Genetic parameter estimates for total weight of lamb weaned in Afrino and Merino sheep

Abstract

Abstract A study was undertaken to estimate genetic parameters for total weight of lamb weaned in Afrino and Merino sheep. Data collected on the Carnarvon Afrino flock, the Carnarvon Merino flock and the Grootfontein Merino stud were used. For Afrino sheep, heritability estimates of 0.061 (0.043), 0.054 (0.055) and 0.170 (0.074) were obtained for total weight of lamb weaned after the first (TWW1), second (TWW2) and third (TWW3) parities respectively. Corresponding estimates for Carnarvon Merino sheep ranged from 0.090 (0.025) for TWW1 to 0.257 (0.047) for TWW4. Similar estimates of 0.084 (0.027), 0.045 (0.029), 0.132 (0.048) and 0.100 (0.054) were obtained for Grootfontein Merino sheep. High positive genetic (rG) and phenotypic (rp) correlations were estimated between first parity and lifetime reproductive performance in all three flocks. For the Carnarvon Afrino flock, rG increased from 0.609 (0.367) between TWW1 and TWW2 to 0.791 (0.206) between TWW1 and TWW3. The corresponding rp, however, decreased from 0.735 (0.019) to 0.613 (0.026). Similar decreases in rp from 0.708 (0.011) and 0.696 (0.013) (Between TWW1 and and TWW2) to 0.549 (0.017) and 0.510 (0.022) (between TWW1 and TWW4) were observed for the Carnarvon and Grootfontein Merino flocks respectively. Genetic correlation estimates of 0.866 (0.127), 0.913 and 0.736 (0.272) were obtained between TWW1 and TWW2, TWW3 and TWW4 for the Grootfontein Merino flock. The results of this study, obtained with two different breeds and in two different environments in flocks with a high and a low reproductive rate, indicate that selection for increased lifetime reproductive performance could be based on total weight of lamb weaned after the first parity.