Estrus resynchronization in ewes with unknown pregnancy status.

Area of Science:

• Reproductive biology
• Animal science
• Veterinary medicine

Background:

• Fixed-time artificial insemination (FTAI) protocols are established for sheep, but estrus resynchronization strategies have not been previously investigated.
• Estrus resynchronization is crucial for optimizing breeding efficiency and genetic gain in sheep farming.

Purpose of the Study:

• To evaluate the impact of estrus resynchronization with exogenous progestogen on endogenous progesterone levels in ewes.
• To compare pregnancy rates in ewes undergoing two consecutive estrus synchronizations.

Main Methods:

• Experiment 1: Ewes received an intravaginal device (IVD) with medroxyprogesterone acetate (MPA) for 10 days, followed by eCG administration and either no further treatment or resynchronization from day 12 to 19.
• Experiment 2: Ewes underwent a first synchronization, followed by artificial insemination (AI) or natural mating (NM), and were then divided into control (no further treatment) or resynchronization groups before a second breeding.
• Experiment 3: Ewes were bred using two consecutive FTAI protocols within a 20-day interval.

Main Results:

• Progesterone levels showed no significant difference at days 12 and 19 but were higher in the control group at day 15.
• Cumulative pregnancy rates did not differ significantly between control (67.3%) and resynchronized (62.3%) ewes in Experiment 2.
• Pregnancy rates after the first (30.1%) and second (36.2%) FTAI in Experiment 3 were comparable.

Conclusions:

• Estrus resynchronization in ewes is a viable reproductive strategy.
• Exogenous progestogen supplementation for resynchronization, despite affecting progesterone levels, did not compromise pregnancy maintenance.
• This approach, particularly when combined with AI using superior genetics, can accelerate genetic progress in sheep populations.