| Lactose in milk has relatively low variation regardless of season, breed, or country. The study of lactose concentration and correlation among other milk components is limited. Furthermore, dairy farmers have limited access to the lactose data and are not familiar with it. This study was conducted to: 1) investigate the phenotypic correlation between lactose and other milk components; and 2) determine the importance of lactose for dairy herds.;Monthly DHIA records from Utah (DHIA), Dairy Herd Performance Test (DHTP) records from Ibaraki, Japan, and California herd average data (CHAD) covering 27 states were used to analyze the relationships between milk lactose concentrations and parameters related to milk production. Record spans for each data sets for DHIA, DHTP and CHAD were 7 consecutive years ending August 2017, 12 consecutive years ending August 2017, and 9 consecutive years ending August 2017 respectively.;Means for the DHIA records were 187.9 days in milk, 34.6 kg/d milk yield, 4.08% lactose, 3.88% fat, 3.15% protein, 8.86% SNF, 14.4 mg/dl MUN, 256,000 SCC, and 2.4 parity. A negative correlation was observed between lactose concentration and parity (r = -0.27). Positive phenotypic correlations between lactose percentage and milk yield (r = 0.28), and negative correlations with fat (r = -0.17), protein (r = -0.21) and SCC (r = -0.30) were observed. No seasonal fluctuations of milk lactose concentrations were observed.;Mean for the DHTP records were 4.55% lactose, 3.95% fat, 3.29% protein, 8.74% SNF, 283 mOsm/kg osmotic pressure, 19,600 bacteria count, and 222,000 SCC. A seasonality in the lactose concentrations were observed, with the lowest concentrations of lactose observed in late summer and fall. There were no phenotypic correlations between lactose concentrations and protein, but a negative correlation with fat (r = -0.12) was observed. A significant negative correlation with SCC (r = -0.28) was also observed.;Based on the CHAD records, cows with lower lactose concentrations showed a higher culling rate, which indicates that the milk lactose concentration could be a potential indicator of problems in a dairy herd. This study suggest that lactose level could be an indicator for managing dairy farms. Dairy farmers should be able to access lactose data, and these data should be provided by DHIA. |
