Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/1/1996
Publication Date: N/A
Citation: Interpretive Summary: Interest has developed in using pelvic measurements, with or without concomitant body measurements as tools to cull heifers that have a high probability of experiencing dystocia at parturition. This study suggests that obtaining these measurements in pregnant heifers after the end of the breeding season would be of little predictive value in Brahman-cross heifers. The finding that birth weight has a consistently important causative effect on dystocia in Brahman-cross heifers in this subtropical geographical region indicates producers must be aware that high birth weights will cause dystocia. This means that breeding programs for heifers must be based on keeping birth weights under control regardless of geographical region.
Technical Abstract: The study was conducted at Deseret Ranches, St. Cloud, FL. Body size data were obtained in 1991 and 1992 in mid-June (heifers approximately 17 mo old). Data included: hip height, heart girth, body weight, condition score (1 thinnest to 9 fattest), pelvic height, width and area. A total of 666 heifers were studied representing Red Brangus (B),Simbrah (S), and Braford (Br). All heifers were bred to Black Angus bulls. Calvings were scored, 1 = no to 4 = major difficulty. Post breeding body weights and pelvic areas by breed were: 304, 233; 330, 224; 344, 199 and 336, 188; 338, 199; 317, 190 kg and cm**2 for B, S, and Br, 1991 and 1992, respectively (breed effects for both weight and pelvic area, P < .01 for both years). Residual correlations between body weight and pelvic area were .20 and .35 (both P < .01) for 1991 and 1992, respectively. Dystocia incidence was 6.9% in 1992 and 10.5% in 1993 with males exceeding females in both years (1992, 10.6 vs 3.1%, P = .08; 1993, 15.6 vs 4.2%, P < .01 male vs female, respectively). Birth weights of males exceeded females 26.7 vs 24.3, 1992; 28.1 vs 26.1 kg, 1993, P < .01 both years). Calf birth weight was correlated with dystocia score in both years (r = .19 and .49 in 1992 and 1993, P < .05 and .01, respectively). Birth weight and dam heart girth and body weight (P < .05 to < .01) influenced dystocia in 1992, but only birth weight was significant (P < .01) in 1993. The regression of calving score on birth weight was curvilinear and significant with 30 kg birth weight being the approximate inflection point. We conclude, birth weight was an important and consistent factor in Brahman-cross heifers in this geographical region.