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Nutritional strategies to enhance heat abatement in dairy cows

Marc-Antoine Guesthier for Progressive Dairyman Published on 30 April 2019

Heat stress reduces on-farm profits. Short-term impacts of heat stress can be easily measured by tracking milk shipments during and after a bout of excessive heat. During these periods, milk losses can reach up to 10 to 20 percent.

Figure 1 indicates, in yellow, the well-known symptoms of heat stress. However, the “invisible” consequences of heat stress, shown in red, are usually not observed until two to three months after a period of heat stress.



Effect of heat stress on dairy cows

These invisible consequences can cause a significant decrease in profits for a dairy farm. Lactating cows that experience heat stress will have reduced dry matter intake (DMI), milk yield and a shift in metabolism, which ultimately reduces the efficiency of milk production.

Heat-stressed dry cows similarly experience lower intakes, reduced mammary growth and compromised immune function that ultimately results in a poorer transition into lactation and lower milk yield (-6.7 kilograms per day) in the next lactation. Cooling dry cows has demonstrated a positive impact, increasing up to 5 kilograms per day milk production of their offspring.

Effect of heat stress

Recent studies on heat stress have shown the drop in DMI is responsible for only 40 to 50 percent of the milk production decrease. Heat-stressed cows become hypersensitive to insulin, which results in cows becoming dependent on glucose as their main source of energy. This, in turn, blocks the breakdown of fat stores, so heat-stressed cows cannot convert excess condition into energy. Therefore, it is very important to make proper adjustments to the ration to ensure dairy cows have access to enough energy to meet performance targets over the summer months.

It’s rare that we consider this but, in reality, summer months in Canada can span almost half of the year – from the end of May and extending into September in some regions. In addition, when heat-stressed cows use more glucose for energy, there is less glucose available to the mammary gland to make lactose, the key driver of milk volume.


Nutritional strategies to reduce negative effects

Nutritional adjustments serve as a security to reduce the negative impacts of heat stress when conditions are unavoidable. Let’s review some strategies that could help reduce the susceptibility of your herd to hot and humid conditions:

1. First and foremost, make sure cows have access to fresh water. Like humans, dairy cows exposed to high temperatures will feel the need to drink more water. Make sure there is enough water space to accommodate the size of the herd in the barn. Following the recommended guidelines from the Cow Signals Program, keep in mind the maximum distance a cow should have to walk to find fresh water in a freestall barn should not exceed 50 feet.

Also, barn design should allow a minimum of 3 to 4 linear inches of drinking water access per cow. In a tiestall barn, flow of water should reach a minimum of 16 litres per minute for individual water bowls. During summer months, optimal water flow should reach up to 20 litres per minute. In hot summer days, water requirements for dairy cows could easily attain 240 to 250 litres per day. Always keep in mind that water is non-negotiable for high-producing dairy cows.

2. Another, more creative nutritional adjustment that can be considered is the use of specific additives that can affect cellular hydration. This is a more abstract concept which can be explained by ways of osmosis. Water moves from a high-concentrated environment toward a less-concentrated environment.

As an example, if you separate two containers of water with a high concentration of salt and the other with a low concentration of salt with a semipermeable membrane in between, after some time, the level of water in the high concentration of salt container will be higher, and the concentration of salt in both containers would be the same (see Figure 2).

Osmosis concept


This is a natural biological process called osmosis.

How does this apply to the dairy cow? The answer is simple: Dehydration occurs when there is not enough water in the cow’s cells. Because of the heat, cows will lose a lot of water that is drawn out of their cells as part of the cow’s natural cooling system. This phenomenon is responsible for most of the animal’s heat stress symptoms. However, it is possible to draw some of this water back into the cells of the cow and reduce these symptoms with this osmosis concept.

By using specific ingredients designed to enter the cow cells and create a “less-concentrated” environment, cells will naturally draw water back in to equalize concentration between the outside and the inside of the cells, which will reduce the negative impact of the dehydration caused by excessive heat. This strategy has shown positive results in commercial dairy farms reducing the negative effect of heat stress on high-producing dairy cows.

3. An additional nutrition strategy is to stimulate the cow’s immune system and the cow’s ability to partition energy during these challenging periods. Heat stress affects the cow’s metabolic balance. Thus, the immune system consumes more energy (glucose) to fulfil its metabolic needs, energy which is taken away from the cow’s primary objective: milk production. To support the cow’s immune system, an efficient approach is to use bioactive metabolites that support the cow’s immunity by providing natural biological compounds involved in her normal metabolic responses. These bioactive molecules have demonstrated a positive impact on the immune response of cows during heat stress.


We cannot control the weather, and heat stress will undoubtably continue to present a large challenge to dairy operations. Despite optimal management and facility improvements for heat abatement strategies, on the hottest (and most humid) days, heat stress can still wreak havoc.

Nutritional changes like making sure the ration is properly balanced to meet our cows’ energy demand, providing fresh water, including a specific additive to improve hydration and stimulating the cows’ immune system are the most economical and efficient strategies to support high-producing dairy cows during heat stress challenges.  end mark

References omitted but are available upon request. Click here to email an editor.

Marc-Antoine Guesthier is the dairy technology development specialist with Cargill/Purina. Email Marc-Antoine Guesthier.