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Dairy Pipeline: November 2003
Ray L. Nebel
Dairy Extension Coordinator and Reproductive Management Scientist
(540) 231-4432
email: rnebel@vt.edu
Timed AI (TAI) programs are becoming popular because of the frustrations and failures to detect cows in heat. Our research at Virginia Tech over the past 10 years has shown that the average Holstein cow expresses "standing heat" for 7.5 hours with approximately ONE mount per hour. I believe this combined with larger herds and less time and labor to conduct three daily observation sessions has led to estrus detection rates where less than 50% of the cycling cows are being observed in heat in a timely manner. The average days to first service for Virginia DHI herds last month was 98 days which means half of all cows inseminated receive their first service after 100 days in milk. The first advantage and maybe the most important benefit of a TAI program is all cows receive first service within a narrow window of time (usually 6 to 13 days). We have used TAI exclusively at the University Dairy Center over the past 16 months and the average days to first service is presently 78 days or 20 days lower than the average for Virginia DHI herds. Dairy cows inseminated with TAI program usually have a lower conception rate when compared to dairy cows inseminated after an observed estrus. During the past 16 months we have averaged a 30% conception rate with TAI. Our monthly conception rate for cows inseminated with TAI has ranged from 13 to 52%; however, the pregnancy rate (number of eligible cows that become pregnant ever 21 days) has average 20%. Usually the traditional reproductive indices such as services per conception and conception rate are negatively affected when TAI is implemented. The interval from calving to first service and overall pregnancy rate almost always improves when a TAI program is implemented. I believe the bottom line for any reproductive management program to be successful is it must produce pregnant cows in a timely manner. I am convinced that for the majority of herds a properly conducted Timed AI program is the number one option to GET MORE PREGNANT COWS.