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Synchronized Estrus and Subsequent Conception in Dairy Heifers Treated with Prostaglandin F₂. I. Influence of Stage of Cycle at Treatment^1,2,

The Pennsylvania State University, University Park 16802 and and Milton Hershey School Farms, Hershey, PA 17033

Abstract

When prostaglandin F₂ (PGF₂) was injected (im) at three different stages of the cycle, estrus was synchronized within an 80-h period in a progressively, but nonsignificantly, higher percentage of heifers with each advancing stage: 86.0% at d 7, 90.0% at d 11 and 98.0% at d 15. Estrus was exhibited within a 48-h period for heifers treated on d 7, but extended over a 72-h period for heifers treated on either d 11 or 15. Stage of cycle when PGF₂ was injected not only influenced the degree of estrous synchrony, but also influenced (P<.001) the time of estrous onsets. Within the 24-h interval from 32 to 56 h postinjection, the percentage of heifers exhibiting estrus from treatment on d 7, 11 or 15 varied widely: 88.4, 13.3 and 73.5, respectively. Induction of estrus was complete, or nearly so, by 72 h postinjection for heifers treated during the early (d 7 = 100.0%) or late (d 15 = 95.5%) stage of the cycle, but reached only midpoint for midcycle injections (d 11 = 48.9%), with the remaining one-half (51.1%) occurring 72 to 104 h later. Pregnancies arising from the first through the fifth services among the 150 PGF₂-treated heifers were as follows: 76.0, 10.0, 6.7, 4.0 and .7%, plus failure of pregnancy in 2.7%. These percentages were not different (P>.50) from those among the 50 control heifers.

¹ Authorized for publication as Paper No. 6488 in the Journal series of the Pennsylvania Agr. Exp. Sta.

² This research was conducted as part of the Pennysyvania contrubiting project to the NE-72 Regional Project, 'Development of the Controlled Ovulation and Pregnancy Program in Cattle.'

³ Dairy Breeding Research Center, Dept. of Dairy and Anim. Sci.

⁴ Milton Hershey School Farms.

⁵ The authors express their gratitute to the following: Northeastern Breeders Assoc, Tunkhannock, PA for the grant-in-aid; Dr. J. W. Lauderdale, the Up-john Co., Kalamazoo, MI, for the generous supply of prostaglandin F₂ (Lutalyse); Dr. J. L. Rosenberger for statistical counsel and assistance; James Norris and Fred Speicher for experimental insemination of the heifers, and Scott Seibert, Cecil Crider and Dennis Price for valuable technical assistance.

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