MORPHOLOGIC ASPECTS OF DYSTOCIA IN DAIRY AND DUAL PURPOSE HEIFERS

Abstract

The phenotypic association between ease of calving and a number of, mainly morphologic, dam traits was examined by stepwise discriminant analysis. Body weight, body dimensions and scores for fat covering and muscularity were obtained for 79 Holstein (H), 90 Dutch Red and White (DRW) and 104 Dutch Friesian (DF) heifers at 10 days after calving, Dimensions were body length, height at hips and withers, width and depth of chest, heart girth, hip width and spiral girth. About half of the heifers had data on precalving pelvic dimensions, both internal (height and width of pelvic inlet) and external (width at hips and thurls, pinbone distance, horizontal and vertical distances between hip and thurl, and hip and pinbone). Birth weight of all, and body dimensions of live calves were recorded. Calving ease was scored as 'easy' (no or minor assistance), 'normal' (easy pull) or 'difficult' (hard pull or Caesarean). In addition, forces exerted by a calf puller were recorded in a number of easy, normal and difficult deliveries. Analysis of these forces indicated that classification as 'easy' vs. 'normal' was more influenced by subjectivity or chance than 'normal' vs. 'difficult'. Birth weight and almost all calf dimensions were significantly related to ease of calving. All simple relationships involving dam traits lacked significance in H and DF heifers, except precalving hip width in the latter group. DRW heifers experiencing difficult calving were on average heavier and larger framed. Excluding calf dimensions, birth weight was the first variable to enter into the discriminant functions in all three breed groups. Dam traits contributing to discrimination between calving performance categories were depth of chest in H heifers, heart girth, chest width and pinbone distance in DRW heifers, and pelvic height in DF heifers. The possible significance of these effects is discussed. Key words: Dystocia, discriminant analysis, dam traits, dairy cattle