Effect of two hormonal progesterone-based protocols on ovulation rate and occurrence on anovulatory estrous in crossbred tropical cows

In order to study the effects of intravaginal sponges impregnated with Medroxi-progesterone acetate (MAP) on ovulation rate and anovulatory estrus rate, an assay was carried out in a commercial farm located at the Rosario de Perija county, Zulia state, Venezuela. Noncycling crossbred cows (B. taurus x B. indicus, n = 61) between 40 and 47 days postpartum were randomly allotted into one of three treatments: Progesterone plus Estradiol (MAP+E, n = 20); Progesterone plus GnRH and PGF(2)alpha (MAP+GnRH, n = 21) and Control (T, n = 20). The studied variables were: ovulation rate (TO), Anovulatory estrus rate (TCA), Progesterone levels (NP) and Corpus Luteum diameter (DCL). Progesterone concentrations in milk were measured by RIA to determine ovulation after sponge removal. The variables TO and TCA were analyzed using frequency procedures and chi-square test of SAS. The NP and DCL were analyzed by ANOVA using GLM procedure of SAS. The TO was increased (P < 0.05) in MAP+GnRH (57.1%) vs 25% for MAP+E and T. The MAP+E had increased TCA (P < 0.05; 66,7%) compared to MAP+GnRH (21,4%), which was similar to T, where all cows ovulated following estrus. No effects of treatments on NP and DCL in ovulating cows were observed. In conclusion, cows treated with MAP+E had an increased anovulatory estrus rate, suggesting a negative effect on estrus-ovulation ratio in noncycling crossbred cows during early postpartum. On the other hand, MAP combined with GnRH and PGF(2)alpha improved the ovulation rate and percentage of ovulatory estrus.