The Thai Journal of Veterinary Medicine


The presentinvestigation was carried out to demonstratethe effect of high ambient temperature (HTa) on lactation performance with herd-based measurement. One large dairy farm in Thailandwith more than 300crossbred Holstein cows milking each monthwas selected. The meteorological data was recorded once a week during the period of observation. Milking cows (n=90) were observed for a 10-month lactation curve based on their calving seasons: Summer, rainy and winter. The lactation curve was fitted by nonlinear regression using the reduced lactation persistency model.The climatic conditions revealed a high degree of temperature and humidity index (THI). The average THI throughout the year was 84.8 ± 0.5. The THI from summer (86.9 ± 1.0) was significantly higher than that from winter (82.7 ± 0.5, P<0.05). An analysis of the average lactation curve revealed that the total 305-day lactation yield (5407 kg) from this farm was higher than the average phenotypic 305-day lactation yield from dairy cows fed in Thailand (4698 kg). Lactation curves from different seasons revealed the potential effect of HTa on mammary gland function. Specifically, the area on the curve of the summer lactation curve was significantly lower than that of the winter curve by16%(P<0.05).This effect was apparently from the shortest lactation persistency. In conclusion, dairy cows fed in Thailand were under a high degree of HTa and had compromised lactation performance. Lactation persistency appears to be one of the main phenotypic traits for breed selection for dairy cows fed in the tropical country.



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