Friday, March 29, 2024

Keep cool and don’t stress

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When you’re out in the sunshine this summer enjoying the warmer temperatures, spare a thought for the humble dairy cow, which is less able to vocalise her struggle out in the heat. Karin Schütz, senior researcher at AgResearch, says everyone can do something to ease the effects of the heat on their cows.
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Although the effects of heat stress are more severe in hotter climates such as parts of the United States and Australia, it is still an issue for many areas of New Zealand, particularly with the effects of El Nino starting to show.

Sometimes referred to as hyperthermia, heat stress is when a cow’s heat load is greater than her capacity to lose heat, ie her body is absorbing more heat than it dissipates.

“It’s caused by a combination of environmental factors like air temperature, humidity, solar radiation and air movement as well as animal factors like feed type, breed, age, coat colour and production.”

Although the response to heat stress differs from cow to cow, high-producing cows are more affected than lower-producing cows because of greater metabolic activity, a process which produces body heat. Black cows are more susceptible because they absorb the heat quicker. However, they are also able to lose that heat quicker. Older cows are also more at risk.

“One of the key issues going on is humidity. It decreases evaporation and reduces the cows’ ability to lose heat by sweating and breathing.”

Symptoms of heat stress are easy to spot and often occur in progression, from seeking shade and water to standing up to increase air flow around their body, crowding together, refusing to lie down to standing in or next to water, and a fast breathing rate.

“These are natural responses to warmer temperatures. When these responses fail and her heat load exceeds her ability to lose that heat, that’s when heat stress sets in.”

When air temperatures hit about 21C and relative humidity is at about 75% cows begin to experience a heat-induced depression of feed intake and lowered productivity. It is estimated that with each 0.5C increase in body temperature above 38.6C, milk yield will decrease by 1.8kg a day (15g milksolids/cow/day). There will also be changes in milk composition, with the percentage of fat and protein declining. Blood hormone concentrations also change.

“As heat stress becomes more severe cows will start open-mouth panting and drooling and that’s when you know they are in trouble.”

Schütz says when cows are really in trouble, simply hosing them down in the dairy can make a big difference but prevention is always better.

“Although we don’t have cows dying from heat stress here it’s still an issue, so things like minimising walking distances, walking them slowly and providing adequate shade and water are really important. A lactating dairy cow can require more than 100 litres/day which is quite a lot. So we are also looking at the viability of having an extra water trough in the exit race from the milking shed.”

Agresearch has researched water intake and developed a system to measure individual water intake on pasture-based systems, which they plan to begin using next year.

“It is important to measure the individual water intake to be able to do recommendations and cater for all animals on the farm, and we do see a big variation in water intake. With the new system we will be able to study how much drinking water is needed depending on, for example, weather, feed type and milk production levels.”

Schütz is also interested in the effects of heat stress on somatic cell counts and lameness.

“When it’s warm and cows don’t spend much time lying down, is there an effect on somatic cell count and lameness during that period? So that’s something to look into in the future.”

Sprinkler systems are effective at reducing heat stress because water on the cow’s coat helps evaporative cooling. However, it can also increase humidity around cows when they are close together. The effectiveness of sprinkling depends on the removal of water vapour by air movement, and droplet size, which should ideally penetrate the coat, Schütz says.

“It would be ideal to have fans in every yard at the milking shed but that’s just not practicable.”

When it comes to feeding, feed with high fibre content can increase the heat load on a cow because of the heat from fermentation in the rumen. Schütz says if possible it’s best avoid these feeds or feed later in the day so cows are ruminating at night when it’s cooler.

“It’s really just about being prepared and often thinking about how you would feel doing what they do in the heat. It wouldn’t be nice going for a 2km walk at 2pm and it’s the same for cows, so pushing afternoon milking a bit later or looking at once-a-day or 16-hour milking as options should be considered and it also may play a part in early drying off decisions.”

Over the past 10 years research has been done into how to best provide shade, how much shade cows need and blockage from solar radiation, as well as whether cows prefer sprinklers or shade.

“We do know that cooling with water is more efficient than shade as it reduces body temperature and respiration rate faster, but cows prefer shade over sprinklers as they don’t seem to like the water on their heads.”

For solar radiation, the more blockage the better but a minimum of four-five square meters of shade was needed.

“We also found that if cows have access to shade during the day they will typically graze at night when it’s cooler so they can stay cooler during the day and still consume what they need.”

Schütz says she would like to see shade in every paddock, but it’s not always possible.

“Everyone can do something to reduce the effects of the sun. At the end of the day it’s not rocket science, it’s more about getting people aware of the issue and doing something about it. There is a production benefit to keeping cows cool. Along with production benefits, farmers also have an obligation under the Animal Welfare Act to ensure cows have access to sufficient water and shelter as one of their five freedoms.”

Key points

• Danger zone: Air temperature greater than 21C and relative humidity greater than 75%
• A cow’s critical temperature is 39.4C
• Cows can drink more than 100 litres a day so ensuring a good clean water supply is crucial
• Provide plenty of shade
• Use sprinkler systems for cooling in the yards
• Keep an eye on high-producing cows, older cows and Friesian-cross cows that are more susceptible
• Reduce walking distances if possible and walk cows slowly.

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