360 THE EFFECTS OF PROGESTERONE AND PRESENCE OF CORPUS LUTEUM ON SUPEROVULATION IN BEEF CATTLE (BOS TAURUS)

Abstract

Bovine embryo transfer is a multi-million dollar industry that relies on hyperstimulation of cattle ovaries with exogenous follicle stimulating hormone (FSH). This process is variable among donors, breeds, and embryo transfer organizations. Historically, donor cattle are administered FSH (IM; <15 to 50 mg) for 4 days and a luteolytic dose of prostaglandin F2± (PGF2±; IM; 25 mg twice daily) on Day 3. The presence of a functional corpus luteum (CL) is crucial for this protocol; however, there are embryo donor cattle that do not exhibit progesterone indicative of a functional CL. Experiment 1 was performed to determine whether the number of embryos and ovulations that could be generated from donors without a functional CL might be increased by progesterone supplementation via a vaginal insert (CIDR). Experiment 2 was performed to determine an optimal FSH (Sioux Biochemical, Inc., Sioux Center, IA, USA) dosage (high dose = 30 units, n = 9; low dose = 20 units, n = 7) for cattle without a functional CL. Embryos were collected nonsurgically by uterine lavage and were evaluated morphologically according to the IETS system. Progesterone concentrations were determined using an RIA on venous blood samples (10 mL). Ovulations (as evident by resulting CL) were counted using transrectal ultrasonography. Embryo, ovulation, and progesterone data were analyzed using ANOVA with SAS (SAS Institute, Inc., Cary, NC, USA), to evaluate the main effects of group and time (progesterone concentrations only). In Experiment 1, there was no difference in the number of high-quality embryos that were recovered from hyperstimulated (IM; 35 units) Angus-cross cattle that either had a functional CL (n = 12) or a CIDR insert (n = 12) following PGF2± injection. Progesterone concentrations were similar until Day 3 (Day 0 = injection of PGF2± and CIDR insertion). On Day 3, the CL group had higher (P < 0.05) progesterone concentrations (3.5 ± 0.4 ng/mL) than the CIDR group (1.5 ± 0.1 ng/mL). Further, there was no difference between the average number of ovulations for the cows with a CL (22.5 ± 2.4) or cows without a CL (22.8 ± 1.5). In Experiment 2, there was no difference in the number of high-quality embryos recovered from cattle in the high-dose group (8.1 ± 0.4) compared to cattle in the low dose group (5.7 ± 1.3). There were no differences during the treatment period in progesterone concentrations between high- and low-dose groups. Although there was no statistical difference in the number of ovulations between cattle in the high dose group (20.2 ± 2.5) compared to cattle in the low dose group (15.6 ± 0.9), the higher FSH dose did yield over 30% more ovulations. Embryo collection from cattle that do not show signs of a CL can increase the number of offspring and embryos, and the genetic progress of otherwise unavailable cattle, thus benefiting the beef and beef cattle industries.