Managing heat stress in dairy cows to maintain production

Dairy farmers know the importance of keeping their cows cool and comfortable. Unfortunately heat stress isn’t just a threat in scorching deserts – even moderate climates can bring periods of discomfort for a herd. Heat stress in dairy cows is a significant issue that affects their productivity and overall health. It is essential for dairy farmers to manage heat stress effectively to ensure optimal milk production and longevity of their herds. Here is what you need to know to keep cows cool and productive during warm seasons.

People might think heat stress is only a concern in hot, dry areas. However, dairy cows in moderate climates like Europe and coastal areas of Latin America and North America can also suffer from heat stress during warm and humid periods. While cows can develop some tolerance to heat stress with regular exposure, those in moderate climates may struggle to adapt quickly to sudden spikes in temperature. Climate change has made heat stress a more frequent issue globally.

The key to preventing heat stress lies in understanding how cows regulate their body temperature. Unlike humans who can sweat freely, cows rely on panting and increased respiration to cool down. This process comes at a cost – reduced feed intake, digestive issues, and ultimately, a drop in milk production.

RECOGNIZING THE SIGNS EARLY
Dairy cows strive to keep their body temperature between 38-39ºC (100-102ºF). Unlike other species, they produce a significant amount of heat through metabolic processes, especially during the microbial fermentation of feed in the rumen. A highly productive dairy cow generates even more metabolic heat, making them more susceptible to heat stress. Rising global temperatures and increased milk production have led to longer periods where cows exceed their heat load capacity, resulting in heat stress.

Look for these clinical signs of heat stress in your cows:
• Panting
• Drooling
• Milk leakage
• Reduced milk production
• Prolonged standing

The Temperature Humidity Index (THI) is a common method for quantifying the risk of heat stress by combining environmental temperature and humidity (Figure 1). While threshold values often reference cows acclimatized to high temperatures, in temperate regions, cows can show signs of heat stress at lower THI levels, around 62. THI does not account for radiation, making it more suitable for housed dairy cattle rather than those grazing in direct sunlight.

The Dairy Heat Load Index (DHLI) is a relatively new index used to assess the risk of heat stress in dairy cows. It’s designed to be a more suitable predicter for grazing cattle. The DHLI uses humidity and temperature measurements from a “black globe” placed where the cattle graze, providing a more accurate assessment of the conditions cows face.

WHY DOES HEAT STRESS IMPACT SUSTAINABLE DAIRY FARMING?
Increasing the Lifetime Daily Yield (LDY), (the average production per day from birth to culling), is crucial for sustainable dairy farming. LDY is influenced by milk production per lactation and the number of lactations per cow. Heat stress can lead to systemic immune activation and inflammation, which negatively impacts both. While systemic immune activation often occurs around the transition to lactation, heat stress can happen at any time, exacerbating the problem.

When cows experience heat stress, they try to cool themselves by reducing their dry matter intake (DMI), redirecting blood flow to their skin, and increasing evaporation through sweating and panting.

This cooling response leads to several issues:
• Reduced Nutrient Intake: Lower DMI means fewer nutrients for milk production.
• Gut Integrity: Reduced blood flow to the intestines can cause “leaky gut”, leading to systemic immune activation and inflammation.
• Respiratory Alkalosis: Panting decreases blood CO₂ levels, increasing blood pH and causing rumen acidosis, further exacerbated by saliva loss.

Heat stress also negatively affects cow fertility. Elevated body temperatures can impair oocyte quality, embryonic growth, and overall reproductive function. Additionally, heat-stressed cows may show reduced signs of estrus due to lethargy.

MANAGING HEAT STRESS EFFECTIVELY: MITIGATING ACTIONS
Cows lose heat through radiation, convection, conduction, and evaporation. If these methods are insufficient, cows will start panting and sweating. However, cows have a low sweating rate, and high humidity can reduce the effectiveness of evaporation. Increased water consumption is crucial, but severe heat stress may cause cows to stop drinking, leading to dehydration and other health issues. Advice is to implement heat stress management programs about three weeks before cows are expected to experience heat stress. This proactive approach allows cows to adjust, minimizing the adverse effects on their health and productivity.

Effective heat stress management involves both managerial and nutritional strategies:
Managerial Strategies:
• Provide Shade: Ensure all cows have access to shade to increase rumination and milk yield while decreasing body temperature.
• Ensure Adequate Water Supply: Increase water points and ensure high-quality water is available. Chilled water can further help in reducing heat stress.
• Enhance Ventilation: Improve barn ventilation to keep the temperature close to outside levels, enhance convectional heat loss, and remove humid air.
• Use Evaporative Cooling: Utilize cooling pads or atomizing nozzles along with strong ventilation to reduce barn temperature without increasing humidity.
• Sprinkling: Sprinkling cows with cold water can be effective but requires large amounts of water and might lead to avoidance behavior if not managed well.
• Maintain Bedding and Flooring: High-quality bedding and flooring can reduce the risk of lameness and encourage cows to lie down.

Nutritional Strategies:
• Adjust Feeding Times: Feed cows earlier in the morning and later in the afternoon to align peak heat load with cooler parts of the day.
• Increase Diet Energy Density: Substitute roughages with concentrates to increase energy density and compensate for reduced DMI, though this needs careful balancing to avoid rumen pH issues.
• Prevent Feed Heating: Add substances to inhibit microbial growth in feed, ensuring it remains appealing and reduces reluctance to eat.
• Provide Nutritional Supplements: Use buffers to stabilize rumen pH, increase DCAD, and add prebiotics and probiotics to support gut health and immune function. Prebiotics and probiotics such as Selko® LactiBute® to improve gut integrity, to reduce the risk of hindgut acidosis and to support the cow’s immune system. This can help to mitigate the negative effects from heat stress on dairy performance (Figure 2). Zinc supplements can help reduce the impact of heat stress on gut integrity and immune response ^7,8. Its mechanism of action includes upregulation of tight junction proteins between intestinal cells, enhancing epithelium repair and immune modulation ^2,3,4,5. On the other hand, excessive supplementation of minerals represents an environmental concern due to excretion in manure and can have a negative impact on fibre digestibility. Alternative mineral sources, like Selko® IntelliBond® Z represent an opportunity to optimize performance of dairy cows suffering from heat stress⁵.

Managing heat stress is critical for maintaining dairy cow productivity and health. By implementing effective managerial and nutritional strategies, dairy farmers can create a more comfortable environment for their cows during hot weather, minimize the negative impacts of heat stress, and ensure optimal milk production and herd health.

References:
¹Hammami H., J. Bormann, N. M’hamdi, H.H. Montaldo, N. Gengler. (2013) Evaluation of heat stress effects on production traits and somatic cell score of Holsteins in a temperate environment. J Dairy Sci. 96: 1844–1855.
²Murphy M.R., C.L. Davis, G.C. McCoy (1983) Factors Affecting Water Consumption by Holstein Cows in Early Lactation. J. Dairy Sci. 66: 35–38.
³Gorniak, T, Meyer, U, Südekum, K, and S. Dänicke (2014), Impact of mild heat stress on dry matter intake, milk yield and milk composition in mid-lactation Holstein dairy cows in a temperate climate. Arch. Anim Nutr. 68(5):358-69.
⁴Thompson I.M., A P Alves Monteiro, G E Dahl, S Tao, B M Ahmed (2014) Impact of dry period heat stress on milk yield, reproductive performance and health of dairy cows ADSA-ASAS-CSAS Joint Annual Meeting Kansas, USA.
⁵Habeeb, A.A, Gad, A.E, and M. A, Atta (2018) Temperature-Humidity Indices as Indicators to Heat Stress of Climatic Conditions with Relation to Production and Reproduction of Farm Animals. International Journal of Biotechnology and Recent Advances. 1(1): 35-50.
⁶Hansen, P.J. and C. F. Areéchiga (1999). Strategies for managing reproduction in the heat-stressed dairy cow. J. An. Sci. 77:2 36–50.
⁷Weng, X., A. P. A. Monteiro, J. Guo, C. Li, R. M. Orellana, T. N. Marins, J. K. Bernard, D. J. Tomlinson, J. M. DeFrain, S. E. Wohlgemuth, (2018). Effects of heat stress and dietary zinc source on performance and mammary epithelial integrity of lactating dairy cows. J. Dairy Sci. 101:2617–2630.
⁸Response of lactating dairy cows fed different supplemental zinc sources with and without evaporative cooling to intramammary lipopolysaccharide infusion: metabolite and mineral profiles in blood and milk (2020). Marins, T.N, Monteiro, A.P.A, Weng, X, Guo, J, Orellana Rivas, R.M, Bernard, J.K, Tomlinson, D.L, DeFrain, J.M. and S. Tao.J. Animal Scie, 2020, 98:10, 1–7.

About Lonneke Jansen
Lonneke Jansen, holds a MSc in Animal Sciences. Jansen is currently serving as Technical Commercial Manager Ruminants at Trouw Nutrition, specifically within the Selko Feed Additives department. Every Selko Feed Additive and every service related to a Selko Feed Additive is designed to enhance the sustainability of dairy farming by minimizing environmental impact, ensuring animal welfare and health, and providing farmers with a stable income.