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Effects of Calf Value and Reproductive Management on Optimum Days to First Breeding

Agricultural Research Organization, The Volcani Center, PO Box 6, Bet Dagan 50250, Israel

The effect of days open and days to first breeding on cumulative calf and milk production in the current and following lactation was studied based on annualized yield in 121.627 Israeli-Holstein lactations. Optimum days open for first parity ranged from 110 for low calf value (500 kg milk) to 91 for high calf value (4000 kg milk). Optimum days open for second parity ranged from 91 for low calf value to 40 for high calf value. Expected production as a function of days to first breeding was computed as a function of probability of conception, which was varied from .4 to .6, and estrus detection, which was varied from .5 to .7. Optimum days to first breeding as a function of calf value and reproductive management ranged from 95 to 65 d for first parity and from 77 to less than 40 d for second parity. Optimum days to first breeding was higher with lower calf value and better reproductive management. Expected losses from early first breeding (40 d in milk), as compared with the optimum, ranged up to 780 kg of FCM for first parity cows, while expected losses from late first breeding (120 d in milk) ranged up to 790 kg for second parity cows.

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