Dairy cows increase heat loads when the temperature-humidity index (THI) value is elevated in the ambient environments. This condition often occurs in the tropical areas due to a higher THI rate throughout seasons. The major objective of the study was to investigate the different responses in milk yield and composition, chewing activities, and health parameters in dairy cows under the dry and wet seasons of tropical climate zone in Indonesia. Twenty mid-lactating Indonesian Holstein-Friesian cows (139.3 ± 24.63 DIM; 10 primiparous and 10 multiparous; 441 ± 21.5 kg BW) were randomly subjected to 2 groups, dairy cows under dry (n = 10) and wet season (n = 10). Both groups received the same diets throughout the experiment. To determine the heat stress condition, the THI values were recorded daily. Overall, a higher number of THI was more pronounced in wet season. A lower dry matter intake (DMI) and milk yield were observed in wet season group. A tendency towards higher milk protein contents was found in dairy cows under dry season compared to cows under wet season. The other milk compositions such as fat, lactose, and SNF remained unchanged in both dry and wet season groups. The comparison between both groups at several time points of eating and ruminating time revealed significantly higher in cows under dry season. Overall, a higher chewing per bolus was observed in cows under dry season than their counterparts. Furthermore, a tendential greater extent rectal temperature pointed in the wet season group compared to the dry season group relatively. Data suggest that a stronger heat stress condition in wet season was more pronounced compared to dry season, with adversely affecting stronger declined DMI, milk yield, and chewing activities of dairy cows.
Keywords: Chewing activities; DMI; Dairy cow; Milk yield; THI.
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