Investigation of negative energy balance and postpartum anoestrus in an intensive dairy farm from the Chinese province of Heilongjiang

The aim of this investigation was to determine the relationship between postpartum anoestrus and negative energy balance in an intensive dairy farm from the Heilongjiang Province, China. At 14 to 21 d after parturition, 100 cows were randomly selected and their plasma indices, including β-hydroxybutyric acid, non-esterified fatty acid, and glucose were measured. Cows were assigned to a positive energy balance group (n = 37) and a negative energy balance group (n = 36) based on their β-hydroxybutyric acid concentrations (> 1.20 mmol/l). The two groups of cows were examined by B-mode ultrasonography and rectal examination from 60 to 90 d after parturition to identify the ovarian status of oestrous and anoestrous animals. The incidences of negative energy balance and positive energy balance were 49 and 57%, respectively, from14 to 21 d after parturition. From 60 to 90 d after parturition, 94.4% of the negative energy balance group were in anoestrus and 5.6% were in oestrus, while 62.2% of the positive energy balance group were in anoestrus and 37.8% were in oestrus. Furthermore, the proportion of inactive ovaries in the negative energy balance group was 61.8%. In conclusion, the negative energy balance is an important factor causing inactive ovaries in high-yielding dairy cows.