Heat Stress in Cattle
Holly McGill, MSc., WFS Ruminant Nutritionist
[Wallenstein, ON]: After a difficult spring that saw many fields of winter wheat turn up dead and prolonged and heavy rains that delayed corn planting and hay harvest, the winds of change may finally be blowing. Fields are planted, the first green rows of corn are popping up, and bunks are filling with first cut. It seems to finally be spring in Ontario – just in time for the month of July. It may seem hard to believe, but the sticky, muggy days of summer will soon be upon us, bringing with them the challenges of managing heat stress in our animals. While it is well known that hotter-than-normal days can temporarily put animals off feed, prolonged heat stress can lead to reduced feed intake, decreased gains or butterfat produced, infertility in breeding stock, and in extreme cases, mortality.
Cattle of all kinds are especially prone to heat stress, as they produce a significant amount of heat from digestion alone, as well as from typical day-to-day bodily functions. Usually they are able to dissipate this heat into the surrounding environment in a number of ways, unless it is too hot or too humid to do so. This is very important to note – heat stress in cattle can set in well before it feels too hot to humans. According to the Temperature Humidity Index for Livestock, cattle can be at risk for heat stress at temperatures as low as 22°C, depending on relative humidity and air flow. Even though it may not feel like you need to, it is important to monitor your herd for signs of distress such as laboured breathing or panting, bunching in groups to decrease sun exposure, and increased saliva production. Milk producers would do well to monitor their pick up results frequently to watch for decreases in their herd’s fat test.
So what can you do to help prevent heat stress in your herd? As temperatures rise, so does an animal’s water requirements. Keeping water fresh and clean and providing enough trough space to allow for more time spent drinking is critical. Altering the feeding program is another way to mitigate heat stress: feed to intake, not ad libitum; feed the bulk of the diet in the late afternoon or early evening; and consider adding potassium to the diet to maintain electrolyte balance. For dairy farmers, the addition of 200g of bicarb into their cows’ rations is a relatively inexpensive way to help preserve their butterfat yield, as well as focusing more on digestible and fermentable fibres in the diet rather than starchy, high-energy ingredients. You should also avoid handling or processing cattle during the hottest times of the day, and consider implementing different airflow or wetting-down tactics in confined herds.
Though heat stress is a known risk to animal welfare and performance, being aware of the increased risk to cattle and having a plan in place to help prevent it can ensure both you and your herd enjoy the long days of summer ahead!