Dystocia in relationship to size and shape of pelvic opening in Holstein heifers

One hundred twenty-seven Holstein heifers were measured prior to calving to obtain 1) heart girth and 2) the horizontal and vertical pelvic measurement, from which pelvic area was calculated. Dystocia scores were assigned at birth, and the heart girth of the calf and sex of the calf were recorded. There was no difference in the level of dystocia noted in heifers with different pelvic sizes. The major cause of dystocia was size of the calf. A greater proportion of the larger calves was bulls (29% vs 20%). The shape of the pelvic opening may affect dystocia through increased calf size.

Ninety-three pregnant heifers were measured on two or more occasions at approximately 60-day intervals to obtain 1) the heart girth and 2) the horizontal and vertical measurements, from which pelvic area was calculated. These measurements were used to determine heifer growth. The heifer's heart girth grew at a rate of 0.066 cm per day of gestation with a corresponding increase in pelvic area of 2.25 cm² per cm of heart girth, or 0.312 cm per day of gestation.