Association of milk yield and body condition score indices with the commencement of luteal activity after parturition in high producing dairy cows

The aim of the present study was to investigate the relation between different indices of milk yield and body condition score (BCS) with the commencement of the luteal activity (C-LA) during the postpartum period in high producing dairy cows. Seventy-one multiparous healthy (free of detectable reproductive disorders) Holstein dairy cows (mean peak milk yield = 56. 7 ± 7. 4 kg) were used in the present study. Transrectal ultrasound scanning was performed twice weekly from the 1st to the 8th week postpartum. Blood samples were also collected twice weekly to measure serum progesterone (P4) concentrations. The BCS was monitored weekly after calving. Cows with serum P4 concentrations ≥1 ng/ml on at least 2 consecutive blood samplings were considered to have commenced luteal activity. The C-LA was observed in 51 out of 71 cows (71. 8%) earlier than 45 days postpartum، while 20 out of 71 cows (28. 2%) showed the C-LA later than 45 days postpartum. Among the indices defined for the milk yield pattern in the present study، difference in milk yield between the 1st week and the peak week and the peak of milk yield were significantly (P≤0. 05) lower in cows that commenced their luteal activity earlier than 45 days postpartum. Cows losing ≥1 unit BCS at the 3rd week postpartum showed their C-LA significantly later than those cows losing less BCS during the same interval (P≤0. 05). In conclusion، among the different indices defined for the milk yield and BCS in the present study، the higher milk yield at the peak and lower A-BCS (Area under the chart of BCS change) were the main factors associated with delayed commencement of luteal activity in clinically healthy high producing dairy cows.