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 production of their dams were used to evaluate breed of dam effects, breed of sire effects, and individual heterosis effects. Hereford and Tarentaise dams were mated to Hereford and Tarentaise sires and calves were born from 1987 to 1991. Calf traits were birth weight, proportion calving difficulty, weaning weight, weaning height, weaning weight:height ratio, and condition score at weaning. Cow traits were milk production four weights during the year, weight changes, height at weaning, condition 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 breed 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 calf weight:cow weight. Least squares means for Hereford and Tarentaise dams, respectively, were 216 and 236 kg for calf weaning weight, 6.2 and 9.3 kg for late milk production, 559 and 507 kg for cow weight at weaning, 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 significant 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 weighted more and had higher levels of condition, whereas Tarentaise dams produced more milk late in lactation and weaned heavier calves.