This study was carried out at a private farm, Dakahlia governorate during the period from November 2013 to April 2014 to evaluate the effects of oxytocin (OXY) and prostaglandin (PG) on uterine involution and consequently on postpartum productive and reproductive performance of primiparous Friesian cows. Total of 15 primiparous cows with live body weight (380-420 kg were divided into 3 groups, 5 in each. Animals were i.m. injected with saline solution (control, G1), 50 IU OXY (G2) and 3 ml PG (Estromate, G3) within 12 h post-calving. Routine examination of the genitalia per rectum was conducted once weekly to judge the uterine involution by ultrasonography to determine diameter of uterine horns (gravid and non-gravid), cervical diameter and vaginal length on day 10, 15, 22, 27 and 32 of postpartum period. Animals were hand milked twice/day and those in heat were naturally inseminated and pregnancy was diagnosed by rectal palpation on day 45 post-insemination. Postpartum 1st estrus (PPFEI) and service (PPFSI) intervals, estrus (ER) and conception (CR) rates, days open (DO), number of services/conception (NSC), and service period length (SPL) were recorded. Results showed that diameter of non-gravid horns showed insignificant group differences. Diameter of gravid horns was wider (P<0.05) in G1 than in G2 and G3 from 10- up to 32-day postpartum, indicating earlier uterine horn symmetry in treatment than in control groups. Postpartum interval required for symmetry in gravid and non-gravid horns was shorter in G3 and G2 (21.4 and 20.9 d) than in G1 (28.7 d), respectively. Cervical closure was completed earlier in G2 (22.8 d, P<0.05) and in G3 (25.5 d, P≥0.05) than in G1 (28.6 d). Resumption of vaginal length had similar interval in all experimental groups, ranging between 18 and 19 d. Cows in G2 showed higher (P<0.05) ER (100 vs. 80%) and CR (80 vs. 60%), lower NSC (1.75 vs. 2.30 serv.), and shorter SPL (15.75 vs. 28.33 d) than in G1. Cows in G3 increased ER (80 vs. 100%) and decreased DO (52.33 vs. 98.0 d) as compared to G1, but insignificantly improved other reproductive parameters. Milk yield as total or daily milk yield was not affected significantly by treatment.
Based on the foregoing results, oxytocin injection (i.m.) within 12 h post-calving produced early uterine involution and markedly affect in positive trends on the reproductive performance of Friesian cows without pronounced effect on milk yield.