When temperatures rise, dairy cattle feel the heat — literally. Even mild temperatures can take a toll on their health, milk production and overall performance. Recognizing the warning signs and taking proactive steps can make a difference in keeping your herd cool and comfortable.
The warning signs of heat stress
Heat stress can be identified through both direct observation and measurement. One clear indicator is elevated skin temperature, which can be measured with an infrared thermometer. A skin temperature reading exceeding 96.5 F at the top of the rear udder attachment suggests heat stress. Increased respiration rate — above 60 breaths per minute — is another warning sign.
Behavioral changes also provide clues. Heat-stressed cows often stand rather than lie down, increasing the risk of lameness. They also gather around water sources and darker/shadier areas of the barn despite the crowding which increases the localized temperature.
Impact on milk production and herd health
Heat stress reduces dry matter intake (DMI), leading to lower energy for milk production. This accounts for a significant portion of milk yield losses. Additionally, heat stress affects digestion and nutrient absorption, further reducing productivity.
Physiological changes, including immune system activation, also can contribute to production declines. Heat stress can begin at a THI (temperature humidity index) of 68°F, especially for high-producing cows because increased metabolism generates more internal heat.
Heat stress management checklist
To reduce the effects of heat stress, producers can follow these key strategies:
☐ Provide adequate water access: Ensure cows have unrestricted access to clean, fresh water with 3 inches of water spaces per cow.
☐ Clean and service fans for air movement: Misters may also help in conjunction with fans in some environments.
☐ Prevent overcrowding: Pay particular attention to minimizing time in the holding area before the parlor.
☐ Optimize nutrition:
- Evaluate trace mineral levels like zinc for skin integrity, which can support hoof durability and intestinal lining.
- To compensate for lower intakes, use palatable energy sources and the most highly digestible forages available during hotter months.
- Add live yeast and buffers to support rumen function, as excessive drooling and panting reduce buffering capacity.
☐ Use barn curtains: Adjust barn curtains to block the sun or add shades to encourage cows to spread out.
Heat stress management starts early
One of the most effective interventions is monitoring heat stress in dry cows before the pre-fresh period. Research shows that cows exposed to heat stress during late pregnancy produce less milk in the subsequent lactation1, and their offspring may have lower milk production over three lactations2. Consequently, addressing heat stress can support current milk yield but may also aid in generational improvements.
By implementing these strategies, dairy producers can minimize the risk of losses, optimize herd health and help sustain productivity throughout hot weather. Producers looking for additional insight on heat stress management should contact their trusted Fortiva representative.
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References
1 Fabris T. F., Laporta J., Skibiel A. L., Corra F. N., Senn B. D., Wohlgemuth S. E. and Dahl G. E. Effect of heat stress during early, late and entire dry period on dairy cattle. J. Anim. Sci. 2019; 102:5647-15721.
2 Laporta J., Ferreira F. C., Ouellet V., Dado-Senn B., Almeida A. K., De Vries A. and Dahl G. E. Late-gestation heat stress impairs daughter and granddaughter lifetime performance. J. Anim. Sci. 2020; 103:7555-7568.
