Birth weights, meningeal lesions, and survival of diverse genotypes of lambs from Merino and crossbred ewes

Abstract

The survival of 3530 lambs of 6 diverse genotypes (Poll Dorset, Texel, Border Leicester, and Merino sires) from Merino and Border Leicester Merino ewes was studied over 3 years at Cowra in New South Wales. Some of the matings involved laparoscopic insemination, which allowed gestation length to be recorded. Each mating group lambed in separate, adjacent paddocks, and birth weights, gestation length, lamb survival, and lamb autopsy data were collected. Breed of ewe significantly affected birth weight and gestation length. Lambs from Merino ewes were 0.3 kg lighter than those from Border Leicester Merino ewes and had a 2 days longer gestation. Both birth weight and gestation length varied significantly between years. Lamb losses to 3 days post partum were 11.3%, 20.8%, and 46.2% for singles, twins, and triplets, respectively. Meningeal lesions and presentation difficulties were associated with 66.6% of all deaths. The high incidence of lesions contrasts with a negligible incidence in some reports involving lean ewes and it is concluded that fatness of ewe may be implicated.