Summer is coming – Are you prepared?

Jim Salfer, Extension Educator-Dairy

May 23, 2009

Spring is going quickly so now is the time to be preparing for heat stress in our dairy herds.  It is not too early to be thinking about control strategies to minimize the production losses that occur due to heat stress. Usually due to field work, the start of the heat stress season often catches dairy producers off guard and unprepared to cope with the rapid upswing in temperatures.

The effects of heat stress are many. It is estimated that heat stress costs the dairy industry $897 million dollars annually.  We are all aware of the decline in dry matter intake and the subsequent rapid drop in daily milk production along with the decrease in reproductive performance. But heat stress contributes to several more subtle, insidious effects on dairy cows. Heat stress also affects the immune system. Heat-stressed cattle are able to fight off normal respiratory or mastitis infections. Figure 1 shows a temperature humidity index and indicates when cows begin to exhibit heat stress.   A quick way to evaluate heat stress is to count the number of respirations on 10 cows in the herd.  If respiration rates are greater than 80 breaths per minute on at least 7 cows, you have a significant heat stress problem.  If five of the 10 cows have respiration rates greater than 100, immediate action should be taken. These cows are most likely exhibiting open mouth panting.

As you prepare for the challenges that summer brings, here is a checklist of items to do in the next month to minimize the effects of heat stress on your dairy herd.

• Review all animal housing for shade and water requirements.  Providing adequate shade and plenty of fresh clean water is the cheapest way to help cows survive the summer.  Make sure all classes of livestock have plenty of water and shade.  Consider providing extra water in the holding area while cows are waiting to be milked and in an area immediately upon leaving the parlor.
• Clean and check fans. Dirty blades and guards can reduce performance up to as much as 30%, wasting electricity and decreasing performance.  Regular cleaning of fan blades can maximize effectiveness.
• Check sprinklers, timers and thermostats.  If you have sprinklers in your barn, check for leaks, and clean and check thermostats and timers.
• Change bedding management.  Bacteria grow more rapidly in the heat and humidity of summer.  Consider bedding more frequently and turn over bedding more rapidly to minimize the risk of mastitis.
• Move calf hutches to a shaded area.
• Open curtains on all facilities.
• Review stocking density.  If you are extremely overcrowded, with the low milk prices, it might be advantageous to sell some less productive cows and decrease stress on the remaining cows.

Another area of importance in managing heat stress in the summer is the dairy ration. Visit with your nutritionist about ration changes for summer.  Not only does the cow’s respiration rate and drooling increase in during heat stress, but there is also a decrease in cud chewing.  Because of this, they are more prone to rumen acidosis.  Therefore, it is important to increase buffers and potassium levels of the diet to compensate for these changes.  It is often tempting to increase energy density by decreasing forages and increasing concentrate levels.  However, be careful because this can exacerbate the effects of decreased cud chewing and you will suffer the long term effects of acidosis and overall animal health.

Here is a list of other feeding management strategies to consider this summer:

• Consider feeding twice a day.  During heat stress, cows are more prone to feed sorting.  Feeding more often stimulates curiosity, provides fresh feed, and will provide a more consistent ration.
• Push up feed more often.
• Check water flow rates.
• Increase frequency of bunk cleaning.
• Increase frequency of ingredient and ration analysis to ensure accurate ration formulation.
• Purchase or harvest of high quality ingredients.
• Minimize drastic ration changes, which force cows off-feed.
• Consider feeding during the cooler part of the day.

Don't forget the dry cows and close up cows. Heat abatement strategies are important for them as well.  Heat stressed dry cows have smaller calves, and are more likely to have still births.  Colostrum quality will be lower and cows will have reduced milk production in the subsequent lactation.  These are consequences you want to prevent from occurring on your dairy.

Good preparation now for heat stress will create less stress on you and your cattle.  This will help to minimize the detrimental effects that hot weather will have on profitability during the upcoming summer.