Direct and maternal additive effects and heterosis were estimated using data from straightbred Angus, Brahman, Charolais, Hereford, and four generations of rotational crosses among these breeds. Traits of interest were birth weight, Julian day of birth, average daily gain from birth to weaning, 205-d weight, and weaning weight per cow exposed. Complete data were available on 3,445 calves produced from 4,733 matings. Discrete generations of 4-yr duration were produced from 1970 through 1988. Brahman was included in each rotational crossbreeding system. Genetic effects were estimated by regression. Direct and maternal additive effects of Brahman, Charolais, and Hereford were estimated as deviations from Angus. Direct and maternal heterosis effects were assumed proportional to expected heterozygosity. The Brahman direct additive effect resulted in later-born calves (P < 0.01). Brahman, Charolais, and Hereford direct additive effects increased birth weight, and the Brahman maternal additive effect decreased birth weight compared with Angus (P < 0.05). Charolais direct and maternal additive effects were greater than Angus for average daily gain and 205-d weight (P < 0.01). The Hereford maternal additive effects on average daily gain and 205-d weight were less than those of the other breeds (P < 0.01). Breed combinations including Brahman had greater direct heterosis for birth weight, average daily gain, and 205-d weight than other combinations (P < 0.01). Angus, Charolais, and Hereford direct additive effects on weaning weight per cow exposed were greater than Brahman (P < 0.05). Predicted average daily gain, 205-d weight, and weaning weight per cow exposed were, on average, greater in four-breed rotation systems than in three- and two-breed systems. Among two-breed rotation systems, predicted average daily gain and 205-d weaning weight were greatest for Charolais-Brahman and least for Angus-Hereford. Calves from the Angus-Charolais-Hereford system weighed less at weaning than any other three-breed combination. However, weaning weight per cow exposed from the Angus-Charolais-Hereford system was greatest among three-breed systems. Within three- and four-breed rotation systems, ranges in predicted birth and weaning weights among generations varied by up to 10.0 and 25.2 kg, respectively. The choice of breeds affects performance, and the sequence of their use may affect intergenerational variation in performance.

Birth and weaning data on zebu cattle (Gudali and Wakwa) of north Central Cameroon were analysed. Calf breed, sire and sex had significant effects (P < 0.01 or 0.001) on birth weight while parity and season of birth were not important. Calf breed, sex, season of birth and birth weight had significant effects (P < 0.05 or 0.01 or 0.001) on 8-month weaning weight. Sire and parity had no significant effects (P > 0.05) on weaning weight. Wakwa calves were heavier at birth (24.30 +/- 0.42 versus 22.6 +/- 0.56 kg) and weaning (158.32 +/- 3.46 versus 148.77 +/- 2.88 kg) than Gudali calves. An increase of 1 kg in birth weight led to an increase of 1.27 kg in weaning weight. Calves born at the end of the rainy season were heavier at birth, but were lighter at weaning than those born at the beginning of the rainy season. These results suggest that under extensive low input husbandry conditions calving should be programmed for the end of dry season/early rainy season (breeding during middle to end of the rainy season).

Data from production and financial records from the Wakwa Centre for Animal and Veterinary Research were used to find out whether or not genetic improvement for dairy production is a profitable investment. The herd projection computer program was used to herd-project the performance of 100 Holstein x Gudali crossbred and 100 Gudali heifers over a 10-year period. Despite the high mortality rate of the crosses, their overall improvement over the local Gudali led to a benefit-cost ratio of 4.21. This suggests that genetic improvement of local cattle through crossbreeding for dairy production can be a profitable venture. Crossbred dairy farming is therefore recommended for the dairy industry in Cameroon.