Attention to dry matter intake this summer — in addition to proper cow cooling — can help minimize the impact of heat stress on your cows’ dry matter intake.

According to research conducted at the University of Georgia Coastal Plain Experiment Station, Holstein cows exposed to extreme heat-stress conditions — those classified by a temperature-humidity index (THI) of 72 or greater — ate about 0.5 pounds less feed per day for every degree increase in THI, explains Joe West, dairy scientist at the University of Georgia Coastal Plain Experiment Station. Consequently, milk yield declined about 0.9 pounds per day for every degree increase in THI.

The following table describes the range of temperatures and relative humidity levels that result in a THI of 72 or 76:





















Temperature Relative Humidty THI
72 F 100 % 72
74 F 80 % 72
76 F 60 % 72
80 F 35 % 72
84 F 15 % 72
76 F 100 % 76
78 F 80 % 76
80 F 70 % 76
84 F 45 % 76
88 F 25 % 76