There is nothing like farming on a crisp summer morning when the sun has just peaked out, the sky is clear, and you can smell the green grass and fresh air as you walk to do chores. But as you walk around enjoying the 70-degree temps, your cows are already starting to experience heat stress.
    Heat stress can negatively impact all the animals on your farm, which is why it is so important to practice heat abatement (the lessening of heat stress). The optimal environmental temperature for a lactating cow is 40 to 60 degrees, but heat stress also considers the humidity. The Temperature Humidity Index threshold for reproduction is 65, whereas the threshold for milk production is 68. This means you can start seeing negative impacts on reproduction before you start to see them in the bulk tank. In addition to causing poor reproduction and lower production in your milking herd, heat stress can cause milk fat depression, a weakened immune system, mastitis and more.
    Heat stress can also impact embryo development. Body temperature greater that 102.2 degrees can affect the developing embryo from day one to day six and leave it without a heat-tolerant protein. This time frame is when the embryo is most vulnerable to heat stress and increased body temperature. According to University of Florida research, cows that experience heat stress during the dry period produce an average of 14 pounds less milk in the first 30 weeks post freshening compared with cooled cows. Researchers also note that cows experiencing heat stress have a decreased ability to kill and fight off infection.
    Heat stress also can cause cows to calve 10 to 14 days before their anticipated due date. This leads to calves with lower birth weights, which can impact their weight at weaning and breeding age. Calves born from these heat-stressed cows weigh on average 17 pounds less. Additionally, because the cow calved in early, her colostrum is not at peak antibody level if you used a dam vaccine. The success of a dam vaccine is dependent on when a cow is going to calve. Calving a whole two weeks early will result in lower colostrum antibody levels.
    Calves can tolerate heat slightly better than cows but become heat stressed at temperatures reaching above 80 degrees. Calves must use their own energy to keep cool, which means they take away energy from their immune system and growth. This decreases a calf’s average daily gain and lengthens the time it takes them to get bred. You can tell if your calves are heat stressed by watching them for signs of increased breathing, panting, decreased feed intake or increased water intake.
    There are negative impacts of heat stress, so how can we help negate these?
    There are four main cooling methods: shade, water, air and time. Concentrating on all four of these is the most effective way to keep animals cool.
    To start, provide shade over travel lanes or any place a roof is not available. Shade intercepts the sun’s radiation, lowering skin temperatures and reducing heat loads.
    Then, make sure there are fans and sprinklers in the holding pen and the maternity pens. These are the most important locations to keep cows cool. Also put fans and sprinklers above the pre-fresh cow pen. Since your pre-fresh dry cows are carrying the future of your herd, you should concentrate on this area to optimize your calving outcomes. Other places you can add fans are over the free stalls, bedded packs and processing areas, and add sprinklers over the feed lanes.
    If you are not able to install both sprinklers and fans, experts recommend sprinklers over the feed lane and fans over the stalls. Water without fans can increase humidity and negate the benefit of having sprinklers in the first place. Sprinklers, ideally, should wet the back of the animal and then stop to allow the water to evaporate and cool the cow prior to another cycle beginning. Even with fans and water soaking, it will take 30 to 45 minutes to start to reduce a cow’s body temperature, so it is important to stay ahead of heat stress as much as possible. To make sure your fans are blowing in the right direction and over the backs of your cows, use a fogger to mist them, allowing you to check for dead space and visualize how the fans are working.
    In calf barns, use fans to your advantage. As mentioned before, fogging is a great way to tell if the air flow in the calf barn is optimal or if calves are in a stagnate location. Because calves tend to nestle into their bedding, it can be a bit trickier to make sure they get sufficient ventilation.
    If calves are in hutches and fans are not an option, it is a good idea to vent the hutches by elevating them with a cinder block under the back and opening the vents on the side. If you can, move the hutches to a shady area to help with cooling. Changing bedding in warmer months is another potential way to keep calves cool and comfortable. While straw is great during the winter, in the summer months switching to sand or sawdust can help keep calves from overheating.
    Both cows and calves should have access to plenty of cool drinking water in times of heat stress, and make sure to keep water buckets clean. Bacteria thrive in wet, warm environments and a water bucket on a summer day is an ideal hangout. Use light-colored water buckets (white or yellow) to help you easily see when a bucket is getting dirty. Try to extend the amount of time water is offered to calves, even adding another round or two and regularly checking to see if buckets need to be dumped and refilled.
    Mealtime matters too. When it is warm during the day, encourage calves to eat at night when they are cooler and have more of an appetite. You can also add a supplemental electrolyte feeding to help calves rehydrate more efficiently.
    After some grueling winter days in the Midwest, it can be exciting when the sun is warmer, but it is important to keep in mind that what we think of as perfect days can already be too warm for our cows and calves.
    Ellen is the First Defense regional sales and marketing manager for Wisconsin and Minnesota. She is’s a problem solver who loves walking calf hutches and diagnosing protocol drift. A great day is a day spent helping dairy and beef farmers keep their baby calves healthy. Cushing can be reached at