Howard Jensen, DVM, MS, ACAN
Heat stress is just around the corner and despite the advances in environmental cooling, it continues to cost the dairy industry millions of dollars every year.
The negative impacts of heat stress include:
- decreased milk production
- increased metabolic disorders
- compromised milk components
- reduced reproductive performance
- slowed growth
- rumen acidosis
- cow death
The cow responds to heat stress with:
- drooling and sweating
- circulatory adjustments
- endocrine changes
- altered eating patterns, including decreased feed intake
- panting and an increased respiratory rate
What are the effects of the cow’s response to heat stress on rumen function?
Panting increases respiration rate, which sets off a negative chain of events. An increased respiration rate causes more CO2 to be exhaled which decreases CO2 in the blood stream. Because the buffering mechanism of blood requires a 20:1 HCO3 (bicarbonate) to CO2 ratio, when more CO2 is lost through an increased respiration rate, the kidneys secrete HCO3 in order to maintain the proper ratio.
This increased HCO3 secretion reduces HCO3 concentration in the saliva, which lowers the saliva’s buffering capacity. The combination of drooling (decreasing the quantity of saliva entering the rumen) and saliva with less buffering capacity gives us cows with lowered rumen pH. This coupled with the altered eating patterns of slug feeding and sorting, all predisposes the heat-stressed cow to acidosis.
Research by the University of Arizona and others has done a lot to explain how the cow reacts metabolically during heat stress. Experiments with cows under heat stress compared to thermal neutral pair fed cows suggest that during heat stress there is increased sensitivity to insulin. Therefore, the heat stressed cow does not mobilize NEFA’s for an energy source like what might have been previously thought. This information suggests that maximizing glucose production may be important in minimizing the nutrient shift. The real issue is the lack of energy to produce milk and maintain body condition.
The extra requirement for energy could come from dietary fat, increased glucose or increased VFA production. Because propionate is gluconeogenic, increasing propionate has been suggested as one possible solution. But increasing propionate by increasing starch in the diet could be counterproductive. Increased starch in the diet combined with sorting can lead to further problems due to a rumen pH that is already compromised. Increasing propionate/glucose could also have a negative effect on the satiety center, actually decrease intake and possibly make the negative energy balance worse. However, increasing acetate from increased fiber digestion could provide energy without a negative effect on intake or rumen health.
Where does Amaferm fit into heat stress management?
Amaferm works best when energy is limited.
Amaferm increases digestion and helps to stabilize rumen pH, thus supplying the additional energy needed to meet the demands associated with increased maintenance requirements caused by heat stress.
Research trials with Amaferm experiencing heat stress show that Amaferm fed cows:
- Consumed more feed
- Higher water intakes
- Lower body temperature
- Produced more milk
Milk production is not only lost during the heat insult, but continues following heat alleviation. Ominski et al., 2002 showed that even short-term heat stress will negatively affect future milk production. Following heat insults, the cow may repartition nutrients to rebuild tissues that were mobilized to meet increased energy demands – further delaying the return to normal milk production.
- Amaferm can help shorten this future loss of milk production following heat stress because of the increased nutrients available to the cow during heat stress.
Amaferm research (Chiou et al., 2002 shown below) conducted during the Spring/Summer months of May-July showed that cows fed Amaferm actually increased body weight (1.75 lbs/day). The Amaferm-fed cows partitioned the extra nutrients from increased ruminal digestion for body condition instead of milk production.
SARA (sub-acute rumen acidosis) is frequently a complication associated with heat stress due to sorting, saliva loss and a loss in the saliva’s buffering capability. Amaferm stimulates both of the major lactate fermenting bacteria, which will help stabilize the rumen pH.