You are viewing Asia Pacific


Why Does Heat Stress Matter on Dairy Cattle?

Heat stress is caused by a combination of weather and environmental variables, including high ambient temperature, humidity, solar radiation, and wind speed. Under high heat load, when the animal’s ability to dissipate body heat is impaired, additional body heat may be detrimental to the animal’s well-being, which leads to negative impacts on both animal welfare and the economic performance of production system.

The impact of heat stress is one of the costliest issues facing producers and has consistently been associated with:


Cows under heat stress will reduce dry matter intake (DMI) by 20% – 25%. As a result of the decreased DMI, cows enter negative energy balance (NEBAL), which can lead to losses in body weight (BW) and body condition score (BCS).


Temperature Humidity Index (THI) - Dairy

It was traditionally thought lactating cows become heat stressed when conditions exceed a temperature-humidity index (THI) of 72.1 However, recent climate-controlled experiments indicate milk yield starts to decrease at THI of 68. 2-4,6-7 The temperature humidity index chart examines the dairy cattle experience with heat stress under conditions that typically are not thought of as stressful and the consequences can be severe. (Figure 1)

Impact of heat stress on achieving pregnancy

The inability of a cow to dissipate heat effectively compromises its ability to function normally down to the molecular level. 4 The impact of heat stress can have both short-term and long-term consequences on reproduction depending on the stage of the reproduction cycle and the length of the heat stress event. 

Heat stress negatively impacts the ability of a cow to become pregnant through both internal and external controlled pathways. 


Some of the many pathways in which heat stress can lead to reduced fertility:

  • Reduced riding behaviour
  • Altered progesterone levels
  • Low calf birth weight
  • Short estrus duration
  • Altered Gonadotropin-Releasing Hormone (GnRH), Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH)
  • Reduced follicle quality
  • Reduced feed intake
  • Reduced estradiol
  • Altered cortisol levels
  • Increased early embryonic loss
Effect of chromium supplementation on heat stress

Kemin conducted a thorough meta-analysis of 16 peer-reviewed scientific journal articles that evaluate the impact of chromium supplementation in dairy cattle. The findings not only confirm the benefits of chromium but also provide a comprehensive statistical analysis of the advantages in production and profitability that dairy producers stand to gain.

Table 1: Summary of meta-analysis

Supplemental chromium impacts milk yield during heat stress

The influence of chromium on milk production has been attributed to its effects on energy metabolism reflected through decreased mobilization of NEFA from adipose tissue and increased insulin sensitivity. During extended periods of heat stress at different stages of lactation, increased glucose availability and utilization may have significant benefits to milk production. Research studies designed to test the effect of chromium on milk yield under heat stress conditions have shown cows supplemented with chromium yield more than control cows. 

Figure 2. Effect of chromium supplementation in lactating dairy cow diets on response in daily milk yield and dry matter intake, kg/h/d under heat stress conditions. (References are available upon request)

  • Dairy cattle have historically been selected for traits contributing to productivity. As a result of this selection strategy, dairy cattle have become less heat tolerant.
  • Keeping cows cool and eating are the two most important strategies for cows facing heat stress.
  • Multiple management and nutritional strategies are available to dairy producers to combat the heat.
  • Climate controlled experiments indicate milk yield starts to decrease at a THI of 68.
  • Kemin provides solutions for producers to help optimize animal performance.



Let's Work Together! Contact Us: Contact Us