Maternal performance in sheep as affected by breed, crossbreeding and other factors

Abstract

SUMMARYMaternal performance of female sheep of three hill breeds, Scottish Blackface, Cheviot and Welsh Mountain, and the crosses among these breeds has been studied in terms of lifetime production and some of its components. The data are based on 193 ewes, which were given the opportunity of having four annual lamb crops, and their lambs.There was no significant variation among the breeds and crosses in ewe survival or in the proportion of barren ewes at each lambing. There was significant variation among the breeds and crosses in the number of lambs born per ewe lambing, in lamb survival and in weights of lamb at birth and at weaning. Crossbred ewes (producing crossbred lambs) had more and heavier lambs than expected from the average of the pure breeds contributing to each cross, but the three crossbred types differed in the amount of heterosis shown. Over their lifetime in the flock there were significant breed differences in the total weight of lambs weaned, with crossbred ewes producing about 9% more than the average of the parent breeds involved. The crossbred ewes produced more weight of lambs over their lifetime than pure Cheviot or pure Welsh Mountain ewes, but not as much as pure Scottish Blackface.Effects of parity of dam and of sex, birth type, and type of rearing of lamb are given.

Genetic parameters and factors influencing survival to twenty-four hours after birth in Danish meat sheep breeds

“…As expected from the results of previous studies, SB for all breeds was significantly affected by sex, with female lambs showing a greater SB compared with male lambs. Similar results for lamb survival at different ages from birth to weaning were found in different studies as well (Wiener and Hayter, 1975;Dalton et al, 1980;Burfening and Carpio, 1993;Southey et al, 2004). As mentioned by Petersson and Danell (1985), in all mammals, young males have greater risk of death compared with females.…”

The effects of breed, breeding system and other factors on lamb mortality: 1. Causes of death and effects on the incidence of losses

“…However, line-cross dams, like the most inbred class, were relatively few and produced only linecross lambs. Wiener & Hayter (1975) reported from an earlier generation in the same flock that inbreeding of lambs reduced survival by about eight lambs per 100 born but the effect was greatest for Blackface lambs and negligible in Cheviot and Blackface x Welsh lambs. In the present analysis there was no similar evidence of significant breed x inbreeding interactions.…”

“…The effects of breed, of lambs born, parity, management, nutrition and cross-breeding and inbreeding were further studied other environmental variables and a smaller number m relation to the causes of death as identified at of papers present information on causes of death, post-mortem examination. Other factors affecting Although these reports encompass many breeds and variation in overall mortality and the incidence of crosses of sheep, only a few can be interpreted as different causes are also examined, showing whether genetic variation contributes sig-An early finding in this flock was that both breed nificantly to lamb survival and even fewer papers a n d breeding system affected overall lamb mortality * Present address: Veterinary Investigation Centre, (Wiener, 1966;Wiener & Hayter, 1975) a con-West of Scotland Agricultural College, St Mary's In-elusion which was later extended in a study based dustrial Estate, Dumfries.…”

Lamb survival as affected by inbreeding and cross-breeding

“…However, there is no reason why such a mode of action would make the class with the highest estimated inbreeding rank higher than others with less inbreeding unless there is a threshold after which natural selection becomes operative. Wiener & Hayter (1975) speculated the operation of a threshold level of heterozygosity below which performance declines below expectation. They further indicated that this could be related to the environment.…”