Milk production and composition of conventional and organic-fed Holstein dairy cows as affected by temperature and relative humidity

This study aimed to determine the effects if ambient temperature (Ta), relative humidity (RH), and temperature-humidity index (THI) on milk production parameters such as milk yield, fat, protein, milk urea nitrogen (MUN), and lactose. A total of fifty (50) mid-lactating Korean Holstein cows (144 - 150 days postpartum) were randomly assigned to two groups in equal numbers (n = 25) according to the type of diet received: conventional feed, a mixture of 56: 44 ratio of roughage and concentrate mix, and organic feed containing 100% organic roughage. Temperature, RH, and THI were recorded daily and averaged monthly. Conventional group showed higher dry matter intake throughout the experiment and thus, showed higher total milk yield and milk composition such as milk fat, protein, and lactose content than organic milk. Milk of the conventional group showed higher polyunsaturated fatty acid concentration. Highest milk yield was observed in September (21.7℃, 82.4%RH) in conventional group (27.69 kg·day^-1) and in June (21.4℃, 72.9%RH) in organic group (14.31 kg·day^-1). In conventional group, milk yield was positively correlated with Ta and THI, and milk protein was negatively correlated with Ta, RH, and THI. In organic feeding, only the MUN among milk composition parameters showed a significant correlation where it showed a negative correlation with Ta, RH, and THI. Conventional feeding showed significantly higher milk yield, fat, protein, and lactose than organic feeding throughout the experiment, although, organic feeding showed to be less likely affected by Ta, RH, and THI than the conventional feeding.