Preventing heat stress for cattle

Just as we humans don’t perform at our best in hot conditions, neither do livestock. Whether dairy cows , sheep , or any other animal, the effects of the often hot New Zealand summer can be devastating, particularly in the warmer north. And the most common effect of hot weather on animals is heat stress

Today we’ll take a closer look at the condition: why it’s dangerous, what causes it, how to identify it, and most importantly, how to prevent it.

What is heat stress?

Heat stress is a condition brought on by hot and humid weather, and is most prevalent in dairy cows. Having evolved and been predominantly bred in more temperate climates, they are unable to dissipate body heat efficiently. They have a limited ability to sweat, regulating their temperature instead through respiration. Generally speaking they accumulate a heat load during the day, and dissipate it at night.

The ambient temperature comfort zone for dairy cows is in the 4C-20C range. Go above that, particularly in humid conditions, and the cow begins to experience discomfort. If the heat and humidity gets high enough, it begins to put the animal’s health at risk. They are unable to dissipate enough heat, and intensifying symptoms lead to intensifying health effects.

Why is maintaining healthy cattle important?

First and foremost, every cattle or dairy farmer knows that you need to take care of your herd if you want them to take care of you. Heat stress can be a wildly uncomfortable and potentially dangerous experience for your animals, so minimising the discomfort and danger should be your primary goal.

But the reasons for maintaining a healthy herd go far beyond compassion. It perhaps goes without saying that a heat stressed cow is an unproductive cow. During particularly hot periods milk production can be reduced byup to 50%, while reproductive efficiency is also severely diminished, with insemination rates dropping as low as 10%-20%. The economic case for minimising heat stress is thus a compelling one.

Causes of heat stress

The likelihood of heat stress affecting your herd can’t be measured through mercury alone. To get a complete sense of the prevailing conditions, other factors such as relative humidity, ambient temperature and evaporation rate need to be taken into account.

The temperature humidity index (THI) combines all the relevant considerations into a simple number, with dairy cow heat stress occurring between 72 and 99.

• A THI reading below 72 does not induce heat stress on dairy cattle.
• A 25C, 50% relative humidity day is rated at 72, just enough to induce mild heat stress.
• A THI of 78 is enough to significantly reduce milk yield
• A 37C, 100% relative humidity day is rated at 99, inducing the most severe heat stress.
• A THI reading of 100 or above will most likely result in death.

In New Zealand, Northland unsurprisingly experiences the most days warm enough to reduce milk production, with Whangarei recording 129 such instances over the 2018/2019 season. Waimate in Canterbury, meanwhile, experienced just 39 such days over the same period.

Common heat stress signs and symptoms for cattle

As soon as conditions rise above a cow’s zone of comfort – a THI of 72 or more – a physiological response is induced, diverting energy from production to survival. At the cellular level, membranes go into lockdown mode, with some ceasing to operate altogether. Energy is instead almost exclusively used to prevent a rise in body temperature.

There are a wealth of symptoms that can indicate an animal is suffering from heat stress. On a hot and humid day, look out for:

• Lethargy.
• Animals seeking shade and/or wind.
• Agitation, restlessness and a refusal to lie down.
• Accelerated and laboured breathing through an open mouth.
• Sweating and excessive drooling.
• Greatly increased drinking, decreased eating.
• Increased urination (caused by electrolyte loss.)
• A drop in milk yield and lower milk quality.
• Emaciation.
• Increasing instances of infection, disease and other health issues.
• Lower fertility, increased embryo mortality and birth defects.
• Reduced weight gain in growing animals.
• Convulsions, collapse and instances of coma.

By SmartShelters | December 10th, 2020 | How To Guide | 0 Comments