Effects of Progesterone Supplementation During the Non-Breeding Season on Reproductive Performance of Ewes Under Heat Stress Conditions

Document Type : Complete scientific research article

Authors

1 Tehran university

2 tehran university

3 zanjan university

Abstract

Background and Objectives: In Iran, sheep play a significant role in the supply of red meat. Increasing lamb production per breeding ewe is one of the key factors in meeting the country’s demand for red meat. Therefore, improving lambing rates and enhancing reproductive efficiency are of great interest to researchers. Global warming significantly impacts the reproductive performance of sheep. Current estrus synchronization protocols may not be efficient under heat stress (HS) conditions, particularly during non-breeding seasons. Identifying effective strategies to mitigate the negative effects of HS on reproduction is crucial for improving sheep productivity. This study aimed to evaluate the impact of severe HS on the effectiveness of estrus synchronization protocols using intravaginal devices (IVDs) impregnated with varying doses and types of progesterone in ewes during the non-breeding season.
Materials and Methods: This study evaluated the impact of severe HS on the effectiveness of estrus synchronization protocols using intravaginal devices (IVDs) impregnated with different doses and analogues of progesterone in Sangsari ewes during the non-breeding season. Eighty healthy, non-pregnant ewes were randomly assigned to four experimental groups: Control (CIDR with 330 mg progesterone without HS), HS-CIDR330 (CIDR with 330 mg progesterone under HS), HS-SP60 (sponges with 60 mg medroxyprogesterone acetate under HS), and HS-SP800 (sponges impregnated with 800 mg progesterone under HS). The ewes in HS groups were housed in warm rooms (temperature-humidity index >79) for 9 hours daily (9 AM to 6 PM) for five days before and five days after mating, while the control group remained under thermoneutral conditions without HS. Ewes received IVDs for seven days, followed by an intramuscular injection of 500 IU of pregnant mare serum gonadotropin (PMSG) upon device removal. One day after device removal, rams were introduced to the ewes. Rectal temperature was measured, and blood samples were collected daily throughout the experiment. Serum progesterone levels were measured using conventional ELISA kits. Reproductive performance indices, including estrus rate, pregnancy rate, return to estrus rate, lambing rate, and twinning rate, were recorded.
Results: The results showed that under HS conditions and during the non-breeding season, higher progesterone concentrations in IVDs significantly improved pregnancy, lambing, and twinning rates. In contrast, synthetic analogues such as medroxyprogesterone acetate and lower doses of progesterone failed to achieve similar outcomes. Additionally, rectal temperatures were higher in the HS groups compared to the control group, and serum progesterone levels were significantly higher in the Control and HS-SP800 groups compared to the other groups.
Conclusion: Increasing the concentration of natural progesterone in IVDs, especially under severe HS conditions and during non-breeding seasons, appears to be an effective strategy for improving the reproductive performance of sheep. This approach holds promise for improving productivity in regions facing climate challenges.

Keywords

Main Subjects

Journal of Ruminant Research
Volume 13, Issue 3
December 2025
Pages 187-201

Files

Share

How to cite

Statistics