Use of timed AI programs to optimize reproductive efficiency in dairy heifers
Rearing replacement heifers is a vital component of success in the dairy industry. It is also a demanding process that involves management of colostrum, animal husbandry and welfare, protocols for disease control, and nutrition to promote adequate growth rates. Although reproduction accounts for only 2% of heifer rearing costs, reproductive performance plays a major role on the economics of growing heifers. Reducing age at first calving minimizes non-productive days when daily maintenance costs range between $2.00 and $3.00 per heifer. In fact, heifers that calve for the first time between 23 and 24 months of age require 5% less input compared with herd mates that calve at 25 months of age. On the other hand, calving before 23 months of age led to reduced milk yield and smaller reproductive efficiency in first lactation cows.
The proportion of heifers that are inseminated and become pregnant soon after being moved to breeding groups dictates age at first calving. Although protocols for synchronization of ovulation and timed artificial insemination (AI) allow producers to breed all heifers at an optimal age, less than 4% of U.S. herds use such programs to manage reproduction in youngstock. One of the main reasons for the reduced adoption of timed AI has been the perception that fertility is not an issue in dairy heifers and there is little room for improvement. Another major impediment was the lack of synchronization protocols that were optimized for use in dairy heifers. A summary of research published before 2010 indicated that pregnancy per AI (P/AI, commonly referred to as conception rate) in heifers receiving timed AI was smaller compared with counterparts inseminated following detected estrus (38.8 vs. 52.0%). After a series of studies conducted to tailor synchronization protocols to the unique aspects of heifer reproductive physiology, researchers at the University of Florida developed a timed AI program that results in P/AI around 60%; thus, comparable to that observed in heifers bred on estrus (Figure 1).
Lima et al., 2011
Figure 1. Timed AI program optimized for dairy heifers. P4 = intravaginal insert containing progesterone
More recently, a study performed in California dairies showed that the incorporation of timed AI to the reproductive management of dairy heifers also reduces raising costs. The two programs compared were (1) estrus detection aided by prostaglandin-F2α (PGF2α) injections every 14 days for non-inseminated heifers and (2) one-timed AI using the protocol depicted in Figure 1 followed by estrus detection. The two groups were allowed four breeding cycles to become pregnant (i.e. 84 days since heifers were moved to the breeding pens). By design, all heifers subjected to timed AI were inseminated for the first time within two days of becoming eligible for breeding whereas the heifers subjected solely to estrus detection were inseminated on average 10 days after being moved to breeding pens. Pregnancy per AI to first service was similar for heifers subjected to timed AI and those inseminated in estrus (62.8 vs. 58.3%, respectively). In addition to shortening days to first AI, return to estrus in heifers subjected to timed AI was also concentrated around 22 days after the previous insemination. The combination of shorter time to first and second AI and elevated P/AI resulted in greater pregnancy rate in heifers subjected to timed AI. A final finding from the study was that P/AI in heifers bred to sex-sorted semen was greater for timed AI compared with estrus detection (54.8 vs. 31.6%).
Greater costs with hormonal treatments associated with the synchronization protocol were offset by improvements in reproductive performance, which led to a reduction in total rearing costs. The total costs per heifer and per pregnancy were $9.43 and $17.00 less when timed AI was implemented. Most of the difference between rearing costs for heifers subjected to timed AI or estrus detection comes from reduced time to pregnancy and smaller inputs associated with feeding non-lactating animals – a decrease of $21.68 per heifer over the experimental period.
The use of timed AI in dairy heifers has the potential to improve pregnancy rate; thus, reducing time to pregnancy and rearing costs associated with feeding. Nevertheless, this economic benefit relies on elevated P/AI in response to synchronization protocols. Besides promoting animal health and adequate nutrition, dairy producers and heifer growers must ensure that poor facility design and training of herd personnel will not limit compliance to the timed AI program.
Lima, F.S., H. Ayres, M.G. Favoreto, R.S. Bisinotto, L.F. Greco, E.S. Ribeiro, P.S. Baruselli, C.A. Risco, W.W. Thatcher, and J.E.P Santos. 2011. Effects of gonadotropin-releasing hormone at initiation of the 5-d timed artificial insemination (AI) program and timing of induction of ovulation relative to AI on ovarian dynamics and fertility of dairy heifers. J. Dairy Sci. 94:4997–5004.