Grazing in Michiana
Heat stress can be a big problem for dairy cows, and it requires action. The first step is to recognize some of the signs of heat stress in cows on pasture:
• Packing up in a tight group. Both heat stress and biting flies can cause this. Both often happen together, so I keep the cows sprayed for flies as well as taking action to cool them.
• Panting, with their tongues hanging out like a dog, is one of the most severe signs of heat stress.
• A significant drop in milk production.
The ways I work at this are:
• Having an adequate supply of drinking water available at all times.
• Giving them 75-80% of the daily grazing area at night. Cows stop grazing as the temperature rises during the day, but at night when it is cooler they will fill up and make up for some of what they didn't eat during the day. It takes a little bit of an adjustment period for the cows to get used to this different feeding pattern.
• Using water for evaporative cooling in the feeding and holding areas so they will eat. It is important to have streams of water that soak to the skin, as a fine mist will coat the hair and make them even hotter. With the skin wet, the water begins to evaporate and cools the cow, although this is much more effective when there is a breeze.
If it is a real hot day and they come up hot, it takes about half an hour for them to cool down, begin chewing their cud and feel like eating again. Depending on the time of day, I will either send them back out to pasture or give the afternoon feeding at the bunk and start milking during the heat of the day.
If pasture consumption drops way off, I increase the amount of forage/baleage at the bunk. It is very important that they keep eating something. During the really hot times, I even use the water during the morning milking to cool them before they head out to graze.
My inexpensive cooling system uses a one-inch black plastic waterline fastened horizontally about 6 feet up along one side of the feeding/holding area. I hook one end to a water supply and plug the far end. Then I use a 16-gauge needle to poke holes along the waterline about every two or three feet so that the water shoots out over the cows. I poke the holes in at different angles in order to cover the area where the cows are standing. (There is no roof over them.)
The water line is about 200 feet long and we can cool 170 to 250 head. The number of head depends how wide and long the area is that we are using. The cement has a slope to it so the water runs off easily. One of the lines has 70 psi and the other one has about 50 psi. Both lines are run straight off the wells.
My goal is to keep the cows cool to maintain dry matter intake, milk production and reproduction. Keeping them cool can reduce daily milk loss from 15-20 pounds down to 5-10 pounds per cow in very hot weather. Keeping cows cool helps them get pregnant and maintain those pregnancies during the heat of the summer, which is very important for a seasonal-calving herd. The economic returns from keeping cows cool are very significant.
Another important thing that should happen in August each year is to slow down or lengthen the grazing rotation. From about mid to late April through the middle of August on our well-irrigated pastures we can maintain about a 15-day grazing rotation. On Aug. 15, we need to go to a 30-day rotation because the amount of daylight is getting less so the plant growth slows because there is less light for photosynthesis to happen.
If we want a good supply of high-quality pasture until Christmas we need to lengthen the rest period now. We do this using temporary fence to control how much area they have to graze each day. If you have enough additional acres you can add into the grazing area that is another way to lengthen rotation.
During this time of the year, the grass plant produces leaf growth rather than trying to produce seed heads like they do in the spring. So we need to allow it to grow longer between grazings so it has more leaf to capture sunlight and do photosynthesis. I learned this the hard way. I wouldn't slow down and would run out of pasture by late September to mid October. But since I learned to control the rotation we have grass until Christmas most years.
Mike Martin invites readers to send in grazing-related questions for him to answer in future columns. Readers should send their questions to: mikesue.martin@gmail.com.