Feed Additives: A Necessary Tool for Overcoming Cow Heat Stress

As the summer months approach, it is time to start thinking about managing heat stress in lactating dairy cows. Every cow has a thermoneutral zone – a range of temperature in which she does not need to increase heat production or heat loss to maintain her body temperature. Heat stress occurs when a cow is pushed out of this zone due to a combination of high heat and humidity. This typically occurs when the temperature-humidity index exceeds 67.Dairy Cow Temperature Humidity Index THI

When a cow is heat stressed, a cascade of responses occur to help her maintain her core body temperature. This cascade of events leads to poor cow health, milk yield, growth, and reproduction.

Dairy cow heat stress response cascade


During a heat stress event, cows should have unlimited access to clean drinking water. The use of shade, fans, and sprinklers can also help the cow stay cool. However, even with these tools, cows may not be able to remain in the thermoneutral zone. Feed additives, such as exogenous enzymes, yeast cell wall, probiotic bacteria, live yeast, and yeast culture, are another tool that should be considered to help minimize the negative effects of the heat stress cascade.

A primary effect of heat stress in lactating dairy cows is their maintenance energy requirements increase to combat the heat. At the same time, their absorption of energy from the diet goes down due to reduced intake, poor rumen function, and loss of lower gut integrity.

Exogenous enzymes are a beneficial addition to the diets of heat stressed cows because they help the cow capture more dietary energy. They do this by physically binding to feed particles and helping to break them down. This leaves feed particles more accessible to rumen microbes and more available for absorption in the lower gut. Additionally, enzymes support rumen microbes by enhancing their attachment to feedstuffs, production of enzymes, and growth. All these actions support rumen function and allow the cow to extract more energy out of the diet.

Both live yeast and yeast culture further support rumen health. During heat stress, drooling and a reduction in rumination lead to less rumen buffering and low rumen pH. Both live yeast and yeast culture have been shown in a multitude of studies to increase rumen pH. Additionally, research has shown both yeast culture and live yeast support rumen microbial growth leading to improved feed digestion in the rumen and more rumen microbial protein, both of which provide additional energy and nutrients to the cow.

As shown in the cascade above, changes in blood flow leave the lower gut damaged and susceptible to opportunistic pathogens. These pathogens can put a strain on the immune system and compete for nutrients; both of which put the cow at increased risk for disease and low milk production.

The immune system requires large amounts of energy to function, so it’s activation during heat stress pulls energy away from heat dissipation and milk production and diverts it to immune function. Additionally, lower gut damage reduces nutrient absorption, compounding the lack of energy availability.

Yeast cell wall products and live probiotic bacteria are both great options to support pathogen inhibition, gut integrity, and immune function.

Research on yeast cell wall and live probiotic bacteria has consistently shown they inhibit pathogens. Yeast cell wall binds pathogens, such as E. coli and Salmonella, allowing them to be flushed out of the system without causing harm. Probiotic bacteria, on the other hand, have been demonstrated to outcompete pathogenic bacteria for nutrients in the gut, as well as produce antimicrobial compounds.

Probiotic bacteria also optimize tight junction protein function. Tight junction proteins help maintain intestinal integrity by preventing gaps from forming between gut cells thereby blocking pathogens and toxins from entering the blood stream.

Both probiotic bacteria and yeast cell wall also support the growth of commensal bacteria in the gut, which outcompete pathogens and enhance nutrient utilization by the cow.

Finally, these two additives are involved in immune system modulation. In a situation where the cow is facing an immune challenge, we would like to see her immune system respond quickly and appropriately to overcome the stressor and then quickly return to normal. Both probiotics and yeast cell wall support immune activation so she can respond more effectively to the challenges she is facing allowing for a quick recovery. Without these products in the diet, her immune system may function at a low-level long term without ever overcoming the pathogenic challenge. This would continually divert energy away from production and heat dissipation.

In summary, heat stress has a multitude of negative impacts on the cow that include poor rumen function, lower gut damage, and growth of opportunistic pathogens. This is compounded by low energy intake and absorption during a period of increased energy need. As a result, the cow exhibits poor health, milk production, reproduction, and growth. Feed additives are one solution to support her during this time of stress and help her get back to her normal, healthy self.

To learn more about Papillon’s prebiotic and probiotic technology, click here.



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