Reproductive Performance of Friesian-Holstein Cows at Sebele Research Station in South Eastern Botswana

Retrospective data from Sebele Dairy Farm were analysed for reproductive performance of Friesian/Holstein cows. Three hundred records from 1989 to 1995 were used. The herd was zero grazed and the data was analysed for age at first calving (AFC), calf birth weights (BW), calving interval (CI), days open (DO), calving rate (CR), reproductive wastage (RW) and calving difficulty (CD); dystocia, afterbirth retention and misrepresentation of foetus) and calving weights (CW). The effects of year of calving (YOC) and year of birth (YOB) were tested. The year of calving affected age at first calving (P 0.05) whereby in 1989/90 and 1990/91 cows were younger than the rest of the years. Calving weight at first calving was significantly affected (P 0.01) by year of calving. YOC had an effect (P 0.05) on both calving interval and days open. CW and CR were significantly affected (P 0.001 and more) by the year of calving. Reproduc-tive wastage tended (P=0.065) to be affected by YOC while no effect (P 0.05) was observed for BW and CD. The year of birth of cows (YOB) had an effect (P 0.05) on age at first calving and it also significantly affected (P 0.01) CW of first calving heifers. Heifers born in the 1980’s had lower live weight at calving than those born in the 1990’s. Age categories (1=20–39 months; 2=40–69 months and 3= 70 months) tended (P=0.062) to influence the birth weights of calves. As cows’ age increased, birth weights of their calves decreased. However, age category did not affect (P 0.05) calving interval or days open. Male calves were heavier (P 0.05) at birth than females (38.7±1.3 kg vs. 36.8±0.7 kg). CW was lower for heifers than for cows and represented 84% of the cows’ weights. Heifers had higher (P 0.01) CR than cows (100 vs. 64.9%), however RW was higher (P 0.01) for heifers than cows (25.0 vs. 11.0%). RW was significantly correlated with birth difficulty (r=0.50; P 0.001). It seems that a low temperaturehumidity index in the month of conception resulted in higher CR nine months later. It is recommended that when cows are zero grazed, feed quality should be assured by nutrient balancing and should not affect performance between years.