286 Effects of Presynchronization with Prostaglandin F2α and a Progestin, and Delayed Insemination on Pregnancy Rates with Sexed Semen in Replacement Beef Heifers

Abstract To determine effects of presynchronization and delayed fixed-time artificial insemination (TAI) on pregnancy rates (PR/AI) with sexed semen, 1,844 beef heifers were enrolled in a completely randomized design at 12 locations. Within location, randomly assigned to one five treatments: 1 2), administered prostaglandin F2α (PGF) day -7, gonadotropin-releasing hormone (GnRH) CIDR insert 0, PGF removal 7, another injection GnRH TAI 72 hours later conventional (CTRL72-CNV) or semen (CTRL72-SEX); 3 4), treated the same as CTRL72 but received -7 administration 60 (CIDR60-CNV) (CIDR60-SEX); 5), CIDR60 had (CIDR72-SEX). Estrus expression between 7 did not differ (P=0.92) CIDR72 was greater (P< 0.001) compared heifers. Among treatments, PR/AI differed (P≤0.003) CTRL72-CNV CIDR60-CNV than CIDR60-SEX CIDR72-SEX Furthermore, CTRL72-SEX when only tended (P=0.09) No differences (P=0.33) determined (P=0.22). In conclusion, no presynchronized those inseminated either semen. Therefore, use for an additional days beneficial Additionally, delaying after both has negative impact PR/AI.