A STUDY OF SOME OF THE FACTORS INFLUENCING EASE OF CALVING IN RANGE BEEF HEIFERS

Abstract

This study was performed in two parts. In the first part, 349 calving records of 2-yr-old heifers in 1979, 1980 and 1981 were analyzed by least-squares to assess the effects of lowering sire birth weight on calf birth weight and ease of calving. The study demonstrated that using sires with lower birth weight in 1981 compared to 1979 and 1980 (31.12 vs. 40.12 and 40.17 kg, respectively), reduced the average calf birth weight (32.65 vs. 36.04 and 34.62 kg, respectively) which in turn improved calving performance of the heifers in 1981 compared to the previous years. In the second part, 128 calving records of 2-yr-old heifers in 1981 were analyzed to study the relative importance of hip height, area of pelvic opening, condition score and weight at calving on calving performance. The results indicated that heifer weight at calving had a significant influence of calving performance (P < 0.01). Calving performance improved with increases in heifer weight at calving. Height at hip was phenotypically correlated with weight at calving, area of pelvic opening and calf birth weight. Phenotypic correlation between weight at calving and area of pelvic opening was also highly significant. The area of pelvic opening might exert a threshold effect on calving performance in 2-yr-old heifers. Key words: Cattle, dystocia, range beef heifers