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Heat stress is a major concern in the management of dairy herds which adversely impacts welfare, performances and farm profitability. Moreover, considering the global climate change – with an estimated average rise of temperature on earth, between 0.5 to 4.8°C by 2100 – the heat stress episodes should become more common in farms.
To measure heat stress, the best indicator remains the Temperature and Humidity Index (THI). Dairy cows struggle with heat stress when THI rises above 72 units. This level is reached, for example, from a temperature of 24°C and a humidity of 68% (see graph1).
Graph1: Heat stress diagram for dairy cows, Burgos Zimbelman and Collier, 2011
Above a 72-THI, each unit of supplementary THI will cause a fall of 0.2kg of milk/cow.
In Northern Europe, heat stress situations may even occur below this gradient. For example, a recent study in Scotland following the performance levels of a dairy herd during several years shows a decrease in milk production from a 60-THI (Hill and Wall, 2014).
Multiple consequences of heat stress
Heat stress has different consequences on dairy cows:
- Above 71 °F (22°C), voluntary feed intake decreases, deteriorated by high humidity (table 1). To compensate this feed intake fall, there is an increase in body reserve mobilization.
|Feed Intake (%)||Relative Humidity (%)|
Table 1: Voluntary feed intake decreases with raising temperatures and humidity (Garcia and Diaz-Royon, South Dakota University, 2014).
- There is also a redistribution of blood to the periphery to maximize radiant heat dissipation, while vasoconstriction occurs in the gastrointestinal tract. As a result, the exchanges at intestinal level are impaired in both ways: there is less nutrient assimilation in blood and there are potential risks of damage of the intestinal barrier.
- Besides, panting increases heart rate and the excretion of carbonic gas. To maintain blood pH animal eliminates bicarbonates through kidney, leading to a metabolic acidosis. Moreover, the reduction of salivation increases the risk of acidosis.
- Another consequence is an important loss of electrolytes, through sweating.
- Several studies show an increase of the anoestrus period after calving, for dairy cows suffering from heat stress, largely due to a lack of energy intake.
- Heat stress during the dry period of dairy cows decreases calf birth weight and compromises the passive IgG transfer from colostrum and cell-mediated immune function of the calves during the pre-weaning period (Tao, 2012).
All these impacts are even amplified with high-potential animals, which are particularly sensitive to temperature and hygrometry variations.
Nutrition to fight heat stress impacts
Due to the wide variety of heat stress impacts, it is very difficult to solve it with a unique and single mode of action. Among the possible options, nutrition can play an important role.
The nutritional solution Axion®Thermoplus incorporated to feed was developed to act at the different levels impaired by hot weather in order to maintain animal performance, through three several ways:
- To prevent the feed intake drop, Axion®Thermoplus, as a specific blend of feed ingredients (with selected plant extracts and aroma), supports dry matter intake. In fact, its active components stimulate the activity of the key enzymes which contribute to feed digestibility (amylase, lipase, trypsine, and chymotrypsin).
- The management of the mineral fraction via the use of Axion®Thermoplus (DCAD, buffers) also contributes to boost the feed intake with a better balance of electrolytes needs. Plant extracts increase salivary production which gives supplementary help for buffering the diet.
- Plant extracts are also active in the general metabolism regulation, with a reduction of the heart rate and body temperature of the animals.
Field trial results
CCPA Group made several trials testing several diets and nutritional solutions, in different countries. In each country, an increase in milk production during hot period was seen for the batches of animals supplemented with Axion® Thermoplus: from 0.5 to 3 litres more, depending on different parameters. Even in farm with existing cooling system (for example in Viet Nam), a gain was seen with Axion® Thermoplus. In the following table are summarized several field trials led with two batches of animals, in different countries worldwide.
|Location||Number of animals||Cattle breed||THI||Milk –Control group||Milk – Axion® Thermoplus group||Difference||P-value|
|Viet Nam||178||Prim Holstein||82||24.2||25||+0.8||p<0.05|
|Viet Nam||39||Prim Holstein||82||24||25.05||+1.05||p<0.05|
Table 2: Improving milk yield during heat stress, CCPA Group, 2016
It is also possible to reduce the impact of heat stress for small ruminant production. Indeed, another test with goats leads to the same kind of results.
For fattening bulls, trials were also led in Brazil. These experiments have shown better performance levels and feed conversion rates with Axion® Thermoplus.
|Location||Number of animals||Weight at start (kg)||ADG –Control group||ADG Axion® Thermoplus group||FCR – Control group||FCR -Axion® Thermoplus group|
Table 3: Increasing growth during heat stress, CCPA Group, 2012
Of course, beside nutrition, it is strongly recommended to control and adapt housing conditions and cooling systems and to select the time of feed distribution.
In order to evaluate the risk level of heat stress in farms, CCPA GROUP has also developed for the producers a heat stress application for smartphones (Iphone and Android) entitled: ThermoTool™, which can be downloaded for free on Apple Store: https://itunes.apple.com/us/app/id981585161 and Google Play: https://play.google.com/store/apps/details?id=com.mobizel.thermotool. Thanks to this application, breeders can anticipate heat stress over 5 days and quickly adapt, if necessary, the management of their farm and the animal nutrition.
Ruminant Product Manager