With current elevated temps, it is a critical time to review different nutritional strategies for managing summer heat stress. At a temperature-humidity index (THI) of 68°F or above, cows will show they feel the elevated temps -- intakes decrease, meal patterns change, and metabolism and energy requirements are significantly altered. To combat this, certain nutritional strategies can be implemented to reduce the effect of heat stress and help maintain productivity.
Energy Density and Dry Matter Intake
One of the most impactful changes in heat-stressed cows is the reduction in dry matter intake. To compensate for this, we can alter diet formulation to increase overall energy density to offset the reduction in intake. Our goal is to maintain the number of calories consumed each day, despite the loss in dry matter intake. This can be achieved through feeding more digestible fiber, bypass fats, and/or starch sources.
Additionally, cows will reduce their overall number of meals and increase their meal size. With the change in meal behavior, using starch sources to increase the energy density of the ration may be discouraged due to the increased risk for unfavorable rumen conditions. Knowing this, utilizing digestible fiber sources such as high-quality forages or non-forage fiber sources would be the preferred route for maintaining favorable rumen conditions while driving energy density during heat stress. In addition to increasing carbohydrate sources, providing more rumen-undegradable protein (RUP) sources can help improve amino acid availability during time of reduced intake.
Feed Additives and Supplements
Due to increased sweating and respiration under heat stress, cows lose significant amounts of sodium, potassium, and bicarbonate. Supplementing the diet with additional electrolytes, via raising the dietary DCAD via potassium and sodium bicarbonate, can help maintain acid-base balance and improve hydration status. The positive relationship of raising the dietary DCAD on dry matter intake and performance was summarized in a meta-analysis by Iwaniuk and Erdman, 2015. Other additives that do not affect dietary DCAD and still combat summer heat stress effects would be osmolytes, vasodilators, and antioxidants. These products improve nutrient utilization and support thermoregulation.
Management Strategies
I would be remiss to not mention that cooling practices/systems are a critical part of reducing summer heat stress. Simply, barns with ample fans and sprinklers will have a greater impact on mitigating heat stress than any dietary strategy. In addition to cooling systems, managing the other resources is critical. Increasing access to clean water space and maintaining optimal feed availability via more frequent feed push-ups will help counteract decreased intakes and altered meal patterns.
Consider The Options
There are several options when it comes to reducing the effects of summer heat stress. By increasing energy density, adjusting carbohydrate and protein sources, and utilizing certain feed additives, producers can help maintain productivity. With the current elevated temperatures, now is the time to implement these strategies.
Your Next Read: Stop the Summer Surge: How to Keep Your SCC in Check
