Growth trajectory of Yiling sheep and its related genetic parameters

Growth traits are one of the focuses of sheep breeding, and growth curve is an effective method to describe growth traits. The body weight of Yiling sheep at 0, 120, 180, 360 and 540 days of age were fitted with five common nonlinear growth models: Logistic, Gompertz, Von Bertalanffy, Brody and Negative exponential, and the growth models were evaluated by goodness of fit standard. The results showed that the Von Bertalanffy model was suitable for characterizing the growth of Yiling sheep. The estimated values of parameters A(mature weight), B(scale parameter related to the initial body weight) and K(maturity rate) in Von Bertalanffy model were 82.88 ± 7.47, 0.64 ± 0.05 and 0.0048 ± 0.0010, respectively. The parameters of the growth curve of the Von Bertalanffy model were further utilized to estimate the inflection point body weight of Yiling sheep as 24.56 kg, and the inflection point age was 135 days old. The absolute growth rate(AGR) first increased and then decreased, reaching the maximum value of 0.1766 kg/day at 135 days of age. The relative growth rate (RGR) of Yiling sheep decreased with age. The mature weight of Yiling sheep was the closest to that of common meat breeds. The Least squares estimation showed that sex had a significant (p < 0.05) effect on the growth curve parameters of Yiling sheep, with rams having a greater mature weight than ewes, while ewes had a higher maturity rate. The heritability estimates of parameters A, B and K were 0.09, 0.04 and 0.01, respectively, and the negative correlation between A and K indicated that lower maturity rate could be selected to increase mature weight.