Selection on linear size traits to improve live weight in Menz sheep under nucleus and village breeding programs

Ease of measurement of linear size traits is of particular significance in livestock breeding, particularly under village breeding programs where measuring live weight is difficult. In this study, we estimated genetic parameters and realized responses for live weight (LW) and linear size traits using data from an ongoing Menz sheep nucleus selection program. Using the estimated genetic parameters and simulating a nucleus breeding program and a village-based breeding program for Menz sheep, we compared predicted responses from indirect selection on linear size traits and direct selection on LW. Heritability estimates were 0.46, 0.36, 0.27, 0.31, 0.08, 0.48 and 0.23 for LW, wither height, body length, chest girth, pelvic width, tail length and tail circumference, respectively. Genetic correlations of LW with linear size traits ranged from 0.40 for tail length to 0.98 for chest girth. Realized responses in LW resulting from selection for LW and fleece weight in the ongoing Menz sheep selection program ranged from 0.27 to 0.86 kg per generation. Based on estimated genetic parameters, we chose chest girth, wither height and body length for the simulation study. Predicted responses in LW from indirect selection on chest girth, wither height and body length were 94.8% (nucleus program) and 92.6% (village program) of the responses to direct selection. Our results strongly indicate that genetic improvement in LW through indirect selection on linear size traits is possible both under nucleus and village-based breeding programs. Implications of results of simulated selection programs on the ongoing Menz sheep improvement program are discussed.