Abstract
The relationships among energy and protein intake, milk yield, body weight, and ovarian activity were investigated in postpartum Holstein cows with high milk production. Twenty-two Holstein cows with 8, 672±259(mean±SD)kg of 305-days average milk yield in the last (1st-6th) lactation were used. Milk progesterone levels were determined by enzyme immunoassay three times weekly for 70 days postpartum to estimate the day of first ovulation. Average 4% FCM yield per day during the 70 days in these cows was 35.8±0.6kg, reaching a peak (38.0±0.6kg) at around 30 days after calving. Levels of TDN and DCP intake for the 70 days period were averaged in 88±3% and 104±50%. In 20 of the 22 cows, ovarian cycles were reestablished within 70 days after calving. Average interval from parturition to the first ovulation in these cows was 26±2 days. The days of the first ovulation after calving (Y) was significantly correlated with average TDN (X) (r=-0.54, P<0.02) and DCP (X) (r=-0.64, P<0.02) levels and body weight loss during the first 6 weeks postpartum (X) (r=0.59, P<0.01). No significant correlation was observed between the days of first ovulation and average FCM yield during the first 3 weeks postpartum. These results indicate that levels of TDN and DCP intake, rather than milk yield, significantly influence the commencement of postpartum ovarian activity in high-producing dairy cows.
