A comparison of productivity over a 4-year period from indigenous type beef cattle under two production systems in Botswana is reported. The two systems are: the traditional system on unenclosed communal grazing (cattle post) and ranching within fenced paddocks. Calving percentages, 7-month old calf weight, calf mortality and post-weaning growth to 18 months of age under cattle post conditions were 46.4 per cent, 122.5 kg, 10.2 percent and 88.5 kg respectively. Corresponding figures for cattle on the fenced ranches were 74.0 per cent, 177.4 kg, 8.5 per cent and 105.8 kg. These results indicate overall productivity estimates of 51 and 120 kg of weaner calf per cow per year and 86 and 188 kg of 18-month old calf per cow per year for the cattle post and fenced ranch respectively.

The three indigenous beef cattle breeds in Botswana, the Tswana, Africander and Tuli, were evaluated for reproductive performance, viability and growth. Over 3 yr the calving percentages of 1389 Africander cows, 305 Tswanas and 357 Tulis were 64-5, 70-6 and 85 respectively. These differences were significant (P < 0-05). Mortality of the Africander calves was higher to 2 yr of age, being 11 % compared with 7-5% for Tswana calves and 7-4% for Tulis. The 18 mo weight of 219 Tuli cattle was 284 kg, and of 454 Tswanas 279 kg, both superior to the 270 kg for the 786 Africanders. Productivity estimates combining these three traits demonstrate the value of the Tuli breed for Botswana conditions. Comparisons of the crossbreds produced by the use of Simmental, Brahman, Bonsmara and Tuli sires on Tswana cows showed an advantage in growth to 18 mo through crossbreeding. The 18 mo weights of Simmental and Brahman crosses at 324 and 304 kg respectively were significantly different, and superior to the weight of pure Tswana at 279 kg. Bonsmara and Tuli crosses at 294 and 290 kg also showed a significant increase over the pure Tswana. The use of the Simmental is now recommended for better management conditions, with Brahman crossbreeding on a wider scale.

SUMMARYEffects on cow reproductive performance, of cow age, parous state, body weight and body-weight change over the breeding season were examined using 6490 annual records from indigenous cows in Botswana.Calving percentage rose from 69% at 2·5 yr of age to a maximum of 82% at 6 to 7 yr and declined in cows over 8 yr of age. Heifers and previously non-parous cows had a calving percentage of 85%; 8, 18 and 30% higher respectively than parous cows that had calved at the beginning, middle and end of the previous calving season. Cows weighing less than 300 kg at the beginning of the mating season achieved a 50% calving. This rose steadily to 85% as body weight increased to 430 kg.Cows that lost weight over the mating period achieved a 67% calving, while gains of 20 kg raised this to 76%. Increased weight gains thereafter had little effect on calving percentage. In all cases, as percentages increased, days to conception decreased in a similar manner.Under these range conditions in Botswana, animals least likely to achieve high calving percentages were young cows; cows which calved previously at the end or middle of the calving season; cows less than 310 kg in weight; and cows gaining less than 20 kg body weight during the mating season.

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.

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