How to reduce its negative effect on milk production.

We define heat stress as the animal’s inability to lower its body temperature when the effective ambient temperature exceeds comfort conditions.

What causes heat stress?

1. Decreases dry matter intake. Thus, for example, at 35º C, the voluntary consumption of dry matter can be 15% lower than what the cow would have at 20º C.
2. Increases energy needs for maintenance. At 35º C, a cow would need a dry matter intake 10% higher than what it would need at 20º C to maintain the same milk production.
3. Decreases the synthesis and release of thyroid hormones, which have a very important function in milk production.
4. Conception rates decrease from 40% to less than 10%.
5. Increases the interval between births and discards due to sterility.

The dairy cow has a “thermo-neutral zone,” that is, a range of temperatures in which maximum comfort and optimal productivity are achieved. This temperature ranges from 4º to 20-25º C. Above 25ºC, heat stress begins to occur.

A THI greater than 72 affects the well-being of dairy cows. The relative humidity of the air must be taken into account. The combination of high temperatures and environmental humidity make up the so-called THI (Temperature and Humidity Index), a measure used to consider heat stress.

Prevention measures

With high temperatures, a high-production cow consumes up to 140 liters per day, so the availability of good quality water is essential.

• Adult cattle consume 8-10% of their weight.
• High temperatures increase water requirements between 30 and 60%.
• 50% of a cow’s water consumption occurs during the two hours after milking.

Shade is essential to ensure the comfort of cows and adequate food consumption. Likewise, the installation of ventilation systems or water sprinklers can be useful. In the shade, a cow can lose up to 50% of the heat.

1. Adapt milking schedules. Especially if the facilities are deficient and milking times are prolonged.
2. Avoid long walks during the times of day with the highest THI (greatest stress).
3. Manage grazing in the moments with the lowest daily THI (afternoon/night).
4. Provide quality water in sufficient quantities and in strategic places, which allow easy, quick and comfortable access to the animals. 5- Natural and/or artificial shade in the waiting pen, paddocks and animal confinement areas. 6-Implement ventilation and spraying systems together with shade: it consists of applying consecutive cycles of water spraying and forced ventilation on the cows, in the waiting pen and in the food supply sector.

The use of ventilation and spraying prior to milking allows to increase milk production between 5% and 15% when the THI was higher than the comfort threshold of 72. (Ghiano, 2012).
| Med. Vet Roberto Vaca