Click on “Download PDF” for the PDF version or on the title for the HTML version.

If you are not an ASABE member or if your employer has not arranged for access to the full-text, Click here for options.

In hot summer weather under tropical conditions, milking cows experience a decline in production due to the increase in both dry bulb temperature and relative humidity. Providing good shade associated with evaporative cooling help reduce the negative effects of the heat stress exposition (Bucklin et al., 1991). However under tropical weather, the normally occurring high values of relative humidity limits the use of evaporative cooling, and leaves fans or water spraying as one alternative for cooling the animals. The main disadvantage of water spraying over the cows is the excess of water that may lead to increase in the humidity inside the buildings. This research had the objective of evaluating the effect of the environment for a group of Holstein cows in a freestall system under tropical conditions. The trial had 460 Holstein milking cows and took place at a dairy farm located at an altitude of 750m, latitude of 22.14S and longitude of 46.74 W. The cows were selected by their milking yield and two groups were formed: the low production (LPC) for values = 20 kg of milk/cow/day, and the high production cows (HPC) for values =.21 kg of milk/cow/day. Dry bulb temperatures and relative humidities were recorded inside the freestall buildings from October 1999 to November 2000. Data were organized in a way to statistically verify the decline of milk production as function of dry bulb temperature and relative humidity and the time of the year. It was found that for HPC the decrease in production was not significantly related to dry bulb temperature or to the relative humidity values, while the LPC presented a significant decrease in production (a=0.05) related to the increase in the dry bulb temperature inside the housing, even though it did not present significant change in milk yield due to the relative humidity. Best yields were recorded during the months of April to July, Winter season, where the milk yield increase in average was 3.4 kg/cow/day. As the use of cooling equipment tends to reduce the inside temperature, even though the less productive cows (30% of the herd, 2.0 kg/cow/day) did not show a significant response to the decrease in the environmental temperature during the cooler months, the increase in the milk yield for the most productive cows (50% of the herd, 0.4 kg/cow/day) was found. Using cooling equipments it was found for the whole herd an average increase in milk yield of 4.2kg/cow/day, that may justify an investment in cooling devices.