A 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<0.01) effect of sampling days in all 4 protocols with higher values on day of PGF2α injection and on day 12 post-AI compared to day 0 and day of FTAI. Moreover, the mean plasma progesterone concentrations were found to be significantly (P<0.05) higher in conceived than non-conceived cows on day 12 post-AI under all 4 protocols. No significant influence of sampling days and conceived-nonconceived status of cows was observed on plasma protein profile in any of the groups studied. The overall mean plasma cholesterol concentration (mg/dl) for cows under Ovsynch and Ovsynch Plus protocols were 140.74±3.29 and 151.72±3.78, respectively, which did not vary significantly between sampling days. Under Estradoublesynch protocol, the period effect was significant with higher cholesterol during luteal phase of cycle. The non-conceived cows had consistently higher mean cholesterol than conceived cows on all sampling days in all groups, but differed significantly (P<0.05) in Ovsynch protocol with pooled means of 148.85±3.33 vs. 121.80±4.23 mg/dl, and in Doublesynch protocol 174.20±5.61 vs. 150.50±7.90 mg/dl. The results showed that Doublesynch protocol is better with respect to modulation of plasma progesterone and cholesterol profile and conception rate in repeat breeding cows.