The aim of this study was to determine the effect of equine chorionic gonadotropin (eCG) applied in postpartum (pp) period on ovarian follicle development, serum estradiol concentration, serum progesterone concentration, the calving-to-first oestrus (calving-to-first insemination) interval, and conception at first insemination. The material of this study consisted of 20 cows on day 14 pp. Cows included in this study were randomly divided into two groups. Cows in the first group, were treated with eCG (500 IU Folligon; Intervet, Holland) for 14 days. No treatment was applied to the second group, and it was left as a control group, Ovarian follicle diameters were measured by ultrasonographic examination on days 14, 16, 18, 20 and 22 pp in all animals included in the study. Serum estradiol and progesterone were from blood samples taken on the same days. All animals included in the study were followed up until the first observable oestrus was detected, and they were inseminated 12 hours after the appearance of oestrus symptoms. A pregnancy examination was performed on the 45th day after insemination. In cows administered with eCG during postpartum period, an increase in ovarian follicle diameters compared to untreated cows and a decrease in the calving-to-first oestrus interval were determined. In contrast, serum estradiol and progesterone hormone levels did not differ between the two groups. Pregnancy rate in the experimental group was higher than that in the control group, but there was no statistical difference between them. As a result, it was concluded that eCG applied to dairy cows on day 14 pp did not affect serum estradiol and progesterone levels, but it affected the ovarian follicle diameter and the calving-to-first oestrus interval positively.
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