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

Abstract

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