Pelvic Growth and Dystocia in Holstein X Hereford Heifers

Abstract

Growth of the pelvic area and relationship to external pelvic measurements was monitored in 129 Holstein X Hereford heifers fed an all forage diet. Pelvic area increased at a rate of .27 ± .20 cm2/day from 10 to 16 months and a rate of .13± .13 cm2/day from 16 to 22 months (p < .01). A moderate correlation between pelvic area and external pelvic measures (body weight, height at hooks or pins, distance between hooks and hooks to pins) was noted (R² ≤ .15 - .38, p < .01) and the relationship did not change with age. In 76 of these heifers, pelvic area was measured within 24 hours of calving. From 22 months to calving, pelvic area increased at the rate of 1.15± .88 cm2/day. This was 7 times greater than the rate observed from 16 to 22 months (.13± .13 cm2/day). While pelvic area at calving had a significant correlation to pelvic area measured prior to calving (p < .01) correlations were low to moderate (R=.29-.52).

The influence of pelvic area and calf birth weight on incidence of dystocia were modeled with both logistic regression and discriminant analysis techniques. Neither was superior, both correctly predicting 72% of cases. While ratio of pelvic area at calving to calf birth weight significantly (p < .01) influenced the incidence of dystocia, pelvic area measured at any time other than calving was not associated with dystocia (p > .05). The low correlation between pelvic area at calving and precalving measurement was due to the high degree of variation noted in pelvic growth. As a result, we were unable to predict dystocia by measuring pelvic area prior to calving.