Determination of prediction equations for estimating body weight of Zulu (Nguni) sheep

Abstract

Data on linear body measurements (LBM) of 403 sheep collected in three areas of KwaZulu-Natal were utilized to develop a prediction equation for live body weight of Zulu sheep. Data were collected on live weight (LW), heart girth (HG), wither height (WH) and scrotum circumference (SC) on sheep of all ages. The age of sheep was estimated by dentition. The analysis of variance showed that age and sex were important factors contributing to variation in LW of Zulu sheep. Phenotypic correlation coefficients and regression equations of LW on HG, WH and SC were computed within different age groups (milk set of teeth, one pair, two pairs and the three and four pairs of incisors). Low correlation coefficients ( r = 0.21–0.48) between LW, HG and WH were found among the pregnant ewes. The relationship between LBM and LW was stronger ( r = 0.66–0.86) for males than among females ( r = 0.42–0.75). The cubic polynomial of HG was the best fit ( R 2 = 0.76) for the live weight prediction of young sheep with milk set of teeth. The combination of HG and WH produced the best fit for the two tooth and above males and non-pregnant females. The LW prediction equations for pregnant females were not reliable ( R 2 = 0.05–0.26). The SC was more precise ( R 2 = 0.61–0.80) when estimating the live weight of young males (<15–22-month-old) than of the older rams ( R 2 = 0.23–0.56). It was concluded that LW of Zulu sheep can be reasonably estimated using the HG and WH. A table could be constructed for the farmers to estimate the LW of their animals.