Date of Graduation

2015

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

Marlon Knights

Committee Co-Chair

Joseph S Moritz

Committee Member

Matthew E Wilson

Abstract

Traditionally, prostaglandin F2alpha (PGF2alpha) has been included in short-term progesterone-based estrous synchronization (STPBES) protocols but its inclusion has been associated with a reduction in fertility at the synchronized estrus. Also, previous studies have shown that there are differences in the endocrine status and follicular dynamics of ewes at different stages of the estrous cycle, although effects have not been sufficiently evaluated regarding the reproductive outcomes when luteolysis is induced on different days of the cycle. To evaluate the effect of time of application of PGF2alpha relative to the progesterone treatment on fertility, ewes (N=442) from 4 farms located in WV and PA were randomly assigned to receive controlled internal drug-releasing devices (CIDR-g; 0.3 g progesterone) for 5 days alone (n=123; treatment 1), in combination with 25 mg PGF2alpha (5 mL Lutalyse; Dinoprost Tromethamine; Zoetis) at CIDR insertion (n=103; treatment 2) or removal (n=100; treatment 3), or 25 mg PGF2alpha alone (n=116; treatment 4) prior to being joined with sexually mature rams. To compare reproductive performance in ewes treated with PGF2alpha at different stages of the estrous cycle, ewes (N=148) from 1 farm located in southwestern PA were pre-synchronized using treatment with a CIDR device for 7 days. Ewes were randomly assigned to receive a 25 mg intramuscular injection of PGF2alpha 7 (n=48), 10 (n=50), or 13 ( n=50) days following CIDR removal which was projected to be equivalent to day 5, 8, and 11 of the estrous cycle. Ewes were then joined with sexually mature rams on the day of PGF2alpha injection. Data were analyzed using analysis of variance with the model consisting of the main effects of treatments, farms and their interactions and additionally, least square means for treatment effects were determined. Estrous response did not differ among ewes receiving progesterone-based treatments but was significantly lower in ewes receiving PGF2alpha only. Pregnancy rate to first service was highest in ewes receiving CIDR only. The percent of ewes lambing to first service was greater in ewes treated with CIDR only than in ewes treated with PGF2alpha (p=0.05). In experiment 2, the mean estrous response was 85.1% and did not differ with treatment. Conception rate was higher in ewes treated with PGF2alpha at predicted day 5 than those injected at day 11 (p<0.05) and tended to be higher than ewes injected on day 8 (p<0.1). Pregnancy rate to first service tended to be higher in day 5 than day 11 ewes (p=0.07), and more ewes lambed to first service when treated at day 5 than at either day 8 or 11 (p=0.05). First service prolificacy was also greater in ewes treated at predicted day 5 than those injected on day 11 (p=0.05) and tended to be higher than that of ewes injected with PGF 2alpha at predicted day 8 (p=0.14). In conclusion, application of PGF2alpha at the beginning or end of progesterone pretreatment did not enhance synchrony of estrus or other reproductive outcomes and synchronization of estrus with a 5 day treatment with progesterone was sufficient to synchronize estrus with higher fertility. Additionally, application of PGF2alpha earlier in the estrous cycle resulted in improved reproductive performance.

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