Session: Physiology and Endocrinology I

233 - Estrus Response and Pregnancy Rates of Beef Replacement Heifers Enrolled in Two Fixed-time Artificial Insemination Protocols, with or Without Pre-synchronization

Friday, July 16, 2021

8:45 AM – 9:00 AM EST

Location: Kentucky International Convention Center (KICC), M109 & 110

Presenting Author(s)

Vitor R G Rodrigues Gomes Mercadante, DVM, MS, PhD

Assistant professor and extension specialist
Animal and Poultry Sciences, Virginia Tech, Blacksburg, VA, USA; Large Animal Clinical Sciences, Virginia Tech, Blacksburg, VA, USA
Blacksburg, Virginia

PDF Slides and Audio

Author(s)

GL

G. Cliff C. Lamb

Texas A&M University
College Station, Texas
Nicky Oosthuizen, PhD

Reproduction Specialist
ABS Global
Sioux Falls, South Dakota
Nicholas W. Wege Dias

PhD student
Animal and Poultry Sciences, Virginia Tech, Blacksburg, VA, USA
Blacksburg, Virginia
Stefania Pancini, MSc

PhD Student
Animal and Poultry Sciences, Virginia Tech, Blacksburg, VA, USA
Blacksburg, Virginia
HH

Hannah Haines

Masters Student
Animal and Poultry Sciences, Virginia Tech, Blacksburg, VA, USA
Blacksburg, Virginia
JC

John Currin, Dr.

Clinical Associate Professor
Virginia Tech, Large Animal Clinical Sciences
Blacksburg, Virginia
SC

Sherrie Clark

Virginia Tech, Large Animal Clinical Sciences
Blacksburg, Virginia
JS

Jamie L. Stewart

Virginia Tech, Large Animal Clinical Sciences
Blacksburg, Virginia
GP

Gabriel J. Pent

Superintendent
Virginia Tech, Shenandoah Valley Agriculture Research and Extension Center
Raphine, Virginia
Matthew P. Holton, n/a

Graduate Student
University of Georgia
Athens, Georgia
Dylan B. Davis, MS

PhD Student
University of Georgia, Animal and Dairy Science
Athens, Georgia
SH

Shane R R. Hernandez

University of Georgia, Animal and Dairy Science
Athens, Georgia
RS

R. Lawton Stewart

University of Georgia, Animal and Dairy Science
Athens, Georgia
Pedro Fontes, PhD

Assistant Professor
University of Georgia
Athens, Georgia

Pre-synchronization strategies with prolonged exposure to exogenous progesterone have the potential to alter estrus expression and improve fertility in replacement beef heifers. The objective of this study was to evaluate the estrus response and pregnancy rate of beef heifers enrolled in two fixed-time artificial insemination (TAI) protocols. A total of 306 heifers (14 ± 2 months of age; 372 ± 24 kg body weight [BW]) at three locations were enrolled in the study. Within location, heifers were stratified by age and BW and randomly assigned to one of two treatments: 1) PG-CIDR54 (n = 152), heifers were administered prostaglandin F_2α (PGF; 25 mg) and a controlled internal drug releasing (CIDR) insert (Day -14), an injection of GnRH [100 μg (Day -7)], PGF injection and CIDR removal (Day 0), and a second injection of GnRH concurrently with TAI 54 ± 2 h later (Day 2); 2) 7-day CO-Synch+CIDR (CTRL; n = 154), heifers were administered GnRH (100 μg) and a CIDR insert (Day -7), PGF (25 mg) injection and CIDR removal (Day 0), and a second injection of GnRH concurrently with TAI 54 ± 2 h later (Day 2). All heifers received an estrus alert patch on Day 0 and were evaluated for patch activation at TAI on Day 2. Pregnancy was diagnosed by transrectal ultrasonography between 35 and 55 days after TAI. The percentage of heifers exhibiting estrus between Day 0 and 2 was greater (P < 0.01) in PG-CIDR54 compared with CTRL (77.0 and 39.6%, respectively). In addition, pregnancy rate to TAI tended (P = 0.08) to be greater for PG-CIDR54 compared with CTRL (48.0 and 38.3%, respectively). We conclude that beef heifers enrolled in the PG-CIDR54 protocol had increased estrus expression and tended to have greater pregnancy rate when compared with heifers enrolled in the 7-day CO-Synch+CIDR protocol.