Despite the widespread adoption of hormonal synchronization protocols that allow for timed artificial insemination (AI), detection of oestrus plays an important role in the reproductive management program on most dairies in the U.S. Increased physicalactivity is a secondary sign of oestrus in dairy cattle, and a new generation of electronic systems that continuously monitor physical activity to predict timing of AI have been developed and marketed to the dairy industry. A variety of management and physiologic challenges inhibit detection of behavioral oestrus on farms, but the prevalence of anouvular cows near the end of the voluntary waiting period is particularly problematic. Only 70% of lactating Holstein cows were detected in oestrus when usingan activity monitoring system, with the remaining 20% of cows classified as anovular and 10% ovulating without showing signs of activity. Mean time of AI in relation to ovulation based on the activity monitoring system was acceptable for most of the cows with increased activity; however, variability in the duration of oestrus and timing of AI in relation to ovulation could result in poor pregnancy outcomes in some cows. Use of a Presynch-Ovsynch protocol for submission of cows for first AI has been widely adopted by dairies in the U.S., and a combined approach in which AI based on activity is followed by submission of cows not detected with activity to timed AI after synchronization of ovulation may be an effective strategy for submission of cows to first AI. Based on a field trial on a large commercial dairy in the U.S., the activity monitoring system detected 70% of cows with increased activity after the second PGF2a injection of a Presynch-Ovsynch protocol; however, cows inseminated to increased activity had fewer pregnancies per artificial insemination (P/AI) compared to cows with increased activity after the second PGF2a injection that received timed AI after completing the Presynch-Ovsynch protocol. Based on an economic model comparing reproductive management programs with varying levels of AI to oestrus versus timed AI, the rate of oestrous detection and the P/AI to inseminations based on AI to detected oestrus versus timed AI affected the decision to inseminate based on activity versus timed AI. In conclusion, an activity monitoring system detected increased activity in about 70% of lactating Holstein cows on a large commercial dairy in the U.S.; however, synchronization of ovulation and timed AI was beneficial to inseminate cows not detected with increased activity by the activity monitoring system.
展开▼
