Reproductive Response of Hair Sheep to Short or Long Duration Estrus Synchronization Protocols

Abstract

Objective: Evaluate the reproductive response of hair ewes treated with estrus synchronization protocols that included a progesterone-releasing intravaginal device (CIDR) for a period of 7 or 12 days.

Methodology: During the end of winter, ewes were randomly allotted to one of two estrus synchronization protocols: 1) Short-term protocol (SD), ewes (n=24) received a CIDR on Day 1 and removed on Day 7, and received 400 IU of equine chorionic gonadotropin (eCG) and 0.125 mg of cloprostenol; 2) Long-term protocol (LD), ewes (n=24) received a CIDR on Day 1, retired on Day 12 and received 400 IU eCG. Ewes showing estrous behavior were bred with a mature ram.

Results: There were no differences (P>0.05) in the estrus response in both groups of ewes (100 vs 95.8% for SD and LD, respectively), the pregnancy rate (87.5 vs 87.5%), prolificacy (1.95+0.1 vs 2.2+0.1 lambs/ewe), hours between CIDR removing and the beginning of estrus (34.4+8.1 vs 34.8+9.2 h), and estrus duration (39.7+2.9 vs 39.9+4.7 h). At CIDR removal, ewes in the PL group showed a greater diameter (P<0.05) for the largest follicle in both ovaries (5.42+0.3 and 5.42+0.4 mm for the follicle in the left and right ovaries, respectively) vs PC ewes (4.25+0.1 and 4.29+0.1 mm).

Limitations of study: Results observed in the follicle diameter could be due to low circulating progesterone levels in the LP group, which must be confirmed in future studies.

Conclusions: The short protocol for estrus synchronization can be used in hair ewes under temperate conditions, without affecting their reproductive response.