Effects of breed and feed supplementation on the fertility of cows developed for milk production in Zimbabwe

Forty‐six indigenous Sanga‐type (Nkone and Tuli breeds) cows and 46 crossbred (Nkone x Jersey and Tuli x Jersey) cows were randomly allocated to four treatment combinations in a 2 x 2 factorial arrangement with two breeds and two dietary levels, a control diet and a diet supplemented with dairy meal containing 14 per cent crude protein at the rate of 2 kg per cow per day. The progesterone concentration was measured in milk samples taken three times a week from 10 days postpartum for up to 200 days, and the cows' bodyweights and body condition scores were recorded fortnightly. The pregnancy rate in the crossbred cows was significantly higher (P<0·05) than in the indigenous cows, and the assumed pregnancy loss rate 30 days after conception was significantly higher (P<0·05) in the indigenous cows than in the crossbred cows. The supplemented crossbred cows had a lower pregnancy loss rate than the supplemented indigenous cows (P<0·05). All the supplemented indigenous cows that lost pregnancies were in their first parity, whereas all the crossbred cows that lost pregnancies were multiparous and were not supplemented. The indigenous cows weighed significantly more (P<0·05) than the crossbred cows irrespective of diet, and the supplemented cows of both breeds weighed more (P<0·05) than the control cows. The supplemented indigenous cows had significantly higher (P<0·05) body condition scores than the control cows. The mean dairy milk yield of all the breeds was generally low but significantly higher (P<0·05) in the crossbred than in the indigenous cows.