Part Two: Feeding Through the Heat — Practical Nutrition and Management Changes That Work

By Dr. Tricia Wood, Technical Services-Ruminant, Lallemand Animal Nutrition

This article is the second in a series of three about heat stress in dairy cattle.

As temperatures climb, dairy cows face more than discomfort. Heat stress has a profound physiological impact on rumen function, nutrient utilization and milk production. While many farms focus on environmental cooling systems, optimizing nutritional strategies is equally essential for supporting herd health, production and profitability during extended periods of elevated heat and humidity.

Cows begin experiencing the negative effects of heat stress at a temperature-humidity index (THI) of just 68.¹ As respiration rates climb, bicarbonate is diverted from the rumen to the blood to stabilize acid-base balance.² Coupled with reduced rumination and saliva production, this leaves cows vulnerable to sub-acute ruminal acidosis (SARA), lowered dry matter intake (DMI), and reduced milk and component yield.³ Proactive, research-based nutrition adjustments can help maintain productivity and cow well-being during heat events.

Here are 10 practical, actionable tips to help cows power through the heat:

1. Feed highly digestible, well-fermented forages with elevated neutral detergent fiber digestibility (NDFd).
Limit undigestible fiber while ensuring enough effective fiber to stimulate cud chewing and natural rumen buffering — without adding excessive metabolic heat load.⁴

2. Regularly analyze silage quality and monitor inventory.
As starch digestibility increases with storage time, routinely evaluate starch and NDF digestibility with a forage analysis laboratory and work with your nutritionist to fine-tune ration formulations, particularly to avoid excessive rapidly fermentable carbohydrates.⁵

3. Support rumen digestion with a proven active dry yeast probiotic (ADY).
Saccharomyces cerevisiae CNCM I-1077 is an ADY that is supported by over 25 years of research to balance rumen pH, improve fiber digestibility, and reduce lactate — helping cows get more out of each pound of feed.^6,7,8

4. Balance dietary cation-anion difference (DCAD) using sodium bicarbonate and potassium carbonate.
Supporting acid-base balance with proper DCAD buffers helps maintain rumen stability under heat stress.²

5. Adjust feeding schedule.
Encouraging intake when cows are naturally more comfortable helps support consistent dry matter intake and overall performance. Feed during cooler times of the day and manage TMR delivery timing to minimize sorting and spoilage.

6. Perform frequent TMR push-up.
Keep fresh, cool feed in front of cows and reduce ration sorting by moving feed up to the bunk several times throughout the day.

7. Monitor TMR moisture and particle size
Optimize palatability and limit sorting by adjusting TMR moisture and verifying particle distribution. Regular on-farm evaluations, supported by Lallemand’s expert team of field specialists and technical support, can help identify ration inconsistencies and provide tailored recommendations to support intake and rumen function.

8. Use a silage inoculant with proven aerobic stability benefits.
Inoculants that include Lactobacillus hilgardii CNCM I-4785 in combination with L. buchneri NCIMB 40788 and Pediococcus pentosaceus NCIMB 12455 improve bunk-life stability, reducing heating and spoilage during warm weather.⁵

9. Provide unrestricted access to clean, cool water.
Ensure water sources are clean, freely flowing, and strategically placed near feed bunks, holding pens, and return alleys. Water is the most important nutrient and the key to supporting rumen function and thermoregulation during heat challenges.

10. Maintain and monitor heat abatement equipment.
Confirm that fans, misters, and other cooling systems are functioning efficiently and correctly directed. Misters should not be aimed toward the feed bunk, as excess moisture can accelerate heating and spoilage in the TMR.

Key Takeaways
Smart, timely nutrition adjustments, paired with attentive feeding management, give producers critical tools to maintain DMI, rumen health, and milk production through warm and humid weather. By integrating these practical, research-supported feeding and management adjustments, producers can build a comprehensive heat stress mitigation strategy that sustains rumen health, preserves milk and component yield, and protects cow comfort during even the most challenging summer months.

However, no nutritional strategy can fully compensate for poor barn climate management. Effective heat abatement practices not only improve immediate cow comfort but also reduce the cumulative financial losses associated with heat stress across the lactating, dry, and transition pens.

Do you know how your environmental heat abatement strategies stack up? Read Part 3 —Setting Your Cows Up for Success — Heat Abatement Strategies That Are Worth It

References:
1 Collier, R.J. et al. (2012). Quantifying heat stress and its impact on metabolism and performance. Proc. 23rd Florida Ruminant Nutrition Symposium.
2 Baumgard, L.H., et al. (2014). Feeding and managing cows to minimize heat stress. Tri-State Nutrition Conference.
³ Mishra, M. et al. (1970). Effect of diet and ambient temp-humidity on ruminal pH, oxidation-reduction potential, ammonia, and lactic acid in lactating dairy cows. J. Anim. Sci., 30:1023-1028.
4 Baumgard, L.H. & Rhoads, R.P. (2012). Ruminant production and metabolic responses to heat stress. J. Anim. Sci., 90(6):1855-1865.
5 Ferraretto, L. et al. (2014). Influence of ensiling on the digestibility of whole-plant corn silage.
6 Marsola, R.S., et al. (2010). Effect of feeding live yeast on performance of Holstein dairy cows during summer. J. Dairy Sci.
7 Bach, A. et al. (2007). Daily rumen pH pattern of loose-housed dairy cattle as affected by feeding pattern and live yeast supplementation. Anim. Feed Sci. Technol., 136:146-153.
⁸ Bittencourt, L.L. et al. (2008). Responses of lactating dairy cows to the supplementation with live yeast. J. Dairy Sci., 91(E-Suppl. 1).