A Hidden Danger: Heat Stress
April 14th 2021
One of the hidden problems in dairy farms is heat stress. It is usually ignored on the farms. However, its consequences are enormous and can severely affect the health of the farm’s herd and profitability.
What is Heat Stress?
Heat stress occurs when the body of the cow can not get rid of the excess heat. This is a severely dangerous medical condition and causes a decrease in milk production and several other diseases.
Heat stress causes low reproductive performance and low milk production in dairy cows. The sum of the external forces increases the animal's body temperature, respiratory rate, and sweating. It causes the excessive flow of energy (in the form of unabated heat) and in extreme cases, deaths may occur. Increased sitting time and decreased activity, hunger, thirst, low blood sugar, aggression, depression, skin tenting, lameness, decreasing body weight (12% loss of water) are observed for heat-stressed animals (Liam Polsky et al., 2017). Reduced estrous behavior is observed in heat-stressed dairy cows. (20-30% on summer days) (De Rensis and Scaramuzzi, 2003).
To avoid the problem of heat stress, modified drinking or feed intake is suggested (shifting feeding time to cooler periods) but these strategies are not enough to deal with heat stress.
In this period, the increase in ghrelin hormone (it is secreted when the stomach is empty) is observed more than in other times. Also, DMI (dry matter intake) is decreased, to reduce the effects of this; the concentration of diet is increased. High protein digestion causes increased urea in the animal. Therefore, rectal temperature is increased.
During heat stress, dairy cows are more strained than dry cows. In unfamiliar conditions, milk yield declines instantly. The number of necessary substances used for milk production decreases due to reduced DMI.
The Key Metric: THI
THI, an abbreviation of the Temperature Humidity Index, is the measure of the combined effect of environmental temperature and relative humidity on livestock. When THI exceeds 72, the effect of heat stress begins and after 78 THI it seriously affects the cows. When THI exceeds 82, it can cause significant losses in milk production and serious illnesses that can harm the cows’ long-term health.
Results of Heat Stress
Let's have a look at the results of heat stress from various researches:
|West 2003||Milk yield declined by 0.2 kg per unit increase in THI when THI exceeded 72. Another source says that it is 0.27 kg per THI after 72 (Cowley et al. 2015).|
|Summer et al. 2019||The daily milk yield is highly affected by climate change. The increment of temperature and humidity leads to a significant decrease in milk production (kilogram per day)|
|Nordlund et al. 2019||Heat load is recognized as having a substantial negative economic effect on the US dairy industry (St-Pierre et al., 2003), realized largely through reduced milk yield (West, 2003); impaired reproductive performance (Jordan, 2003; Schüller et al., 2016); and other losses associated with impaired mammary tissue function (Tao et al., 2018), adverse effects on the developing fetus during late gestation (Dahl et al., 2016)|
|St-Pierre et al., 2003||Heat stress results in total annual economic losses to the US livestock production industry ranging from $1.69 to 2.36 billion.|
|Mader et al., 2006||Excessive flow of energy (in the form of unabated heat) into the body, in addition to energy depletion required for lactation and growth, can lead to deteriorated living conditions, reduced quality of life, and, in extreme cases, death.|
|Keyserlingk et al., 2009||A lactating cow unable to seek shade on a hot day (natural living) will likely feel uncomfortably hot (affective state) and will experience reduced milk production.|
|NRC, 2001||Mild to severe heat stress can increase metabolic maintenance requirements by 7 to 25%, further exacerbating both the existing metabolic stress and the decrease in milk production.|
wiCow system has an environment sensor (climateSens) that continuously monitors the environment and notifies the users of problematic conditions. wiCow system tracks the core body temperature of cows quite accurately. In the field, our system encountered some heat stress cases. In those cases, our system detected the anomaly successfully and helped farmers to prevent possible negative damages.