In three trials conducted in 3 successive years, Africander, Brahman, Tswana, Tuli and crossbred cattle were injected intramuscularly with 500 jug of cloprostenol on two occasions 11 days apart to synchronize oestrus. The cattle were inseminated 72 and 96 h after the second injection. Controls of the same breeds were exposed to natural service for a period of 22 days. In all trials the conception rate to natural service was significantly higher (P<0-0l). Conception rates to both breeding methods were highest in Tuli and crossbred cattle and lowest in the Africander and Brahman. Nonlactating cows showed higher fertility than suckling cows and maiden heifers. Vasectomized bulls used in one trial were shown to be useful in the selection of breeding cows suitable for oestrus synchronization. Further studies are justified to maximize the benefits of a potentially valuable method of breeding beef cattle in ranching conditions.

In a trial to evaluate the growth of crossbred calves under semi-arid ranch conditions in Botswana, pure Tswana and crossbred beef cows were inseminated with Beefalo and Italian semen or mated naturally with Brahman, Simmental or Tswana bulls. The 424 calves produced were weighed at birth and at monthly intervals t o 18 months of age.Beefalo crossbred calves were significantly lighter at birth than all other calves (P<0·05). At weaning (7 months) Brahman-sired calves were significantly heavier than Tswana calves, but no heavier than the other breed types. At 18 months of age Brahman, Italian and Simmental crosses were all significantly heavier than Tswana calves (P<0·05), but there was no significant difference between Beefalo crossbred and pure Tswana calves.These results indicated that the Beefalo cross had no advantage over the indigenous Tswana breed and more-conventional breeds were superior when crossed with the Tswana.