MATERNAL FACTORS AND THE PREDICTION OF DYSTOCIA IN BEEF HEIFERS

Stepwise discriminant analysis was used to determine maternal factors associated with dystocia in 564 2-yr-old heifers bred to bulls with be low breed average birth weights. Calf birth weight (n = 556) was consi stently the most significant (P < 0.001) factor correlated (R2 = 0.31) with dystocia. Other significant (P < 0.001) factors were weight at b reeding (n = 376) and calving (n = 559; R2 = 0.11 for both traits). Ot her factors considered were age at breeding (n = 446), pelvic area at breeding (n = 112) and pregnancy evaluation (n = 297), heifer birth we ight (n = 564), gestation length (n = 467) and age at calving (n = 559 ) but none were significant (P > 0.05). Heifers requiring caesarian se ction were heaviest (P < 0.05) at breeding and their calves were heavi est (P < 0.05) at birth. Unassisted heifers were heavier at calving (P < 0.05) than assisted heifers. It was concluded that none of the fact ors examined in this study was a reliable predictor of dystocia in bee f heifers but that heifers should be bred at 75-80% of their expected calving weight to reduce the risk of dystocia.