Effect of mid luteal administration of PGF2α on oestrus duration, serum progesterone profile and ovarian changes in crossbred cows exhibiting prolonged oestrus

The study compared oestrus duration, duration of follicular persistence, dominant follicle (DF) size, mid-cycle corpus luteum (CL) size and serum progesterone (P4) profiles between spontaneous and prostaglandin F2α (PGF2α)- induced oestrous cycles in crossbred cows exhibiting prolonged oestrus. Six apparently healthy crossbred cows under six years of age, within six months postpartum and exhibiting prolonged oestrus (24 h), were selected for the study. Transrectal ultrasonography (TRUS) was performed at 24 hr intervals from the onset of spontaneous oestrus until ovulation to assess DF size and follicular persistence, and again on day 10 post-oestrus to evaluate CL size, also all cows received 500 μ g of cloprostenol intramuscularly followed by TRUS during the induced oestrous cycle. Blood samples were collected on each day when TRUS was performed to determine serum P4. Data recorded before and after treatment were analysed using repeated measures ANOVA. No significant differences (p 0.05) were observed between spontaneous and induced cycles in oestrus duration (48.00 5.37 h vs. 44.00 5.06 h), duration of follicular persistence (60.00 5.37 h vs. 56.00 5.06 h), DF size (12.72 0.76 mm vs 13.37 0.39 mm), CL size (18.42 1.86 mm vs 18.40 1.56 mm) and serum P4 (0.51 0.08 ngmL vs 0.48 0.04 ngmL) concentrations. These findings suggest that PGF2α administration during the mid-luteal phase did not significantly influence morphology and function of ovarian structures in the induced oestrus in cows with prolonged oestrous. Non-significant serum P4 milieu after the treatment suggests incomplete luteolysis or presence of extra-gonadal sources of P4. Further, studies with a larger sample size are required to validate these results and explore more effective strategies to manage the prolonged oestrus in dairy cattle.