Tom: Jill Larson is a Nutritionist with CRYSTALYX Brand Supplements. I’m Tom Martin and Jill joins me to talk about thermoregulation in beef cattle. Thanks for joining us Jill.
Jill: Thank you.
Tom: Let’s begin by asking you to recall a visit to Texas and encountering high heat there and wondering how cattle handle such high temperatures while at the same time you were hearing from Texas ranchers who were curious to hear about how cattle survive the cold northern winters. Can you tell us a little about that?
Jill: I recently traveled to Texas, and I’m originally from Minnesota, so when I got off that plane in July I was greeted by the warm temperatures. To me it felt like walking into an oven it was just that warm. As I was traveling across the southern part of Texas in the heat of the summer, it got me really thinking about how different cows can regulate body temperature in the heat of Texas versus the cold winters in Minnesota. That brought me to this concept of thermoregulation and how cattle can regulate their body temperature.
RELATED ARTICLE: The dog days of summer
Tom: So, for the most part cattle producers know that cattle can regulate their body temperatures, but why is it important for them to understand how they do that?
Jill: Regulating the body temperature is important for cattlemen to really understand as it ultimately plays a big role in the herd’s profitability through proper selection and supplying their cattle with the right nutrients – especially energy. The regulation of body temperature within an acceptable range to help avoid either heat stress or cold stress is termed “thermoregulation”. The body temperature can be affected by things like hair coat thickness, body condition, wind, humidity, shelter from the elements, the diet and acclimation to the weather – among others. So, one of the first things that may come to cattlemen’s minds as we talk about regulating body temperature in cattle are the different breed differences. The eared cattle or Bos indicus breeds typically found in the south versus breeds in the north – the Bos taurus breeds. The breed selection across the country has demonstrated that the importance of breed traits, for example the transfer of metabolic heat to the skin is lower in those Bos indicus cattle but the ability to release heat from the skin through evaporation is greater than in Bos taurus. Also, differences in hair coat color and thickness between breeds is important when selecting those breed differences to regulate body temperature. When body temperature is regulating within a comfortable range based on those different traits then the temperature falls within what we call a “thermoneutral zone” where no additional energy is needed to either produce heat or give off heat from the animal’s body. The thermoneutral zone occurs when the basal metabolic rate is met – which is the amount of energy that is needed at rest in neutral temperatures. These temperatures in the thermoneutral zone typically range between 41 degrees and 75 degrees Fahrenheit.
Tom: So, between really hot summer days and really cold winters, temperatures can fluctuate in and out of that thermoneutral zone. Are cattle able to adapt to these temperature extremes?
Jill: Yes, certainly and that’s really why we see cattle thrive in these different environments. When temperatures are above the thermoneutral zone – one average above about 75 degrees Fahrenheit – this falls under the upper critical temperature category and as a result increases the basal metabolic rate. This then stimulates heat loss to maintain body temperature or else it could lead to heat stress. So, energy is required that then increases as a result of working towards releasing that additional heat.
Tom: And what happens when cattle are under heat stress conditions?
Jill: Under hot temperatures – moving towards heat stress conditions – we typically see a decrease in feed intake. Dry matter intake may reduce as much as 25 percent while temperatures fall in this upper critical temperature category and have an increase in energy requirements to maintain body temperature. This could lead to a decrease in feed efficiency and cattle may experience a negative energy balance.
Tom: Jill, anything that we haven’t touched on here that you would like to add?
Jill: Yes, just to add on to that just a little bit – a negative energy balance due to heat stress conditions could cause a decrease in productivity in a number of scenarios. For example, fall calving herds are often in late gestation in the heat of the summer – and similar to this – during breeding season of the spring calving herds temperatures are on the rise and the decrease in intake and increase in energy resulting in a negative energy balance could have negative impacts on reproductive performance measures and also late gestation nutrition.
Tom: CRYSTALYX Nutritionist, Jill Larson. Thanks, Jill.
Jill: Thank you.