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Progestin and Prostaglandin for Estrous Synchronization in Beef Heifers^1,2,

University of Nebraska West Central Research and Extension Center, North Platte 69101

Abstract

Seventy-eight Simmental-Angus-Hereford crossbred yearling heifers, in 1983, and 99 similar heifers, in 1984, were used to compare two estrous synchrony regimens. One treatment group (SMB) was synchronized using the commercially available Syncro-Mate-B procedure, which involved placing a norgestomet implant in the ear for 9 d and giving an injection of norgestomet and estradiol valerate at the time of implantation. A second group (PR + PG) was given a norgestomet implant (PR) for 7 d and a 5-mg injection of alfaprostol (PG) at implant removal. Percentage of heifers cycling during the synchronization period and percent conceiving in 5 d or 30 d were not different (P>.10) due to treatment. The interval from implant removal to onset of behavioral estrus was shorter (P<.01) for the heifers treated with SMB than for the heifers treated with PR + PG (42.8 vs 58.0 h). The group treated with SMB had a more uniform synchrony of estrus than the group treated with PR + PG. The effect of day of the estrous cycle at implantation on hours to estrus after implant removal was determined by a regression analysis, which showed a linear response for the SMB group with a slope of .78 (P=.09); the PR + PG group regression was cubic (P<.01); this also indicated a more uniform response by the SMB group. These results indicate that the combination of norgestomet and alfaprostol produced more variation in interval from treatment to estrus than the Syncro-Mate-B procedure. However, conception rates were not different when inseminations were performed following an estrus that was detected by visual observation.

¹ Published as Paper No. 7919 Journal Ser., Nebraska Agr. Exp. Sta.

² Appreciation is expressed to Hoffmann-LaRoche Inc., Nutley, NJ for providing products and partial funding of study.

³ Dept. of Anim. Sci., Univ. of Missouri, Columbia 65211.