Hot weather and post-weaning slump

Hot weather and calves don’t go together. Think of oil and water. Calves thrive in cool weather. Calves have a hard time coping with hot weather. They consider anything above 50° F warm. Weather above 70° is just plain hot for them.

Providing a Cooler Environment

If your calves are housed in a barn, the answer is ventilation. Fans, open curtain walls, natural convection are all ways to move air in barns.

If your calves are housed in hutches, be sure any vents built into the hutches are open. Some calf managers have situations where the backs of hutches can be raised a few inches to provide bedding-level ventilation.

Providing lots of clean water

Milk replacer does not provide adequate water for growing calves.Remember the 1 to 4 rule for water feeding. For each pound of dry matter fed, provide at least 4 pounds of water.

Older calves eating starter grain need plenty of clean water in order to efficiently convert feed into growth. In hot weather, even more water is used by calves in order to maintain normal body temperatures.

Free-choice water pays off in increased calf comfort, increased gains and improved health. But, unpalatable water doesn’t count as free choice water. Water containers need to be dumped frequently. Algae deposits grow quickly in hot weather and need to be scrubbed out of water pails.

Provide palatable starter grain

Begin with a good quality starter grain. Choose a grain with as low a rate of fines as you can afford. Try to get a starter grain with good pellet quality – look for a starter grain where most of the pellets are still intact after a day in a grain pail.

Remember, in hot weather fats in starter grains turn rancid very quickly. For the youngest calves I have always fed only a handful of starter and changed it daily. The purpose of renewing the grain daily for the youngest calves is to avoid the rancid smell. Also, this provides a fresh aroma that attracts calves.

Grain containers for older calves need daily attention, too. Even small amounts of liquid (water, milk, and urine) provide a favorable environment for mold growth. Calves seem to be quite sensitive to moldy odors. Fresh starter grain added on top of moldy grain often goes uneaten.

Avoiding Post-Weaning Slump

Providing all of the things mentioned above will help deal with hot weather stress. But, hot weather is still hot weather.

It’s almost inevitable that calves will respond to hot weather stress by beginning to eat starter grain at an older age than in cooler weather. In addition, they eat less grain per day at all stages of growth.

This delay and depression of grain intake may result in delayed rumen development. That is why careful weaning management is very important in hot weather months.

Step One: Close-up Cow Care: (See also the companion resource “Dry Cow Management Checklist)

Many calves get off to a poor start because of a weak link in colostrum management. An often-overlooked weakness in colostrum management is close-up cow care.

Close-up cow comfort and nutrition are especially important in hot weather. Two aspects of cow comfort that make a big difference are good ventilation and adequate space per cow. Keeping these cows eating enough is always a challenge.

Do they have enough space at the bunk (remember they are “super-size” mothers)? Is the feed bunk well- managed and free of spoiled and moldy feed? These last ten days before calving are the time when the colostrum is made. Close-up cow comfort and nutrition can make the difference between poor and good quality colostrum.

Step Two: Chronically Sick Calves:

Calves that get too little poor quality colostrum too late seem to get scours at the least little thing and often have to be treated for respiratory illness. They will need extra days to begin eating starter grain.

If chronically sick calves are observed carefully, you can delay their weaning until they have been consistently eating some grain for at least two weeks. These extra days before weaning will permit maturation of the rumen lining and walls. Then, when weaned, these calves will be able to adequately digest starter grain and absorb these nutrients.

Step Three: Strong Healthy Calves:

Even strong, healthy calves merit extra attention in hot weather. Many young calves spend more than eighty percent of their time lying down regardless of the weather.

This percentage of time lying down increases during hot daytime hours. When calves are resting they are not eating. In the summer, many calf managers observe the highest rates of starter grain intake are between 6 p.m. and 6 a.m. That’s when the calves are up and more active.

This means that calf managers need to take extra care to see that calves have adequate supplies of both starter grain and water at night. Promoting earlier and greater starter grain consumption pays off in decreased post-weaning slump.

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Sam Leadley

Sam Leadley
62 articles

Consultant on Calf/Heifer Management at Attica Veterinary Associates.

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Attica Veterinary Associates

Attica Veterinary Associates

Attica Veterinary Associates provide veterinary services and products, independent consultation in dairy management, nutrition and performance, and trainings.

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