Biological and economic evaluation of different weights at weaning of crosses Dorper and Southdown lambs in restricted grazing on Red clover and Chicory

Abstract

The effect of weaning weight (low: 20; average: 25 and high: 28 kg) and the genotype (cross Southdown or cross Dorper) on growth rate, slaughter weight and body con­dition was studied in 60 lambs. The experiment was con­ducted in summer during 119 days and the lambs had restricted access to a pasture of Trifolium pratenses and Cichorium intybus. The grazing time was from 19:00 un­til 07:00 hours. The rest of the time, the lambs remained confined and received whole sorghum grain as supple­ment (first 48 days) and sorghum + soybean pellets in a 60:40 rate (last 71 days), that was offered to all animals at 1% of the body weight, adjusted weekly. The stocking rate during the 119 experimental days was 20 lambs/ha. Since the live weights effective at the beginning of the ex­periment were greater (p≤0.0001) than those established for weaning (23.4 kg, 26.0 kg and 28.4 kg, low, average and high weaning weight, respectively), no significant difference was observed between groups regarding daily weight gain during the experiment or economical result. Unlike the weaning weight, the genotype used had biolog­ical and economical response. Southdown lambs present­ed better (p≤0.01) biological behavior: + 25 g/day/lamb and better economical result: + US$ 3.8/lamb, during the experimental period, once they were compared to their Dorper contemporaries. The genotype used for terminal crosses is relevant if the lambs are marketed with high weights (≥ 34 kg).