Synchronization of the estrous during a short period, using a low dose of equine chorionic gonadotropin (eCG) in primiparous and multiparous ewes


José L. Cordero-Mora
Teresa Sánchez-Torres
Teodulo Salinas-Ríos
Jorge Hernández-Bautista
José L. Figueroa-Velasco
José A. Martínez-Aispuro


Cronolone, estrous, sheep, progesterone, synchronization.


Objective: To evaluate the reduction effect of the synchronized luteal phase and the eCG application in the reproductive variables and hormone profile response of primiparous and multiparous ewes.

Design/Methodology/Approach: The experimental design was completely random, with a 2 × 2 × 2 factorial arrangement. Based on their reproductive activity, the 81 specimens were divided into primiparous (n=38) and multiparous (n=43) ewes. The estrous and pregnancy stages were analyzed using the c2 test. An analysis of variance and the Tukey’s mean comparison test were used to determine the start and the duration of the estrous. P4 concentration was measured using the PROC MIXED which influenced the fixed effects of the treatment and the day, as well as their interaction.

Results: There was no difference between treatments, regarding the occurrence of the estrous; however, its start and duration were not impacted by the physiological state and the synchronized luteal phase. P4 concentrations in plasm were higher in primiparous ewes than in multiparous ewes. The main effects did not impact the pregnancy and the prolificity rates.

Study Limitations/Implications: The variation in the start and the duration of the estrous was caused by the physiological reproductive state and the duration of the synchronized luteal phase (6 and 12 days). Therefore, these effects should be taken into account when the artificial insemination takes place at a fixed period.

Finding/Conclusions: The combination of the cronolone sponges with 100 UI of eCG during short periods (6 days) effectively synchronizes the estrous. P4 concentrations in serum were higher in primiparous ewes, although these concentrations were not a determining factor in the increase of pregnancy and prolificity.

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