Reproductive performance of F1 crossbred dairy cows used for draught: Effect of work and diet supplementation

Forty pregnant crossbred cows (20 Holstein-Friesian X Boran and 20 Simmental X Boran) were assigned to a 2x2 (work X diet) factorial experiment as follows: supplemented-non-working (SNW), supplemented-working (SW), non-supplemented-non-working (NSNW) and non-supplemented-working (NSW). Working cows pulled sledges 100 days/year. Conception and oestrous at fixed times were analysed using linear logistic models. Proportional hazard models were used for analysing `failure' time data such as time to first oestrous or time to conception. Diet supplementation significantly decreased days to first oestrus and days to conception in non-working and working cows. SW cows had similar reproductive performance to NSNW cows. In supplemented cows, work significantly delayed days to conception. However, by 365 days postpartum, conception rate was similar for SNW and SW cows. Body condition at calving significantly affected post-partum reproductive ability of crossbred cows. Work output of supplemented cows may be associated with longer calving intervals. The economic trade-offs between longer calving intervals and work output should be examined in detail