Summer Coliform Mastitis,

Dr. Normand St-Pierre, Dairy Management Specialist, Ohio State University (top of page)

As I write this column, outside temperatures are well above 80oF in Ohio and we are just in early May. Is this unusual? Well, considering that the average of our daily maximum temperature is approximately 70oF in central Ohio during the first half of May, these daily highs are certainly above average. But, it is not unusual to experience a "heat wave" where temperatures exceed 80oF in early May. Actually, it would be very unusual not to have at least three days where temperatures exceeded 80oF in the first two weeks of May. If we look at weather data for Central Ohio, in 67 out of the last 70 years, we have experienced three or more days of daily maxima exceeding 80oF in the first two weeks of May. Factoring the relative humidity, which averages 55% in mid-afternoon, we quickly realize that our cows do experience episodes of heat stress in Ohio during the month of May. On an average year, there are eight days during the month of May where the temperature-humidity index (THI) exceeds 70, putting our cows under heat stress. And heat stress is expensive, costing $19.0 to 33.5 million per year to Ohio's dairy producers. You can greatly reduce these losses by:

1) Starting now. If you have fans, clean them up. The crud that accumulates on the blades and screens can easily reduce their efficiency by 50%. If you have sprinklers, verify each nozzle, clean the water line, and don't wait until it gets really hot to see if the sprinkler system works. If you have movable sidewalls, windows, etc., it is time to open them up. From now on, your cows are considerably more likely of getting too hot than of getting too cold.

2) Starting at the right place. Have a close look at your operation and identify where your cows are most challenged by thermal stress. On some farms, this is in the yard where cows have to stand by an uncovered feed bunk to slowly get cooked by solar radiation. A simple and inexpensive shade cloth can really make a difference in these instances. In general, however, our holding pens are the biggest culprit when it comes to heat stress. In older parlors with lower ceilings and low sidewalls, it is very difficult to move out of the facilities the heat produced by a bunch of milking cows stacked tightly with less than 15 ft2 per cow. It takes fans (and a lot of them) to control heat stress in a holding pen: somewhere around one 36" fan per 120 to 150 ft2 (or roughly one fan per 10 cow capacity in the holding area). Adequate use of sprinklers (one minute on per five-minute cycles) can be very effective at reducing heat stress as long as adequate outside air can be drawn into the holding area. Otherwise, the water evaporating from the cows' backs saturates the air, resulting in one big sauna and a gigantic heat-stress mess.

Alleviating heat stress does not have to be overly expensive. Returns on investments generally exceed 3:1 (a $30/cow per year in equipment depreciation, interest, and maintenance plus the operating costs results in an additional $100 in gross returns).

Just don't wait!