TARENTAISE AND HEREFORD BREED EFFECTS ON COW AND CALF TRAITS AND ESTIMATES OF INDIVIDUAL HETEROSIS

Preweaning and weaning records on 457 calves and weights and milk prod uction of their dams were used to evaluate breed of dam effects, breed of sire effects, and individual heterosis effects, Hereford and Taren taise darns were mated to Hereford and Tarentaise sires and calves wer e born from 1987 to 1991. Calf traits were birth weight, proportion ca lving difficulty, weaning weight, weaning height, weaning weight:heigh t ratio, and condition score at weaning. Cow traits were milk producti on, four weights during the year, weight changes, height at weaning, c ondition score, ratio of calf weight:cow weight, proportion calved and weaned, and calf weaning weight per cow exposed to breeding. Breed of sire was nonsignificant for all traits except calf hip height, but br eed of dam was significant for calf weaning weight and condition score , late milk production, change in milk production, and the cow traits of all weights, condition score, weight:height ratio, and ratio of cal f weight:cow weight. Least squares means for Hereford and Tarentaise d ams, respectively, were 216 and 236 kg for calf weaning weight, 6.2 an d 9.3 kg for late milk production, 559 and 507 kg for cow weight at we aning, 6.0 and 4.9 for cow condition score, and .39 and .47 for ratio of calf weight at weaning:cow weight at weaning. Heterosis was signifi cant for birth weight (1.05 kg, 3%, P = .01), weaning weight (11.0 kg, 5%, P = .01), and condition score (.13, 2%, P = .06). Thus, Hereford dams weighed more and had higher levels of condition, whereas Tarentai se dams produced more milk late in lactation and weaned heavier calves .