Calf crop born, calf crop weaned, calf birth weight, calf weaning weight, and cow weight at weaning were evaluated from 1996 to 2009 in Brahman (B) and Hereford (H) straightbred and crossbred cows (n = 1,515). The objective of these analyses was to estimate heterosis for F1 and F2 females for these reproductive and maternal traits. Breed groups included B, H, F1 Hereford-sired (HB) and Brahman-sired (BH) cows (n = 114 purebreds, 55 F1, 52 F2). Second generation breed groups included cows sired by HB and out of HB dams (F2HB) and BH dams (HBxBH); and cows sired by BH and out of HB dams (BHxHB) and BH dams (F2BH). Least squares means were calculated for calf crop born, calf crop weaned, and calf birth and weaning weights, using numerous different models, where the trait was the dependent variable. Previous research and these preliminary analyses showed that the effects of year and cow age are real as is their interaction each other and with breed type. In each attempted model designed to remove these effects, different breed groups received excessive adjustments, rendering the resultant heterosis estimates inappropriate. To more clearly assess differences, presentation and visual evaluation of unadjusted means were conducted. The model for mature cow weight (cows at 6 years of age) included breed group as fixed effects and cow within breed group and year as random effects. F2 cows appeared to retain approximately 39% of F1 heterosis for calf crop born and approximately 50% for calf crop weaned. HB x BH cows delivered the lightest calves at 33.9 (4.74) kg and F2BH had the heaviest calves at birth at 36.6 (5.37) kg. BH cows weaned the heaviest calves at 240.9 (38.1) kg and F2BH cows weaned the lightest calves at 208.4 (31.9) kg. Sire breed of calf and age of cow appear to be important factors regarding weight traits. Retained heterosis for cow weight at weaning was higher than expected at 73%. Sire breed group differences (HB vs. BH) for these traits in F2 cows may merit further investigation.

Reproductive and weight traits were analyzed for Angus (A), Brahman (B), Hereford (H), and Nellore (N) straightbred cows; F1 NA cows; 3/8N 5/8A cows and quarter blood composite cows (BANH) of the four straightbreds in Central Texas. Heterosis was estimated for calf crop born (CCB), calf crop weaned (CCW), and calf survival (CS) by linear contrasts within cow breed groups. F1 NA cows expressed heterosis (P < 0.0001) for CCB (0.22) and CCW (0.20). Except for the 3/8N 5/8Ac cows, which resulted from the mating of NA bulls to 3/4A 1/4N cows, all of the crossbred cow breed types expressed significant heterosis (P < 0.05) when compared to the weighted average of the parental purebreds for CCB. BANHc cows that were the result of mating NA bulls to HB cows expressed heterosis for CCB (0.35) (P < 0.001) and CCW (0.29) (P < 0.05). The 3/8N 5/8Aa females produced by mating 3/4N 1/4A bulls to NA cows expressed heterosis (P < 0.0001) for CCW (0.20). Heterosis for calf survival was near zero for all breed types, but only two breed types of 3/8N 5/8A cows were significantly greater than the weighted average of the parental purebreds. Heterosis for birth weight (BWT) and weaning weight (WWT) was also analyzed by linear contrasts within cow breed groups. The BANHb and BANHc cows produced from mating NA bulls to BH and HB F1 cows, respectively, expressed heterosis for BWT (2.89 + 0.79 (P < 0.001) and 3.38 + 1.51 (P < 0.05)). All cow breed types expressed significant heterosis (P < 0.05) for WWT. The BANH2 cows resulting from the mating of NA bulls to F2 HB or BH cows expressed heterosis (P < 0.0001) for WWT (52.01 kg + 9.88).