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• A new procedure to synchronize estrus in dairy heifers is under review by the FDA. Approval should be announced in 2001. It involves the concurrent administration of intravaginal progesterone inserts (CIDRs) and PGF_2a.
• Data submitted to the FDA demonstrated that the procedure synchronized 84 percent of the 122 treated heifers. The conception (number pregnant) number inseminated) and pregnancy (number pregnant) number treated) rates were 54 percent and 45 percent, respectively.

BACKGROUND

Methods to synchronize dairy heifers are needed, particularly now that Syncro-Mate B is no longer available. Although heifers can be administered PGF_2a and bred upon the detection of estrus, use is limited for several reasons. Dairy heifers generally have high fertility rates and are easier to manage for breeding than cows because of the absence of milking. However, they are often neglected.

EXPERIMENTAL PROCEDURE

Illinois was included in a multi-location study submitted to FDA for approval of the estrus synchronization procedure that includes the intravaginal progesterone insert and PGF_2a. Other locations included Florida, Missouri, and New York. The study included two groups: Group 1-PGF_2a and Group 2B involved:

• the administration of an intravaginal progesterone insert (CIDR) for seven days, and
• an injection of PGF_2a (25 mg of Lutalyse⁷) one day before insert removal.

After the time of insert removal all females were observed for estrus and bred via the A.M./P.M. rule upon the detection of estrus. Estrus detection began the day after the time of insert removal and continued for 31 days. Pregnancy was determined via transrectal ultrasonography. Intravaginal progesterone insert loss rate was 5 percent.

RESULTS

Table 1. Brief summary of the results included in the FDA submission and an article submitted to the Journal of Animal Science.

Synchronization Rate: estrus during the first three days of the breeding season

Conception Rate: number pregnant ÷ number inseminated

Pregnancy Rate: number pregnant ÷ number treated

Overall, inclusion of the intravaginal progesterone insert increased the number of heifers in estrus and the number of heifers conceiving during the first three days of the breeding season. Although, the PGF_2a was administered one day before insert removal, subsequent research has demonstrated that treatment on the day of insert removal will yield similar results. Therefore, this procedure has utility in managing reproduction in dairy heifers. The procedure is expected to be available sometime during 2001 and it will be distributed by Upjohn Animal Health.

CONCLUSION

Use of the intravaginal progesterone insert (CIDR) along with PGF_2a effectively synchronizes estrus in dairy heifers. It is expected to be available in 2001; however, approval for use in lactating cows is not being sought at this time. Approval for use is lactating cows is expected to be sought after approval is acquired for its use in heifers. During 2001 there will be procedures to synchronize estrus in dairy heifers: PGF_2a, MGA and PGF_2a (discussed in another article within this publication), and the concurrent use of CIDRs and PGF_2a. Producers should obtain the advantages of AI and reduce the reliance on estrus detection as heifers are an easy to bred female.