Factors influencing reproductive performance and calf and dam live weights were examined for two indigenous breeds, Angoni and Barotse, and an introduced breed, Boran, under ranching conditions in Zambia.Over 5 years, 675 Angoni, 731 Barotse and 815 Boran records gave calving percentages of 82·5, 78·1 and 75·4 respectively. Year was an important influence on calving and weaning percentages in all breeds; age of dam had little effect and status at mating was only important in the Angoni breed, in which lactating dams produced more calves than dry dams.Mean calf weaning weights were 147·3, 167·0 and 169·5 kg for the Angoni, Barotse and Boran dam breeds respectively. Hereford, Friesian and Boran bulls sired heavier progeny than Angoni and Barotse. Dam age and status did not influence calf weights, which were positively correlated with dam weights and negatively correlated with dam weight change during lactation.Dam live weights at the beginning of the breeding season were 313, 357 and 348 kg for the Angoni, Barotse and Boran breeds respectively. Angoni and Boran dams reached maximum live weight at 7 years and Barotses at 9 years. Subsequent calving rate was not influenced by live weight at the beginning of the breeding season nor, in lactating dams, by live-weight change between the autumn peak and mid breeding season.

Estimates of dam reproductive performance are reported for purebred Africander, Angoni, Barotse and Boran dams, and the reciprocal crossbreds of the latter three breeds, under ranching conditions in Zambia.Mean performances based on a maximum of 1996 records collected over six parities were: calving rate, 65-6%; weaning rate, 62-8%; calf birth weight, 26-6kg; calf weaning weight, 163-6kg; and dam live weight at weaning, 363 0 kg.Purebred Africander and Barotse dams had significantly poorer calving rates, 542 and 57-6% respectively, than the purebred dams of the Angoni and Boran breeds, 69 1 and 66 0% respectively. Reciprocal crossbred dams of the latter two breeds had the highest calving rates, 71-2 and 744%. Heterosis estimates for calving rate were 0-8% for Angoni/Barotse crosses, 7-8% for Angoni/Boran crosses and 10-3% for Barotse/Boran crosses and, for weaning rate, 3-7, 6-7 and 11 5% respectively. There were no differences between reciprocal crossbred dams for calving and weaning percentages. The mortality rate of calves born to crossbred dams was 4 0 % and that of the calves born to purebred dams of the same breeds 4-7 %. Dam status at mating had an important effect on fertility with the calving rate of dams dry at mating, 89-1 %, contrasting with a rate of 39-8% for those dams that were lactating at mating and that had calved late in the season.There were large differences between breeds for calf weights but heterosis estimates were small and nonsignificant. There were no differences between the progeny weights of reciprocal crossbred dams. Sex, date and period of birth, and dam status had significant effects on calf weights.Africander dams had the heaviest, and Angoni dams the lightest, live weights at weaning, 421 1 and 320-7 kg respectively. Heterosis estimates for dam live weights were small and non-significant, and reciprocal crossbred differences were unimportant. Dams which lost most live weight during the dry season, that had extremely light live weights at the beginning of the breeding season or that gained little weight during the breeding season had significantly poorer fertility than other dams.Overall estimates of heritability derived by dam/daughter regression were 0-20 for calving percentage, 0-76 for calf birth weight and 0-72 for calf weaning weight.

Live weights from birth to 3·5 years are reported for beef cattle reared under ranching conditions in Zambia. The 809 cattle were purebred Africanders, Angonis, Barotses and Borans and the reciprocal crossbreds of the latter three breeds born in 2 years. All animals born in the 1st year and half the males born in the 2nd year grazed natural grassland. The remaining males and all females born in the 2nd year received, in addition, dry season supplementary feed from 1·5 years of age.The interaction of genotype with year-of-birth was important but not the interactions of genotype with management or sex. Purebred progeny of the introduced Africander breed were heavier than the progeny of the indigenous Angoni and Barotse breeds in both year-of-birth groups, but only heavier than progeny of the introduced Boran breed in the first group. On average, the Africander progeny had live-weight advantages of about 16% and 10%, and the Boran progeny advantages of about 12·5% and 5·5% over the purebred Angoni and Barotse progeny respectively. Heterosis estimates tended to increase with age, reaching levels of about 5 to 6% in the Barotse/Boran crosses at and after 1·5 years. Heterosis was not shown by the other crosses. The Barotse and Boran breeds had similar maternal effects which were superior to those of the Angoni breed.

Carcass characters for 365 male castrate cattle of the Africander, Angoni, Barotse and Boran breeds, and the reciprocal crossbreds of the latter three breeds, are reported. In each of the two year-of-birth groups, different slaughter-age/management regimes were used. For all carcass characters, except those related to size, the two sanga breeds, Africander and Barotse, were very similar, as were the two zebu breeds, Angoni and Boran. The introduced breeds, Africander and Boran, which had similar carcass weights, had heavier carcasses (+18 kg, +10%) than the indigenous Barotse and Angoni breeds.The sanga breed carcasses had less fat cover than those of the zebu breeds. Maternal effects were not important for carcass characters and the Angoni/Barotse and Angoni/Boran crosses showed no heterosis. In the Barotse/Boran crosses, slaughter and carcass weights and eyemuscle area gave between 8% and 9·5% heterosis, and the linear carcass measurements between 2% and 3%.It was concluded from the management comparisons that there was no economic advantage in delaying slaughter to the later of the two ages compared in the two year-of-birth groups.

Seven hundred and fifty purebred Angoni, Barotse and Boran cattle and their crosses sired by Friesian and Hereford bulls were compared for live-weight and carcass characters in Zambia. The cattle were born between September and December in three consecutive years and were reared on unimproved veld. In the first year all females and a random half of the males received supplementary feed in winter and the males were slaughtered at 2-5 years of age. The remaining males received the same total amount of winter supplementary feed prior to slaughter at 3-0 years of age. The males born in the second year were pen fed for a period prior to slaughter at 3-0 years of age. Males born in the third year were slaughtered at 3-5 years of age and received no supplementary feed.Genotype differences were important at all live weights and there were year of birth x genotype interactions at the 0-5, 1-0 and 1-5 year weights and a genotype x feed treatment interaction at the 2'0 year weight. Boran purebreds were heavier than the Angoni and Barotse purebreds; at 3-0 years the differences were +42-3 kg ( + 12-9%) and + 25-2 kg (+ 7-7 %) respectively. Cross-breds had heavier live weights than their corresponding purebreds with Boran crosses consistently heavier than the Angoni and Barotse crosses. The Friesian and Hereford sired Boran cross-breds were + 51-0 kg (+13-5 %) and + 43-0 kg (+ 11-6 %) heavier respectively than the purebred Borans at 3-0 years of age.There were large differences between the genotypes for all carcass characters with Borans having heavier carcasses than the Angonis and Barotses by + 20-3 kg (+10-6 %) and +19-1 kg ( + 10-0%) respectively. The average carcass weight advantages of Friesian and Hereford crosses with the Angoni, Barotse and Boran breeds over the corresponding purebreds were +40-3 kg ( +19-0%), +33-6 kg ( + 16-2%) and +31-0 kg ( + 14-0%) respectively. There were few important carcass differences between the corresponding Friesian and Hereford crosses.The mortality rate during the experiment was 8-2% with only small differences between genotypes.The interactions found in the experiment indicated that breed comparisons should be conducted over a number of years and at various management levels. For growth and carcass production under the conditions of the experiment the use of exotic crossbreds is clearly advantageous. reliable estimates of breed performance and compansons among breeds which would provide the Genetic improvement can be expected to play a basis for genetic improvement are seldom available, part in increasing the efficiency of cattle production In Zambia for example, published estimates are even in the absence of concurrent improvements limited to a study of the indigenous Angoni in management. Although these conditions often (Walker, 1964) and a comparison of the Angoni prevail in the developing countries of Africa, with exotic breeds for some reproductive charac-