Summer is upon us and with it comes the concern about heat stress in cattle. Somerset County, admittedly, doesn't have to worry about heat stress except for a couple of weeks out of the year. But the surrounding areas are frequently hit hard by scorching summer temperatures.
There are two distinct types of heat related problems that we worry about in cattle, heat stroke and chronic heat stress. Heat stroke, or acute hyperthermia, happens suddenly and is often fatal to cattle. Black cows in direct sunlight when the sun is highest in the sky are at highest risk. I've seen heat stroke in cattle as early as late May and as late as early September.
Signs to look for include rapid breathing, frothy muzzle, bloat and inability to rise. In my experience, cows that develop heat stroke are usually affected by some other condition. Usually, that other condition is milk fever.
Fresh cows with milk fever (low blood calcium) usually have a low temperature. A fresh cow outside in the heat of the sun with just a touch of milk fever is especially at risk of heat stroke because cows with low blood calcium lose the ability to sweat.
So, as you can imagine, a black cow in direct sunlight that can't sweat will absorb all of that heat with little ability to dissipate it. While that describes the highest risk, black cows aren't the only cows to get heat stroke. Jersey cows are also at risk because of their tendency to develop milk fever.
I've seen temperatures in cows with heat stroke that have exceeded 110 F. Unfortunately, just bringing down the body temperature sometimes isn't enough to save the cow. I've never seen a cow with a temperature over 109.5 F survive more than a couple of days. Temperatures that high will literally cook the internal organs leading to multiple organ system failure.
I treat these cows by dousing them with tepid water. Cold water arguably might worsen the situation by tricking the internal thermostat to prevent cooling. Douse the cow and let evaporative cooling take place. Direct a fan towards the cow to increase the evaporation. Because most of these cows are just fresh, give a bottle of intravenous calcium to correct milk fever.
Here's two points to remember. First, time is critical so waste no time in getting the cow cooled off if she is suffering from heat stroke. And second, keep fresh cows in the shade near a fan for a couple of days in the summer until the risk of milk fever has passed.
Chronic heat stress, on the other hand, doesn't kill cows, but it reduces their productivity. Reduced milk production, low fat test and poor reproductive performance are all well known to be consequences of heat stress. We see most of the problems when late night temperatures don't fall below 70 F.
Keeping cows cool and comfortable can be a challenge when the summer temperatures rise. It's imperative to encourage dry matter intake to reduce the milk drop. Fans with misters over the feed bunk are a good investment, but they are not without problems of their own. Feed TMR twice a day to minimize heating and frequent push-ups will encourage intakes.
Specific management practices to reduce chronic heat stress will be unique to each farm, so talk to your veterinarian or consultant. Reducing the impact of heat stress will improve milk yield, components and reproductive efficiency and all will impact your farm's bottom line.