Livestock
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Treating cows with heat stress
SUMMERS might be getting hotter but for modern dairy cows heat stress has become a year round problem, says MDC extension officer in the South West, Piers Badnell.
He explains that heat stress can lead to an immediate drop in dry matter intake and milk yield, and the effects on fertility, production and lameness can last for months.
"Heat stress might be something we worry about only in the summer but higher yielding herds in particular, and units where cows are housed full-time to optimise management, are seeing signs of heat stress all year round," says Piers.
"Heat stress is the discomfort caused by a combination of temperature and relative humidity - known as the Temperature Humidity Index (THI). A moderate temperature, but high humidity such as on a foggy November day, can cause heat stress. Poor ventilation and the trend towards increasing numbers of roof lights have created warmer buildings with high humidity - even in winter.
"It only needs to be 24C at 100% humidity for a cow to go into heat stress - and if it's 14C outside, a shed with poor airflow soon adds another 10C to the inside temperature. In hot, dry summers temperatures can reach 30C with 20% humidity before affecting cows. Different combinations can be checked against a chart on the MDC's Housing the 21st Century Cow CD Rom or on the table below," he says.
When cows become heat stressed, they can no longer regulate their body temperature and so one of the most obvious signs is panting. Affected cows spend a lot of time at troughs splashing their tongues in the water to try and cool down. Their coats also become wet and sweaty.
"Work at the University of Wisconsin has shown heat-stressed cows also stand for up to 50% longer," explains Piers. "This has a knock-on effect on lameness as they can develop sole ulcers and longer contact with slurry increases the risk of digital dermatitis.
"Increasing airflow by adding fans, removing sides from buildings or reducing stocking density can make a real difference to cows. Think about replacing boarding and breeze blocks with climate controlled blinds, which use heat and humidity sensors to open up automatically.
"When cows are at pasture fields with trees are not the answer," stresses Piers. "Last summer anecdotal evidence showed more cases of mastitis in cows which congregated under trees to keep cool as the high stocking rates led to contaminated, poached areas. Instead bring them into shady buildings or loafing areas and if necessary think about housing cows on really hot sticky days and letting them out to graze at night when it's cooler."
To contact Piers Badnell telephone 01989 740562. The MDC's "Housing the 21st Century Cow" pack includes a booklet and CD Rom offering a one-stop shop for producers considering investing in new dairy cow housing, or adapting their current set-up to suit changing needs. For a copy of the booklet telephone 01285 646510.
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