Heterosis, additive maternal and additive direct effects of the Red Poll and Boran breeds of cattle.

Data on 202 calves born, 191 calves weaned and 182 calves at 30 mo of age produced in 1969 from the Boran and Red Poll breeds and their reciprocal crosses were analyzed to estimate heterosis, additive maternal effects and additive direct effects on survival and growth traits from birth to 30 mo of age. The calves were produced in the Ankole District of south-western Uganda as a part of a beef cattle research program designed to provide information to support a commercial ranching development scheme in an area that had been cleared of the tsetse fly. Breed of sire effects were significant for birth and weaning weight, and breed of dam effects were significant for birth, weaning and 12-mo weight. Breed of sire and breed of dam effects that were significant showed the Boran breed to have higher values for all traits except breed of dam effects on birth weight; calves with Red Poll dams were 3.6 kg heavier (P less than .01) at birth than calves with Boran dams. Steers were significantly heavier than heifers at all ages except birth. Young cows (3 and 4 yr old) and old cows (9 yr old and older) produced calves that weighed significantly less at weaning, 12 mo and 18 mo than calves with dams that were 5 through 8 yr old. Heterosis effects were significant for weights at weaning, 12, 18, 24 and 30 mo of age; generally, heterosis effects on weight increased with age. Heterosis effects approached significance for survival from birth to 30 mo. Additive maternal effects were significant for birth weight; crossbred calves with Boran dams weighted 6.0 kg less at birth than crossbred calves with Red Poll dams. There was a reversal of the reciprocal effect between prenatal and postnatal gains; crossbred calves with Boran dams weighed 7.1 kg more at weaning than crossbred calves with Red Poll dams. Examination of additive direct effects showed the Boran breed to be significantly heavier than the Red Poll breed for birth weight and weaning weight. Additive direct effects showed the Boran breed to have generally higher (P greater than .05) values than the Red Poll breed for most other traits analyzed. Differences between straightbreds of the Boran and Red Poll breeds, which reflect differences in additive maternal and additive direct effects combined, significantly favored the Boran breed for weaning weight and 18-mo weight and favored (P less than .05) the Boran breed for all other traits except birth weight. It was concluded that the Red Poll breed had higher values for additive maternal effects for birth weight than the Boran breed in the climatic and nutritive environment in which this experiment was conducted; for most other traits evaluated, the Boran breed generally had higher values for additive maternal and higher values for additive direct effects than the Red Poll breed.