ARE YOUR COWS REALLY ABLE TO ACCESS WATER DURING HEAT STRESS?

Heat stress changes more than respiration rate and milk production. As environmental temperature and humidity increase, cows also change how they compete for essential resources such as feed and water. While producers often focus on fans and sprinklers as the primary solutions, behavioral changes associated with heat stress can quietly reduce access to feed and water for certain animals in the pen. Understanding these behavioral shifts is important because the cows most affected are often not the dominant, high-performing individuals that are easiest to observe.

Heat stress occurs when cows accumulate more heat than they can dissipate. This commonly happens during periods of elevated temperature and humidity, and is often evaluated using the temperature-humidity index (THI). Traditionally, heat stress was thought to begin around a THI of 68 to 72, which roughly corresponds to environmental conditions near 68 to 77°F (20 to 25°C) depending on humidity. However, more recent work suggests cows may begin responding behaviorally at even lower thresholds. As heat stress develops, cows increase standing time, respiration rate, and water intake while reducing feed intake and rumination activity. These responses are attempts to reduce metabolic heat production and improve heat dissipation, but they also contribute to reduced milk production, impaired reproduction, altered feeding behavior, and an increased risk of health disorders.

One of the most consistent behavioral responses to heat stress is increased competition around cooling-related resources. A study from the University of British Columbia, led by Dr. Daniel Weary, evaluated drinking behavior in indoor-housed lactating dairy cows exposed to increasing THI conditions. Cows spent more time at the waterer, visited waterers more frequently, drank more water, and engaged in substantially more aggressive interactions as THI increased. Many of these behavioral changes became more apparent around THI values near 64 to 65, corresponding roughly to conditions around 64 to 68°F (18 to 20°C) under moderate humidity. These findings suggest that cows may begin altering behavior before obvious signs of heat stress or major production losses are observed.

The most important finding from that work may have been how subordinate cows responded. Cows with lower competitive success altered the timing of their drinking behavior during hot weather, shifting water consumption away from the hottest and most competitive parts of the day. During periods of elevated THI, dominant cows continued concentrating water visits during peak hours, while subordinate cows increasingly delayed water access until later evening periods when competition declined. This suggests that heat stress affects not only total water consumption, but also which cows can comfortably access water when they need it most.

From a management standpoint, this is important because water availability is not necessarily the same as water access. A pen may technically contain adequate water space, yet timid or subordinate cows may still avoid heavily crowded areas during periods of high competition. Similar patterns have already been demonstrated at the feedbunk, where subordinate cows alter feeding behavior to avoid dominant animals, often consuming feed later in the day when sorting has already occurred. Under heat-stress conditions, these behavioral shifts may further reduce the consistency of intake and compromise cooling opportunities for vulnerable cows.

Practical management strategies should therefore focus not only on cooling capacity, but also on reducing competition around key resources. Overstocking becomes more problematic during hot weather because cows concentrate their feeding and drinking activity into narrower periods of the day. Feed bunk space recommendations vary depending on stocking density and management style, but lactating cows under heat stress conditions generally benefit from approximately 24 to 30 inches (60 to 76 cm) of linear bunk space per cow whenever possible, especially in fresh and high-producing groups. Likewise, maintaining stocking density at or below 100% of stall capacity can help reduce competition for stalls and cooling resources during periods of elevated THI.

Water access also deserves special attention during hot weather. Industry recommendations commonly suggest at least 2 accessible water locations per pen, with approximately 3 to 4 inches (7.5 to 10 cm) of accessible trough perimeter per cow. Waterers should be positioned near feed areas and exit lanes from the parlor, where cows naturally seek water after eating and milking. High refill rate and cleanliness become especially important during summer because water intake can increase dramatically during hot periods.

Management of feed access is equally important. Increasing feed push-up frequency, delivering fresh feed during cooler parts of the day, and minimizing long periods where feed is present but physically inaccessible can help stabilize intake patterns. In overstocked pens, even small reductions in effective feed or water access may disproportionately affect timid cows.

Observation of cow behavior can also provide valuable information before major production losses occur. Pens with elevated crowding around waterers, excessive standing after milking, uneven feed access, or timid cows waiting to approach resources may already be experiencing meaningful heat stress effects even when environmental conditions appear only moderately elevated.

Heat stress management should not be viewed solely as a ventilation issue. It is also a competition and access issue. During hot weather, cows change how they interact with feed, water, and each other. Reducing competition and improving access to these resources may help stabilize intake behavior and improve cow comfort during periods of environmental stress.

— Daniel de Oliveira

doliveira@whminer.com