The relationship between prepartum dietary energy intake and pelvic area on dystocia

Abstract

This study in beef replacement heifers determined the relationship of prepartum dietary energy intake and pelvic area on dystocia. Beginning 100 d prepartum, Angus and Angus X Hereford heifers (n = 134) were allotted by breed, date of conception and body condition score (BCS) to either a low (7.53 Mcal ME/head/day; 66 head) or high (11.41 Mcal ME/head/day; 68 head) energy ration. Body weights (BW) and body condition scores (BCS) were taken every 28 d. Pelvic area was measured by one technician at three time intervals: yearling (11-12 mo), breeding (16-17 mo), and prepartum (24-25 mo). All heifers were artificially inseminated by one technician using semen from a Red Angus bull with a -4.1 birth weight EPD. Degree of dystocia was described by subjective scores (1 = no dystocia, 2 = easy pull, 3 = hard pull, and 4 = cesarean section). Data were analyzed by SAS procedures (SAS 1992). Stepwise regression with cow weight gain, pelvic area change (PACH) from yearling to prepartum, calf birth weight, calf sex and prepartum pelvic area (PPPA) explained only 12% of the variability in dystocia score (P > .05). When PACH, BCS at calving, and cow weight gain were individually regressed against the degree of dystocia, no variable accounted for more than 1.4% of the variability in the degree of dystocia (P > .05). Analysis of variance (ANOVA) indicated that prepartum energy level did not affect PACH from breeding age to prepartum (P = .29), similarly prepartum energy did not affect dystocia score (P = .2). The ANOVA model with cow weight gain, prepartum energy, calf sex and calf birth weight, and PPPA was significant (P = .078), as well as the interaction of prepartum energy and cow weight gain (P = .06). Least square means indicated that high energy - high gain females had higher dystocia scores (P < .05) than all other groups. These data suggest that dystocia score was affected by an interaction of prepartum energy level and weight gain in the dam and that calf sex, birth weight and prepartum pelvic area combine to influence dystocia intensity.