This study was undertaken in field conditions on 50 repeat breeder HF crossbred cows to evaluate the efficacy of four estrus/ovulation synchronization protocols, viz., Ovsynch, Ovsynch Plus, Doublesynch, and Estradoublesynch (10 cows in each protocol, and in control) in terms of conception rate at induced estrus with fixed time AI (FTAI) and monitoring plasma progesterone, protein and cholesterol profile at different time intervals. All the cows received pre-synchronization treatment, i.e., Inj. 100 mg ivermectin s/c, Inj. tono-vita 10 ml each, single shot Inj. enrofloxacin 40 ml i/m, and bolus Minotas 1 daily for 7 days. The conception rates at induced cycle/FTAI were 30, 30, 40 and 20 %, respectively, with Ovsynch, Ovsynch Plus, Doublesynch, and Estradoublesynch protocols, and 10% in control group. The rests were taken as non-conceived cows. The overall mean plasma progesterone concentrations (ng/ml) compared on day 0 (start of treatment), 7/9/10 (PGF2α injection), 9/12/13(FTAI) and on day 12 post-AI in cows under different protocols revealed significant (P
Key words: Crossbred cows, Repeat breeding, Ovulation synchronization, Plasma progesterone, Cholesterol, Conception rate.