How to Help Cows Rest, Eat, and Milk More During Heat Stress

New dairy research shows that positioning fans above freestalls to deliver cooling air flow at cow resting height can provide substantial benefits.

Cows prefer to spend at least half of their day lying down. In fact, lying time is so important that when resting space or time is in short supply cows will prioritize lying down over eating.

But when the temperature-humidity index (THI) rises, cows will sacrifice lying time and stand to try and cool down. Research shows that during times of heat stress cows’ lying time can drop by as much as 3 hours a day.

So how can we help cows get the lying time they need and prefer when Mother Nature turns up the heat? In addition to managing stocking density and cows’ time budgets, new research from the University of Wisconsin shows that fans properly placed to deliver cooling air flow to reach every freestall can improve lying time for lactating cows during times of heat stress.

The study was conducted in a naturally ventilated freestall barn in Wisconsin during the summer of 2020. Study pens were located in the northeast end of the facility to minimize the impact of local prevailing winds. In the study, two variable speed fans were positioned above each group of 8 head-to-head freestalls using roof mounted chains. Each fan was angled down to deliver air flow across all stalls in the group.

Three treatments were used:

  1. No fans (natural ventilation only);
  2. 60% fan power to provide 0.5 m/s of air flow; and
  3. 100% fan power to provide 1.5 m/s of air flow.

Fans were positioned to deliver appropriate air flow at cow resting height (1.6 feet above the stall surface).

Results showed that the average daily lying times were greatest in the 100% power fan group – 14.2 hours vs 13.9 hours for 60% fan speed vs. 13.2 hours with no fans. Researchers found that as the THI increased, lying time decreased for cows in the no fan group, but increased in both the 60% and 100% fan treatment groups.

In addition, fan-cooled cows had greater milk yield: 95 lbs/day for cows in the 100% fan power group, 94.1 lbs/day in the 60% fan power group, and 90.6 lbs/day for cows with no fans. Cows in both fan groups were able to maintain a more stable dry matter intake (DMI) during times of heat stress than cows in the no fan group. Cows in the 100% fan group ate on average 3.7 lbs more DMI per day than cows in the control group. Both groups of fan-cooled cows also had lower vaginal temperatures, lower respiration rates, and lower skin temperatures than control cows in the no fan group.

This study is the first to examine if fans placed over freestalls could improve lactating cow lying time during times of heat stress. Researchers concluded that when fans are properly positioned and calibrated to deliver a minimum of 1 m/s of cooling air flow at cow resting height across all stalls, lying time can be maintained, heat stress minimized, and milk yield and DMI improved.

The key is to deliver enough air flow at cow resting height to create an environment that favors heat loss from the cow while she is lying down. The effectiveness of fans for heat abatement varies depending on fan spacing, angle, and the air speed that reaches each cow.

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