Estrus synchronization and follicular development patterns in jennies.

Overview

• This study evaluated the effectiveness of three hormonal protocols for estrus synchronization in two Chinese jenny breeds during different seasons.
• It also examined breed-specific patterns of follicular development to optimize breeding management.

Background and Objectives

• Reproductive efficiency in jennies is affected by both season and breed, but protocols tailored to major Chinese breeds are limited.
• The study aimed to compare three hormonal estrus synchronization treatments and to characterize follicular dynamics in DeZhou and Xinjiang jennies.
• It focused on assessing outcomes such as estrus occurrence, ovulation timing, conception rates, and follicular growth across spring (April-May) and summer (July-August).

Methods

• Two experiments were conducted with a total of 238 non-pregnant jennies:
• First experiment in April-May with 94 jennies.
• Second experiment in July-August with 144 jennies.
• Animals were assigned to one of three hormonal treatments:
• Treatment Group 1 (TG1): GnRH followed by PGFα at one injection timing.
• Treatment Group 2 (TG2): GnRH and PGFα but with a different injection timing.
• Treatment Group 3 (TG3): Combination of a Controlled Internal Drug Release (CIDR) intravaginal insert plus GnRH and PGFα.
• Measures taken included estrus rate, ovulation rate, and conception rate post-treatment.
• Follicular development was monitored daily via ultrasonography in a subgroup of 125 jennies (68 DeZhou and 57 Xinjiang) to record growth rates and follicle sizes.

Key Findings

• Estrus Synchronization Efficiency:
• TG3 (CIDR+GnRH-PGFα) in April-May produced the highest total estrus rate (85.0%), significantly greater than TG1 (53.0%) and TG2 (72.5%).
• Conception rates were similarly highest in TG3 (81.3%), surpassing both TG1 (66.7%) and TG2 (71.4%).
• Seasonal Effects:
• Overall reproductive outcomes, including estrus and conception rates, were better in the spring season (April-May) compared to summer (July-August).
• Breed Differences in Follicular Development:
• Xinjiang jennies showed a faster average follicular growth rate of about 5.52 mm/day compared to 4.32 mm/day in DeZhou jennies.
• DeZhou jennies developed larger pre-ovulatory follicles (nearly 45 mm) than Xinjiang jennies (around 31 mm).
• Ovarian Lateralization:
• No significant preference for ovulation on the left or right ovary was observed (left: 54.2%, right: 45.8%), indicating no lateral bias.

Conclusions and Implications

• The combined hormonal protocol using CIDR with GnRH and PGFα during spring is most effective for synchronizing estrus and maximizing conception in jennies.
• Recognizing breed-specific follicular growth dynamics can improve timing of insemination protocols, as Xinjiang and DeZhou jennies differ in growth rates and follicle sizes.
• The absence of ovarian lateralization suggests that ovulation occurs equally in both ovaries, simplifying management considerations.
• Overall, the findings support customized breeding strategies based on breed and season to enhance reproductive efficiency in Chinese jenny populations.