Performance of crossbred progeny of Trangie Fertility Merino and Booroola Merino rams and Poll Dorset ewes. 1. Lamb birth weight, survival and growth

Abstract

Merino rams of the Trangie Fertility and Booroola strains were joined to Poll Dorset ewes in single sire mating groups over 3 years. Forty sires produced a total of 1250 lambs in 885 litters from 451 ewes. Lamb birth weight averaged 4.1 kg, 80.8% of lambs survived to 3 days of age and growth rates to weaning (mean 93 days) averaged 289 g/day. Lambs with Trangie Fertility sires grew 15 g/day faster and were 1.3 kg heavier at weaning than those lambs with Booroola sires (P<0.001). There were no effects of sire strain on birth weight or lamb survival. Birth weight increased with dam liveweight in mid-pregnancy (P<0.001), and weaning weight and growth rate increased with dam liveweight at joining (P<0.001). Survival of lambs was predominantly a function of birth weight. Lambs weighing 4 kg at birth from primiparous dams had survival rates of 76% compared with 88% for lambs from multiparous dams (P<0.01). No lamb under 2.0 or over 6.3 kg survived, and 48% of deaths occurred within 1 day of birth. Dystocia, particularly of heavy, single-born lambs, caused 53% of observed lamb deaths. For the traits birth weight, lamb survival, weaning weight and growth rate, the direct heritabilities were 0.24 ¦ 0.10, 0.05 ¦ 0.05, 0.19 ¦ 0.10 and 0.12 ¦ 0.08 respectively; the corresponding maternal heritabilities were 0.08 ¦ 0.05, 0.05 ¦ 0.04, 0.05 ¦ 0.05 and 0.07 ¦ 0.05 respectively; and the common environmental effects among litter mates (c2) were 0.57 ¦ 0.08, 0.47 ¦ 0.08, 0.15 ¦ 0.08 and 0.13 ¦ 0.08 respectively.