Genetic and Phenotypic Parameters of Early Growth Traits of Lambs Reared Artificially in a Controlled Environment

Genetic trends over 20 years of selection in the three synthetic Arcotts, Suffolk and Finnish Landrace sheep breeds. 1. Early growth traits

“…Estimates (+ SE) ofgenetic trends (1971-1990, and 1981-1990) without and with the use ofcontrol populations for lamb weights (kg yr'l) For personal use only. Lamb weights were corrected for age using a linear correction described previously by Shrestha and Heaney (1985) Data This study provides evidence that genetic variability, which exists for early lamb growth traits in multi-breed synthetic populations, can be utilized through artihcial selection to offer the sheep industry an effective practical means for rapid and permanent improvement of sheep productivity.…”

“…In the 1960s, imported and established sheep germplasm in North America was assembled into foundation breedins stock for the development of one specialized sire and tw6 dam strains Heaney 1985, 1987;Shrestha etaL 1992 Heaney et al (1982 (Shrestha and Heaney 1985 (Henderson and Quaas 1976 Earlier studies had shown that all first-order interactions were generally nonsignificant and, hence were excluded from the model. Lamb weights after birth were adjusted to a constant age by multiplying average daily gain, during the period under consideration, by the standard length of time in days plus birth weight or adjusted weights at successive ages.…”

“…L-ei valeurs correspondantes obtenues pour la Suffolk 6taient de 0,3, 0'4,0,4 et 0'5 kg ei pour ia Fi*oir" J. O,Z, 0,2,0,3 et 0,5 (Shrestha and Heaney 1985). Glnetic response to selection for growth rate may be enhanced by selecting lambs independently of their potential maternal effects and minimizing competition among litter mates for a fixed quantify of milk (Shrestha et al 1983 Lax et al 1979;Shelton 1979 …”

Research and technology for increasing the efficiency and output of lamb production systems

“…From 1984, information on the growth of half and full sibs was used in addition to individual performance in the selection index. Moderate levels of heritability estimates (0.25), for lamb weights under a controlled environment with artificial rearing (167), suggested that family selection should effectively improve the growth performance of ARC Strain 1, making it an alternative to existing meattype sire breeds. Selection in the synthetic dam strains is based primarily on litter size, with lesser emphasis on growth rate (heavier lambs within a litter are usually selected).…”

“…It should also be emphasized that the average litter size of the dam strains is superior to any contemporary domestic breed. (113) showed no significant effects of breed of sire on the weight of single cross and backcross lambs at weaning ( (27,28,129,167). Heterosis (the superiority of crossbreds over purebreds) for growth was significant both from weaning to 70 days, and from 70-140 days of age, for lambs reared artificially but only in the latter period for lambs reared with their dams.…”