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This study's objective Aim: This study aimed to compare the efficacy of two estrus synchronization methods in ewes conventional intravaginal progesterone sponges and a novel progesterone-loaded crosslinked chitosan microchip administered subcutaneously via the ear and to evaluate the effects of subsequent eCG or Vitamin E/Selenium (Vit. E/Se) supplementation on reproductive performance and hormonal profile.
Materials and methods: Thirty clinically healthy adult ewes (2–4 years old) were randomly allocated into two main groups (n = 10 each): Group T1, synchronized using intravaginal progesterone sponges (Chronogest CR) for 14 days, and Group T2, synchronized using subcutaneous progesterone-loaded chitosan microchips. Each group was further divided into three subgroups (n = 5): a single intramuscular injection of 500 IU eCG, a single intramuscular injection of 2 mL Vit. E/Se, or no treatment (control). Blood samples were collected at baseline, at device removal, and 24 hours post-treatment to determine serum progesterone, estrogen, FSH, and LH concentrations by ELISA. Estrus behavior was monitored using teaser rams, and reproductive performance (estrus response, pregnancy, lambing, fertility, and multiple lambing rates) was recorded. Data were analyzed by one-way ANOVA followed by Tukey's post hoc test (P ≤ 0.05).
Results: Estrus response was 100% across all groups regardless of synchronization method or treatment. Pregnancy, lambing, and fertility rates were lowest in the control group (40%), intermediate in the sponge + eCG group (80%), and highest in the sponge + eCG + Vit. E/Se and microchip + eCG groups (100% each), while the microchip + Vit. E/Se group achieved 60%. The microchip + eCG group also recorded the highest multiple lambing rate (100%). Both synchronization methods induced significant hormonal fluctuations (P ≤ 0.05), characterized by elevated progesterone during device application, a marked post-removal decline, and a subsequent surge in estrogen, FSH, and LH indicative of renewed follicular activity. The subcutaneous microchip group exhibited a more pronounced post-treatment hormonal rebound compared with the sponge group, suggesting more effective luteal priming.
Conclusion: The progesterone-loaded crosslinked chitosan microchip is an effective and reliable alternative to conventional intravaginal sponges for estrus synchronization in ewes, offering comparable or superior reproductive and hormonal outcomes, particularly when combined with eCG injection. These findings support the microchip's potential as an innovative, minimally invasive tool for reproductive management in small ruminants.