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The heat is on - consider your cows

By Martha Camps, Te Awamutu


2018 NZ’s hottest year on record – climate scientist.” NZ Herald.

“One summer left: On Haumoana’s beachfront, the climate change hourglass trickles.” NZ Herald.

Since we’re all experiencing the warmth at the moment I decided to connect the dots between dealing with high and possibly rising temperatures and dairy farming.

Having spent some time on dairy farms in Israel and Vietnam I always have a visual reminder of what good (and bad!) heat management for dairy cows looks like. In the last NZ Dairy Cattle Veterinarians Conference I saw a few interesting presentations linking the overseas work to New Zealand conditions.

A survey of 291 farmers in 2017 indicated that 3-quarters were concerned about heat or cold stress on their farms. When asked why they were concerned about heat stress, 87% mentioned welfare or cow comfort, and only 30% mentioned impacts on productivity.

The most frequently used measure of heat load and risk of heat stress is the temperature humidity index (THI), this incorporates the effects of ambient temperature and relative humidity. A THI threshold of 72 has been used to define heat stress, based on a reduction in milk production. Recent evidence suggests that the THI threshold for decreased milk production is lower than 72 for pasture-based cows in New Zealand. For example, a reduction in milk solids started to occur at a 3-day average THI of 68 in Holstein-Friesian cattle. This could be because the THI does not account for solar radiation, wind, increased activity walking to and from milking and their pasture diet, relative to housed cows. Using the THI as an indicator may not be optimal here although it’s the best tool currently available. The Waikato on average has 62 days where the THI exceeds 70.

Shading is an essential component of heat management and results in higher milk yield, and decreased body temperature and breathing rates compared with unshaded animals. Insufficient access to shade or drinking water results in increased aggression between cows due to competition, and may also cause frustration. More shade equals less aggression and more milk.

Water sprinklers used at afternoon milking are very effective at cooling cows quickly. Dairy cattle under sprinklers had increased milk production, improved reproduction and improved feed conversation efficiency, compared to cows with no access to sprinklers or shade. Although uncommon in NZ milking sheds, fans can increase the effectiveness of sprinklers. For example, cooling Holsteins with both fans and sprinklers in a pasture-based grazing system (Argentina) for 20 to 30 minutes after walking to the milking shed reduced body temperature, respiration rate, and improved milk yield.

DairyNZ currently is developing a method for determining a farm system’s impact on a cow’s quality of life. Alongside nutrition, health and behavior, the environment will be part of the assessment which will include the thermal comfort of dairy cows. Watch this space!