The maternal influence on size in sheep

Abstract

With Plates 1-3 and Sixteen Text-figures)Factors which affect the growth of the young animal are of great economic importance in animal production. In the past, much experimental work has been concerned with the effect on the growth of the young animal of different environmental factors. Many of these factors do not, however, affect the development of the young animal directly, but rather act on its maternal environment. Thus, much is known of the factors which affect the milk secretion of the female and this in turn is known to have a considerable effect on the growth of the young; similarly, the level of nutrition of the female during pregnancy has been found to influence foetal growth.The maternal environment may affect the growth of the offspring at two stages. Before birth, the foetus is entirely dependent upon its mother for its nutrition, so that foetal growth is subject to her control. After birth, the young animal is at first entirely dependent and, for a considerable period, is largely dependent on maternal care, or its equivalent, a most important feature of which is the milk supply available. The maternal influence may be defined as the sum of the effects of those maternal factors which influence the growth of the young after fertilization of the egg; it is made up of pre-natal and postnatal elements. Walton & Hammond (1938) and Joubert & Hammond (1954) have studied the effect of the maternal environment in horses and cattle respectively, by crossing breeds which differed greatly in size. Venge (1950) has studied the maternal influence on size in rabbits both by crossing breeds of markedly different size and also by transferring fertilized eggs between these breeds. The two methods used by Venge were also employed in the experiments to be described in this paper. These experiments were based on suppositions similar to those on which the above-mentioned earlier experiments with other species were based, namely, that breeds of ewes which differ markedly in size would provide different maternal environments, and that the cross-bred lambs would have similar genetic constitutions irrespective of which way the crosses were made. The control of body size and growth by sex-linked genes is thus assumed to be very small in relation to the main factors studied in these experiments.The two breeds of sheep which were selected for the present experiments were the Border Leicester and the Welsh Mountain; the live weight of mature Border Leicester ewes averages 140-180 lb., whilst that of Welsh Mountain ewes averages only 80-100 lb. In the first experiment, these breeds were crossed reciprocally so that (cross-bred) lambs having similar genetic constitutions were reared in the very different maternal environments provided by the two breeds of ewe; the effects on the size of the lambs of the two environments could then be compared. By using young and mature ewes, it was also possible to estimate the influence of the age of the mother on the size of the lambs. Thus the effects of (a) breed of ram, (6) breed of ewe, (c)...

Secretion of angiogenic activity by placental tissues of cows at several stages of gestation

“…By using various techniques (e.g. reciprocal matings or embryo transfers between breeds), it has been shown that the maternal genotype has a profound influence on fetal growth (Walton & Hammond, 1938;Venge, 1950;Hunter, 1956;Joubert & Hammond, 1958). In addition, the maternal system appears to have a limited ability to support fetal growth (Barcroft, 1946;McKeown & Record, 1953;Alexander, 1964;Anderson et al, 1978).…”

Maternal and sex-linked effects on size and conformation in domestic fowl

“…MATERNAL effects on adult size have been reported in several specie& of mammal (Walton and Hammond, 1938;Hunter, 1956;Joubert and Hammond, 1958;Brumby, ig6o). Their existence in birds is less certain, partly because the male (homogametic sex) is more troublesome to keep, and economically less useful, than the female.…”

Carcass Composition in Single and Multiple Birth Cattle

“…This fact was shown dramatically by Walton and Hammond [1938] who made reciprocal crosses between a very large breed of horses, the Shire, and a small breed of horses, the Shetland, and compared the foals. A similar study was conducted by Hunter [1956] who crossed the large Border…”