Resumen

MARTINEZ TINAJERO, Jaime Jorge et al. Reproductive Performance in Blackbelly Ewes Synchronized With MPA and eCG During the Low Fertility Season. Rev. Cient. (Maracaibo) [online]. 2007, vol.17, n.1, pp.47-52. ISSN 0798-2259.

The experiment was carried out to evaluate the effect of different time of eCG administration on the reproductive performance of Blackbelly ewes of second lambing and 24.2±2.7 months of age and 32.6±3.9 kg of body weight, which were subjected to estrus synchronization protocols with intravaginal sponges impregnated with 65 mg of medroxiprogesterone acetate (MPA) for 12 days in the non breeding season (March and April) under the humid tropical environment of Mexico. The animals were randomly assigned to one of four treatments; T1 (n=15): Continuous breeding; T2 (n=15): 65 mg MPA + 200 U.I. eCG 48 h before sponges withdrawal + Controlled breeding; T3 (n=15): 65 mg MPA + 200 U.I. eCG at sponges removal + Controlled breeding and T4 (n=15): 65 mg MPA + 200 U.I. eCG at the moment of controlled breeding. The continuous variables were evaluated with the variance analysis under GLM procedures of statistical package SAS. The proportion variables were analyzed with chi square free test. The comparison of means was carried out with the honest test of Tukey. The estrus response was 40; 100; 100 y 100% for T1, T2, T3 and T4, respectively (P<0.05). The onset of the synchronized estrus did not show differences (P>0.05) and the interval were longer in T1 and T4 (51±28.5 y 42±10.8 h) than T2 and T3 (39.2±8.1 y 38.8±6.7 h). Significant differences were observed in pregnancy rates (40; 66.6; 80 y 60% for T1, T2, T3 and T4, respectively). Mean progesterone concentration (7.4±8.1 ng/mL) indicated that 25% of ewes were cycling at the beginning of the experiment. The results of this study show that the use MPA and 200 U.I. of eCG 48 h before sponges removal, at sponges withdrawal and at controlled breeding are efficient in synchronizing estrus in Blackbelly ewes during the non breeding season in tropical environment conditions of México

Palabras clave : Blackbelly; synchronization; estrus; MPA; eCG; reproduction.