Estimation of Parameters of Growth Curve and Their Heritabilities and Genetic and Phenotypic Correlations in Watish Lambs in Sinnar State, Sudan

Abstract

This study was carried out in Singa and Um-Benein localities. The first objective of this study was estimating the parameter of growth curve using Brody’s non-linear functions. And the second objective was estimating the effect of sex and type of birth on the growth curve parameters of Watish lambs. And the third objective was the estimation of heritability of growth curve parameters as well as estimation of genetic and phenotypic correlations among these parameters. A total number of 113 heads (N = 52 male and 61 females) of Watish lambs born to 65 ewes. This study was carried out during the breeding years 2021 and 2022 for this study. Each lamb consisted of lamb identification number (ID), dam ID, sire ID, approximate date of birth, sex of lamb, type of birth (single or twin), monthly body weight from day 1 and every 30 days up to 360 days of age. Non-linear (NLIN) procedure of SAS, was used to fit brody’s functions and to estimate the growth curve parameters. The A, B, K growth curve parameters which were asymptotic mature weight, proportion of weight gained after birth and weight gain per live weight per day respectively. These parameters were analyzed using model2 cross-classified non-interacting random sire effect and two other fixed effects, namely sex and type of birth and a random residual effect. The overall mean values of growth curve parameters A, B and K were 31.55kg, 0.88 and 0.51×10^-2, respectively. Effect of sex on parameter curve of watish lambs had a highly significant effect on K parameter (P≤0.01). Heritability for A, B and K parameters was 0.61, 0.00 and 0.12, respectively. These heritabilities were high for A and low for K and non-estimable for B. Estimates of genetic correlation between growth curve parameters A×K and B×K were -0.29 and -0.68, respectively. They considered low for the former parameter and high for the latter. The phenotypic correlations between growth curve parameters A×B and A×K were 0.80 and -0.53, respectively. These correlations were both considered high with one negative value.