The current study was conducted to evaluate the effect of parity and days in milk on milk yield and milk production traits and their
correlation with β-hydroxybutyrate (BHB) concentrations in milk of Chinese tropic Holstein dairy cows which are adapted to a
humid subtropical climate in central China. About 3055 milking records of Holstein cows were obtained from three farms in the
hot region in the center of China. The records were classified according to parity to 4 categories: first parity, second parity, third
parity, and greater than third parity. According to days in milk, there were 4 groups, first group from (1–100 days), second group
from (101–200 days), third group from (201–305 days), and fourth group (>305 days). Milk samples collected between April and
November 2019 from the three farms were routinely checked for milk components including BHB using mid-infrared spectroscopy
a MilkoScan FT+ (Foss, Hillerød, Denmark). Data were analyzed by multivariate analysis of variance (generalized linear
model, GLM). Pearson’s correlation coefficients were used to measure the correlation between SCC and BHB with milk yield
and milk production traits. Results showed the significant effect of parity and days in milk on milk yield and milk production
traits. There was a negative effect of parity and days in milk on milk quality, with increasing parity and days in milk being
associated with higher somatic cell count (SCC) (P |
