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Heat stress in calves

How Hot Is Too Hot?

Most of us welcome the sun and long hot summer days, however, for farmers high summer temperatures bring the risk of negative effects on livestock and they need to change how stock is managed.

There’s no ducking the issue, the world’s average temperature is rising,” says Dr. Amanda Dunn from Bonanza Calf Nutrition. “Studies have been carried out to understand the impact on farmed cattle, but with temperatures continuing to climb, this is not something to be complacent about – the performance, health and wellbeing, and ultimately financial impact can be significant.”

Heat stress occurs in calves when they absorb more heat than they can expel, leading to discomfort, reduced feed intake, poorer productivity, and impaired fertility.  Calves, especially those in hutches or south-facing sheds, may suffer from heat stress, meaning reduced appetites, especially for dry feed, and experience greater respiration rates and rectal temperatures and as a result, poorer growth rates.

NASA’s scientific evaluation study – average surface air temperatures 2011-21

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Humidity, something that can climb quite high in the UK, coupled with high temperatures really is your enemy,” adds Dr Dunn. “Combined, they are referred to as the Thermal Humidity index (THI)”

Why is this important?  One important reason is that calves alter their lying behaviour and drink more water as they are impacted by a high THI and they can become dehydrated,” Dr. Dunn explains. “If they are then exposed to scour or pneumonia-causing bugs, they may succumb very quickly because their immune system is weakened while their body focuses on trying to control body temperature.”

Calves attempt to maintain a constant body temperature regardless of the outside temperature, and within a certain temperature range – the thermoneutral zone, approximately 0˚C – 23°C in a one-month-old calf. Often, they can accomplish this without expending extra energy. 

But the thermoneutral zone is not constant and it is affected by many things out of a farmer’s control including the effective ambient temperature being experienced by the calf. This is influenced by air movement, moisture, hair coat, sunlight, bedding, and rumination.

June to early September are the main risk periods and US work has found that hutches can be 2’C warmer than the ambient temperature, especially on calm days in exposed sites,” Dr. Dunn goes on to explain.

How Hot Is Too Hot?

Recent work undertaken in Italy and Spain has established the threshold in pre-weaned calves in Europe.

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In the zone above 77, calves will become uncomfortable while in a THI above 80, calves can no longer regulate their body temperature, they will have a raised respiratory rate and will be extremely uncomfortable,” says Dr Dunn. “Work in the USA indicates that calves experience less stress when the temperature drops overnight – they can effectively re-set. Continuously high day and night temperatures as we saw last summer, is when serious problems can start. This is because of the build-up of heat within the calf. As hard feed intake reduces, rumen development slows, something that will affect that animal for some weeks and months in the future and will lead to a growth slump at weaning.”

Strategies To Beat The Heat

  • Provide shade – An 80% shade cloth positioned above hutches can reduce the temperature inside the hutches by 16%1. Meanwhile in sheds, providing shade against direct sunlight can also be helpful.
  • Move the air – Make the most of prevailing winds and ensure vents are open. In sheds, running a fan between 8am – 5pm was shown to improve average daily gains by 23% and feed efficiency by 20% for calves in a comparative shed without a fan2.
  • Offer plenty of water – As calves attempt to maintain their body temperature, water is lost through increased respiration and evaporative cooling (sweating). There is also evidence to show that regular, daily cleaning of water buckets helps ensure intakes remain at a good level.
  • Offer Shine Heiferstart – This summer, Bonanza Calf Nutrition will be including a heat stress additive to Shine Heiferstart to support calves during high temperatures. Especially important if the dam suffered heat stress – meaning the calf may be lower birth weight and colostrum quality poor – the additive has been developed and tested in Italy.

Trials in Italy in conjunction with the University of Milan, over two years, showed the Bonanza Heat Stress additive reduced respiration rates by seven-eight breaths/minute, and rectal temperatures (0.5’C) for any given THI. Weight gain improved by as much as 30% during this period and calf health treatments fell by a third when fed Shine Heiferstart with Bonanza’s Heat Stress additive 

The new additive allows calves to better combat thermal stress, which is better for animal health, welfare, and comfort,” explains Dr Dunn. “By improving respiratory rate and significantly reducing rectal temperature, the calf will be much happier. This leads to better growth, improved feed efficiency and an overall better health status.”

Shine Heiferstart is available via the usual Bonanza stockists

References

1 Coleman et al., 1996

2. Hill et al., 2011

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