Genetic assessment of rectal temperature and coat score in Brahman, Angus, and Romosinuano crossbred and straightbred cows and calves under subtropical summer conditions

The objectives of this study were to characterize rectal temperature and coat score under subtropical North American summer conditions for straightbred and crossbred Romosinuano, Brahman, and Angus cattle, to estimate heterosis and breed direct and maternal effects in a subset of those, and to estimate heritability and genetic correlation of these traits. Records of cows (n=612 cows; 1861 total records) and calves (n=1588) from summer days in subtropical Florida, USA, were evaluated using animal models. Records of cows and calves from 2 management groups were analyzed separately. In the first management group, cows were all straightbred as were their calves; most of these cows were dams of cows in the other management group. Cows in that second management group were produced from all possible matings of Romosinuano, Brahman, and Angus bulls and cows; breed groups were 3 straightbred groups and 3 groups of F1 cows (reciprocal crosses combined). Calves of these cows were 3-breed crosses (all F1 cows were mated to bulls of the 3rd breed) and F1 crosses (straightbred cows were bred in approximately equal numbers to bulls of the other 2 breeds). Angus straightbred and crossbred cows and calves had the highest rectal temperature and coat score (subjective score where larger numbers indicated greater quantity of hair on the coat) means in all 4 analyses. In the second management group (straightbred and crossbred cows raising crossbred calves), Romosinuano straightbreds and F1 Romosinuano-Brahman cows had the lowest (P<0.001) rectal temperature and coat score means. Heterosis for rectal temperature was −0.2±0.05 and −0.24±0.05 °C for Romosinuano-Angus and Brahman-Angus, respectively (P<0.001). Heterosis for coat score was −1.4±0.2, −0.9±0.2, and −2±0.2 for Brahman-Angus, Romosinuano-Brahman, and Romosinuano-Angus, respectively (P<0.001). Direct effects of Romosinuano and Brahman reduced rectal temperature and coat score; direct effects of Angus increased both. Estimates of heritability were 0.19±0.03 and 0.27±0.04 for rectal temperature and coat score, respectively. Permanent environmental effects as proportions of phenotypic variance were 0.03±0.02 and 0.17±0.04 for rectal temperature and coat score, respectively. The estimate of genetic correlation of these traits was 0.24±0.09. With respect to these traits, Romosinuano may offer benefits of tropical adaptation at least to the extent of Brahman under Florida summer conditions.