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Dairy Pipeline: March 2004
Ray L. Nebel
Extension Dairy Scientist,
Reproductive Management
(540) 231-4432
email: rnebel@vt.edu
Timed AI programs are becoming popular because herds with poor heat detection rates can achieve lower days to first service and higher pregnancy rates (PR) in contrast to when cows are inseminated via non-synchronized observed estrus. Synchronization of estrus behavior, through pharmacological control, has been used to improve reproductive efficiency since the late 1970's. Methods of synchronizing estrus were originally devised to decrease the time spent detecting estrus; however, timed AI programs, especially those that eliminate heat detection, are now being used for convenience and efficiency in reproductive management. To effectively influence reproductive performance and impact the income of the herd, a timed AI should be based on a methodical approach for the entire herd, rather than the individual cows. Approximately 50% of the profit per lactation is generated in the first 100 days of lactation. During this period the return per feed dollar is usually three to one, in contrast to late lactation when it is approximately one to one. A goal of the reproductive management program should be to have cows spend as much of their life in the early phase of lactation as possible. Thus, it is critical that the reproductive management program focus on getting a large percentage of the cows pregnant quickly after the voluntary waiting period, so that the majority of the cows will spend a sufficient proportion of their lives in early lactation. Basic research identified the existence of follicular waves and allowed for the development of programs that synchronize both luteal regression and follicular maturation, leading to ovulation. OvSynch developed in the mid-90's allowed for the first timed AI program that obtained CR similar to those of cows inseminated following detected estrus. Modifications of the OvSynch program to maximize cows between day 5 and 12 in their estrous cycle (PreSynch) have shown a further enhancement in CR to timed AI. For best results, visual heat detection should be conducted following synchronization because cows will stay synchronized with approximately 60% of the cows initially synchronized returning to cycle 18 to 24 days following AI. Herds that have a 70 day voluntary waiting period and a heat detection program that yields an average PR of 22% are estimated to obtain an average days open of approximately 115 days or a 13-month calving interval. Therefore, it is not economically justified to use a timed AI program if the visual heat detection program produces an average PR of 22% or higher, with labor costs for heat detection of approximately $10 per day.