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Session: Physiology and Endocrinology II: The Estrous Cycle, Breeding, and Embryo Transfer

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

Monday, June 27, 2022

1:05 PM – 1:20 PM CT

Location: Oklahoma City Convention Center, 301 A/B

Presenting Author(s)

Nicky Oosthuizen, PhD

Beef Reproduction Specialist
ABS Global
SIOUX FALLS, South Dakota

Author(s)

KP

Kristina Porter

Veterinarian
Porter Veterinary Service
Huron, SD
SB

Samir Burato

University of Georgia
Athens, GA
LM

Lucas Melo

Graduate Student
University of Georgia
Athens, GA
KP

Ky G. Pohler, n/a

Associate Professor
Texas A&M University
College Station, TX
Pedro Fontes, PhD

Assistant Professor
University of Georgia
Athens, GA
CL

Cliff C. Lamb

Texas A&M University
College Station, TX

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 F_2α (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.