PSII-8 - Comparative evaluation of pelvic area measurements in dietary restricted heifers versus fully developed heifers

Abstract: Heifers with a small pelvic area have a higher risk of dystocia compared to those with a larger pelvic area. Assessing the pelvic area in heifers can be utilized for culling decisions. The objective of this study was to evaluate the pelvic area measurements between heifers developed on a restricted diet compared to fully developed heifers. Pelvic measurements were collected on 124 purebred Angus heifers from the Iowa State University McNay Memorial Research and Demonstration Farm outside Chariton, Iowa. Heifers were divided into two groups. The first group (G1; n = 61) were developed on a lower energy diet to 55% of mature body weight at time of breeding. The second group of heifers (G2; n = 63) were on a higher energy diet to achieve 65% of their mature body weight at breeding. The average age for both groups was 416 ± 18 days with an average weight of 325.06 ± 33.11 kg and 376.77 ± 29.74 kg for G1 and G2, respectively. Pelvic measurements collected included height, width, and area. The average pelvic area was significantly different (P < 0.0001) for G1 and G2 with measurements of 162 ± 16.38 cm2 and 174 ± 17.56 cm2, respectively. A significant difference was also observed for pelvic height and width (P < 0.05). The average pelvic height was 14.06 ± 0.93 cm for G1 and 14.41 ± 0.93 cm for G2. The pelvic width was measured with an average for G1 and G2 was 11.47 ± 0.64 cm and 12.05 ± 0.70 cm, respectively. A regression analysis examined the effect of group and age on pelvic area. Heifer age and group were both significant in the model (P < 0.05) with regression coefficients of 0.47 ± 0.07 cm2 /day and 12.42 ± 2.65 cm2, respectively. The adjusted R-squared value was 0.34. A second regression analysis was conducted to examine the pelvic area as a function of group and an adjusted yearling weight. Heifer age and yearling weight were highly correlated, as such, yearling weight was adjusted based on Beef Improvement Federation guidelines to account for animal age. The resulting regression coefficient for adjusted yearling weight was 0.15 cm2/kg (P = 0.005) and 6.56 cm2 (P = 0.076) for the group. The adjusted R-squared value was 0.16. In conclusion, G2 had a significantly larger pelvic area as compared to G1. The regression analyses demonstrated that both age and adjusted yearling weight were associated with pelvic area. As age and adjusted yearling weight increased, pelvic area also tended to increase.