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Understanding and Mitigating Heat Stress in Young Dairy Animals

July 9, 2018

We often don’t focus as much on heat stress in young dairy calves and tend to focus more on cold stress. However, it is just as important and producers or calf raisers should have a plan in place to help mitigate heat stress in these animals also. Why is it important? When calves are hot they eat less under stress which affects weight gains and overall performance and health. A study by Heinrichs et al. 2005, made the association between heat stress and subsequent first lactation cows finding that the calves that underwent heat stress early in life had a higher average age at first lactation. This obviously, affects the total cost of raising a heifer and a producers’ profitability.

The thermoneutral zone is a range of temperature in which animals perform best by maintaining a constant body temperature while not expending extra energy to do so. The temperature in this zone is not affected solely by the outside temperature but can be influenced by relative humidity, air movement, moisture, hair coat, sunlight (direct vs indirect), bedding, and rumination in older calves. It is important to remember that calves can often deal with heat better than cows simply because of their larger surface area in comparison to their weight and the fact that they are producing less heat due to minimal rumination occurring. Minimal research regarding the THI (temperature humidity index) for dairy calves has been done. The Temperature Humidity Index (THI) is a measurement that accounts for the combined effects of environmental temperature and relative humidity. When we look at the THI levels for lactating cows mild heat stress starts occurring between 68-71 THI index and a lactating cow will experience mild to moderate stress with a 72-79 THI index. This information can be found in the Dairy Heat Stress Management and Energy Use Planning Guide.

Thus, we need to be cognizant of the observable symptoms of heat stress in young dairy animals which are the following:

  • A calf’s body temperature will increase above 103 ˚F
  • There will be an increased respiration rate
  • There will be a loss of appetite
  • A decrease in activity
  • If dehydration in occurring due to heat stress there will be less urine output and manure will become firmer
  • There will be increased water consumption

Producers need to start mitigating heat stress even before the calf is born by looking to the dry cows. Keeping them cool is essential to helping maintain colostrum quality which often goes down in the summer. Thus, extra effort needs to be given to monitoring colostrum quality and possibly utilizing a colostrum replacer if necessary.

Maternity pen areas will need to be cleaned more often or if bed packs are used, fresh clean bedding added more often. With increased heat and moisture these become ideal pathogen breeding grounds.

If a calf is born and is extremely hot, they may need to be cooled down in high THI conditions. Utilizing fans will help this situation.

Do not forget to pay attention to how the animals are being transported and arriving at the calf raising facility. Does your trailer have enough ventilation to keep the calves cool? Are calves being checked for heat stress and given proper fluids upon arrival?

Are you adjusting the times at which you process calves (vaccinations and dehorning) and doing it in the cooler periods of the day? This will also decrease heat stress on the calves as well as humans.

Nutritionally, we need to remember a few key things with unweaned calves and heat stress. Calf starter intakes often decrease, while their energy requirements for maintenance will increase 20-30% when enduring heat stress. Thus, you will want to evaluate your milk replacer program along with considering increasing the amount times calves are fed milk or milk replacer daily from 2X/day to 3x/day. Additionally, offering smaller amounts of fresh calf starter more often will decrease spoilage and help intakes. A lot of FRESH, CLEAN, COOL WATER is an absolute must several times throughout the day if needed. Healthy calves will drink between 6 to 12 quarts of water daily and sick calves experiencing heat stress can drink up to 20 quarts of water. For more information on dehydration refer to the article, Recognizing Signs of Calf Dehydration. Additionally, you may have to extend weaning times by a week or more depending upon starter consumption during heat stress.

As we look to housing and ventilation keeping shade, airflow and cleanliness as priorities is a necessity.

Calves that are raised in hutches should have the opening to the north with all vents open during the summer months. Place them 4 feet apart and 10 feet between rows in the summer. A cement block can be placed under the back of the hutch to allow for a 6-8 inch opening to help create an upward draft forcing hot air out. Utilizing a shade cloth 4 feet above hutches will also help decrease the temperature in the hutches 3-4 ˚F if plastic hutches are utilized.

Calves raised in naturally ventilated barns will need increased air flow either by adding more fans or by using a positive pressure tube ventilation system. If curtain barns are utilized all curtain sidewalls should be completely open if the THI reaches 72.

Keeping calf housing clean is always essential and in the heat of the summer calf raisers need to be even more vigilant due to the ideal growth environment for pathogens. You may want to consider switching to inorganic bedding in the summer to help calves stay cooler, as sand absorbs more body heat rather than retaining it. Saw dust is also a consideration and does not retain as much heat as straw. The priority is keeping it clean, regardless of bedding used. Cleaning and disinfecting hutches or pens, bottles, nipples, pails and feeding equipment on a regular basis, while allowing for adequate drying time will help decrease bacteria, parasite and other micro-organism growth.

Making fly control a priority is also essential to helping mitigate additional stress placed on the animal through irritation caused by biting and disease transfer. Horn fly populations will peak in the hottest months and have a life cycle of 10-20 days which decreases with warmer temperatures. Face flies spread the pink eye bacteria by feeding on the protein found in eye mucus. Thus, keeping eye irritations such as blowing dust and debris to a minimum will help minimize pink eye infections.

Making heat stress management a priority in young dairy animals will pay off in years to come by improving the overall performance and health of the animal, while also impacting your profitability.

Source: Tracey Erickson, iGrow