter period when stock are usually housed and must be hand-fed. The results from numerous investigations firmly support these assertions. In the large mixed farming area of the North-East of Scotland virtually no grazing is normally available from the middle or end of October until the beginning of May when normal grass growth has resumed.

Seasonal variations in the milk production of a dairy herd are due to the seasonal distribution of calvings, to changes in the potential productivity of the herd due to effects of age, and to seasonal changes in the herd environment.

This is a preliminary report of an attempt to estimate the effect of these seasonal changes in climate, feeding and management upon milk yields during single herd years, by making adjustments for the effects of the calving distribution and changes in potential productivity. Milk records from two Dairy Shorthorn herds were used.

This paper is a report on preliminary work carried out at the Rowett Research Institute during the winter of 1951-52, in cooperation with Mr. Gill and Mr. Thomson.

What is known as stratification of the sheep industry in Scotland is the differentiation of enterprise into fairly distinctive types, roughly according to the altitude of the holdings. In the production of mutton, four main types of enterprise are concerned:—

• (1) breeding of hill ewes for replacement of hill stocks

• (2) breeding of first-cross ewes

• (3) breeding of second-cross lambs

• (4) fattening of second-cross lambs.

The importance of feeding the ewe well during pregnancy and lactation has long been realized, but differences of opinion exist as to what stage food, in addition to natural grazing, should be given. If, for example, a farmer had a limited supply of supplementary food, when would it be best to feed it? The answer to this question is dependent on factors such as breed of sheep, the expected lambing percentage, the grazing available and the weather conditions.

The efficacy of three sources of vitamins A and D supplements was tested in an experiment with fattening pigs involving the following four treatments :

• (1) Control—basal meal.

• (2) As control, but at one week of age the pigs had been given a single intramuscular injection of a commercial preparation, supplying 500,000 i.u. of vitamin A and 100,000 i.u. of vitamin D3.

• (3) Basal meal + 1 % cod-liver oil (containing 500 i.u./g. of vitamin A and 68 i.u./g. of vitamin 3), supplying 2,270 i.u. of vitamin A and 309 i.u. of vitamin D3 per lb. of diet.

• (4) Basal meal + synthetic vitamins A and D concentrate (containing 50,000 i.u./g. of vitamin A and 5,000 i.u./g. of vitamin D3), added to supply 2,250 i.u. of vitamin A and 300 i.u. of vitamin D3 per lb. of diet.

The basal meal which was the standard fattening diet used at Shinfield consisted of: fine miller’s offal 50, barley meal 30, flaked maize 10, white fish meal 10, all parts by weight. It should be noted that the diet contained a precursor of vitamin A, and it was calculated that this would provide about one-third of the recommended allowance of vitamin A for fattening pigs.

Dividing the meat carcass into its three main component tissues, bone, muscle and fat, it is known that they develop in a well-defined order, bone being the earliest maturing and fat the latest (Hammond, 1932). Of the three, muscle is the most important from the viewpoint of human nutrition and the factors influencing its growth obviously demand serious consideration. The literature on qualitative growth contains numerous references to microscopical meat studies, but, due to the diversity of conditions under which the observations were made, the results obtained cannot easily be co-ordinated. An investigation was therefore planned in which most of the major factors influencing growth and development of muscle in general, and the muscle fibre in particular, could be studied.

The number of breeding sheep in a flock and the number of generations under selection will directly affect the genetic improvement possible. Both in cattle (Donald and El Itriby, 1945, 1946) and in pigs (Donald and Auerbach, 1942) a small average herd size and short life were found to have set severe limits to the breeding policies possible. The present report discusses this problem in lowland registered sheep flocks.

An experiment, designed to determine the extent of the maternal influence on size in sheep, in which groups of Border Leicester and Welsh Mountain ewes were bred to rams of both breeds, has shown that the nature of the maternal environment had a relatively small effect on the size of lambs at birth and on their subsequent growth. The maternal influence on a late-maturing character (liveweight) was larger than on an early-maturing character (’ cannon-bone’ length), but the effect of heterosis on the late-maturing character was greater still and tended to overshadow the maternal effect.

Body length has long been emphasized by the Scandinavian breeders as being of paramount economic importance in the selection of pigs for the British market. (Rozycki; Jespersen and Madsen ; cited by Smith and Robison, 1934). The development of strains or breeds of pigs possessing some uniformity regarding body length may well assist materially in producing at home the type of bacon which the British housewife needs instead of the continued importation of such bacon from those countries which have for so long dominated our markets. The difficulty of assessing in the live pig what its carcass grade will be, or of forecasting in the weaner its potential quality as a baconer, calls for scientific investigation into the ways and means of doing this, particularly for the selection of pigs for breeding and improvement policies.

The main object of the artificial insemination service is herd improvement. This is facilitated by the larger selection differential obtained when only a small number of bulls are used. Robertson and Rendel (1954) have shown that artificially bred daughters by bulls used at centres outwith the Milk Marketing Board system did not outyield naturally bred daughters milking in the same herds and these results have been substantiated by data from the Board’s centres. This failure to select bulls better than those used in the average herd has probably been due to the multiple aims of selection necessary to satisfy all those interested in the artificial breeding movement and to the methods which have been used to evaluate bulls. A method has been designed aimed at improving this evaluation.

There are two schools of thought concerning the most appropriate environment in which to select breeding animals. One says ‘ Always select animals under environmental conditions similar to those where they are to be used ‘. The other says ‘ Select breeding animals in the optimum environment so that they have the best chance of revealing their genetic capabilities ‘. Experiments on growth of laboratory mice and experience with European cattle in the tropics have shown the advisability of the first course in these cases. In regard to hill sheep and dairy cattle in Britain, on the other hand, practice favours the second course, but there is little experimental evidence to support it.

Existing information about the effect of inbreeding on production characteristics in dairy cattle leaves much to be desired. Sources are two-fold ; from experiments specially designed to get information on this and other aspects of inbreeding and also from the analysis of records made in closed herds. However, the experiments are few and in many of the second type of analysis the degree of inbreeding is not high. Furthermore, an examination of the detailed results in one breed, Holstein-Friesians in the U.S.A., shows little agreement in the results obtained. While agreeing in finding a decline in production as inbreeding progressed, the different investigators disagreed as to the magnitude of the effect. Even under ideal conditons, one should perhaps not expect too close an agreement because the genetic situation may well be quite different in the initial stock in the different experiments and genetic drift during inbreeding may further obscure the picture. In addition, if the inbreeding each generation is small, any selection that is practised may complicate the situation. Most of the programmes of deliberate inbreeding were not started simply to investigate the effects of the breeding system but rather to try to produce superior inbred stock.

The purpose of this experiment is to compare, under identical rearing and management conditions the performance of steers of certain dairy and dual-purpose breeds with steers by beef bulls out of these same breeds.

The animals are reared, fattened and sold to the best advantage at reasonable weights and condition, and the carcasses examined and as much information obtained on carcass weights and measurements as the slaughtering and disposal conditions allow.

To those engaged in the improvement of livestock the problem of the generation interval needs virtually no introduction. In mammals, the generation interval consists of two well-defined phases :

• (a) the interval between birth and sexual maturity and

• (b) the gestation period.

Whereas the length of gestation within a species is a relatively fixed period subject only to minor variations, the ages at which puberty and sexual maturity are attained are very variable, being influenced both by genetic and environmental factors. Thus, breed, strain, season of birth, plane of nutrition and system of management all contribute to determining the onset of puberty and eventual attainment of sexual maturity.

Selection work with the Rhode Island Red breed, involving the extensive collection of records, was first started at Wye College in 1948. Since that time the methods of selection employed have changed substantially in the light of the experience gained and the scheme, as it is operated at present, is shown diagrammatically in Fig. 1.

Sixty full-sister groups are recorded from first egg to the end of November. At least three full brothers of each of these sister groups.