Whether you farm near the Rockies or the Everglades, most of you have seen the effects of heat stress on your cows. They might be exposed for different lengths of time — ranging from one week to five months — but very few will avoid it entirely.
Over the years, much has been written about how heat stress affects dairy cows. This article will discuss nutrition and management strategies that have been tested, researched, and used successfully. But first, we want to emphasize that cooling cows with water and air movement should be your top priority. None of our recommendations will work well unless the cows are cooled first.
Causes and effects of heat stress . . .
We know that all cows experience heat stress when temperatures rise above 78 degrees. However, the amount of stress largely depends on humidity, shade, and air flow. We believe that while 78 degrees is generally about right for most cows, heat stress for others can actually begin at lower temperatures, around 70 degrees. We encourage our producers to err on the side of caution and to begin using fans and sprinklers as soon as cows look hot.
The most obvious indicator of heat stress is the head-down, panting behavior. However, heat stress causes many other noticeable behavior changes as well, such as bunching, standing half in and half out of free stalls, lethargy, and water guarding. Many times we find these behaviors hard to explain and, more importantly, hard to correct.
To a cow, perception is reality. Sometimes this perception of comfort during hot weather can result in bunching behavior. If cows perceive direct sunlight entering the barn at a given time of day as “hot,” they will often bunch to avoid the rays. Although this behavior doesn’t make sense to us, the cows themselves may see it as a logical response to their perception that direct sunlight is responsible for their discomfort.
In addition to bunching, we may observe more cows that stand half in and half out of a free stall. Perhaps at one point the cow was able to take advantage of a breeze at that height above the stall. This may have occurred two to three days ago, but she may continue this behavior in the hope that it might happen again. Unfortunately, the negative effects of standing longer are often not seen until after the heat stress is over. Remember, there can be up to an eight-week lag-time between cause and effect in hoof problems, explaining the spike in lameness in early fall.
Water guarding can be another behavioral response to heat stress. A dominant cow can deny access to water for a high percentage of the cows housed together if she perceives that it is a scarce resource.
In terms of nutrition, cows will respond by reducing dry matter intake (DMI) while they increase their water consumption by as much as 100 percent. At the same time, cows begin sorting more and chewing their cud less which takes away an important buffer in the blood system. All of these effects are the perfect trifecta for rumen acidosis, and we all know what acidosis does to dairy cows.
Start with nutrition . . .
The main nutritional problem in times of heat stress is meeting a cow’s nutritional requirements in a shrinking space. Several options for solving this problem are commonly discussed, but we have some reservations about which ones work.
• Add more grain — There is no question that adding more grain to a diet usually results in a quick gain in production and intake, but it may have devastating long-term consequences. We believe that increasing starch levels is ultimately not a good idea because the result is often an unbalanced rumen. We are not aware of any research that supports this strategy and don’t recommend it.
• Increase protein concentration — As the old adage goes, cows eat amounts, not percentages. Cows have protein requirements that are reported as amounts. The strategy of raising the percentage of crude protein (CP) in a diet addresses the fact that dry matter intake (DMI) is declining, so the protein consumption holds steady. While this seems logical, we are cautious about inconsistent protein levels within a herd. A ration that is formulated, fed, and digested as balanced between protein and energy is our first responsibility. We do not believe in quibbling over individual nutrient requirements at the expense of an unbalanced rumen.
Several good possibilities do exist for solving the nutritional dilemma posed by heat stress:
• Add fat — This strategy uses the high caloric density of fat (four times that of corn) to make up for a shortfall in energy. This strategy is attractive because fat does not ferment into lactic acid. However, producers should note there are rumen-protected and unprotected fats. Remember, fat is not friendly to fiber digestion in the rumen. We typically use rumen-protected fat to bring the total ration fats levels to no more than 7 percent as a way to meet energy requirements, while avoiding the negative effects of fiber digestibility.
• Increase the mineral concentration — During heat stress, cows can become deficient in minerals much like athletes during strenuous exercise. We like the strategy of raising mineral concentration because it is backed by plenty of research, and we personally know what it feels like to cramp up from a lack of potassium. The current recommendation is to use sodium and potassium bicarbonate rather than chloride because excess chloride levels may reduce intake and performance. Most of our rations contain 0.5 pounds of sodium bicarbonate which usually takes care of the sodium requirements.
• Use feed additives — We recommend one feed additive that is particularly useful for addressing heat stress: yeast culture. While there is a wide range of opinions on how yeast works, there are several common themes across most of the research. First, yeast culture increases intake; second, it improves fiber digestion; and third, it prevents acidosis by reducing lactic acid levels in the rumen. These are exactly the effects we need during heat stress. We also use “live” yeast culture as a competitive inhibitor to the “bad” yeasts (ex. Candida) that are common in fermented feed during the summer.
Keep cows cool . . .
In addition to nutritional changes, many of the negative behaviors of a cow responding to heat stress can be minimized by making simple management adjustments.
• Stall surfaces — Cows want to be clean, dry, and comfortable. Any extra effort during times of heat stress to maintain a proper amount of bedding will help to maximize stall usage and minimize the number of cows standing half in and half out of stalls. Remember that in a tie stall barn, the cow does not have a choice of comfort, so it is up to managers to bring comfort to her.
• Water quality and quantity — Dairy cattle suffer more quickly and severely from a lack of water than from deficiency of any other nutrient. Given this fact, we want to ensure that, in times of heat stress, we do not limit water and that waterers have good recharge and are kept as clean as possible. Many tie stall water bowls in use today are good examples of facility aspects that do not meet the needs of our cows.
• Shading — Watch the barn as the sun moves through the sky and see how much reaches into the barn. Do the cows seem to be reacting to these light changes? Opening and closing end doors for short periods at certain times of day might change this light without stopping airflow entirely and may help to control bunching behavior.
• Fly control — It never fails, our first bout of heat stress coincides with a major fly hatch. Keeping ahead of this coincidence will pay off in the long run, because nothing pushes cows together more than a fly problem.
• Time budget — Watch milking time, especially the time cows spend packed in a holding pen. Research has shown that a cow’s body temperature is hottest in the holding pen. This means two things: first, investing in holding pen and parlor exit lane cooling is an excellent idea; and second, minimizing the time cows spend in holding pens should help to minimize their rise in body temperature.
Heat stress will affect every farm in some shape or form. Look to well-researched strategies to combat it and stay away from quick fixes. You, and your cows, will be happier and healthier in the long run.