“The climate has been changing since the beginning of time. Globally heat stress management is going to get worse. As the climate changes, much will depend on how we genetically select cows,” says Dr. Lance Baumgard, Iowa State University animal scientist during a meeting in central Pennsylvania. “All of the economically important traits are associated with higher heat production, so cows that are more productive are more sensitive to heat stress.”
The bottom line is modern cows experience heat stress sooner than we think, only some of the milk yield loss is related to reduced feed intakes with the rest due to biochemical changes in the heat-stressed cow. (See part two).
These changes set off a cascade of systemic responses that can have lasting impacts. This includes the dry cows, which have been shown to produce less milk in the following lactation, have impaired repro, and produce calves that are less productive when they become adults.
Demonstrating all of this, Baumgard says: “By far, the most practical strategy with the biggest impact and the biggest return on investment is to physically modify the lactating and dry cow’s environment to alleviate the negative consequences of heat stress.”
He urged farmers to also cool their dry cows and pregnant heifers.
“If you are not cooling your dry cows in Pennsylvania, it’s costing you 1000 pounds of milk in that next lactation. That’s 10 hundredweights of milk x $20 per dry cow in that next lactation,” Baumgard asserts.
Where to spend your money? Baumgard listed these priorities:
1) Water availability (plenty of available clean water is always first and foremost).
2) Providing shade (makes a huge difference in solar radiant temperature).
3) Utilizing evaporative cooling.
4) Fans and their placement (angled over backs).
5) Reducing the walking distance to the milking parlor.
6) Reducing time in the holding pen.
7) Improving ventilation.
Providing good shade and a combination of evaporative cooling and fans are the keys.
“The more water the better, if the water is available and waste is not a problem,” he says.
How to measure the effectiveness of what you are doing?
Baumgard encourages producers to monitor body temperatures and do a winter vs. summer ratio calculation on milk yield and repro. It should not be less than 1.
While evaporative cooling can be problematic in high humidity, Baumgard says it still pays.
He also noted that using fans without water can be detrimental in cases where the ambient temperature is above the cow’s body temperature. Dairies in the hotter and drier climates are adopting evaporative cooling because even though the low humidity helps the heat index, temperatures often exceed the body temperature of the cow, making fans without water a problem.
“When the air blowing on you is warmer than the body, the heat transfer is going the wrong way, so there’s no dissipation. The cow accumulates heat faster,” he explains.
For cattle outdoors, he cites the numbers showing just how important it is to provide shade from the sun. This also comes into play when designing a facility in terms of the angle of the sun at the hottest time of the day in certain parts of the barn.
“The cows will tell us, and they never lie,” says Baumgard. “Give them the opportunity to talk to you.”
Cooling is all about heat transfer. Soak the cow, provide the wind from the fan (3 to 4 m/sec), evaporate the water from the cow, and repeat when evaporated.
“The reason evaporative cooling works is because the energy that is needed to turn the water into vapor – that energy is coming from the cow’s thermal energy,” he illustrated, noting this is a repetitive process and the placement of the line of fans, pointing down at an angle, is critical in the feed alley to get that cooling on the cow’s back.
Exit lanes and holding pens are other important locations to shower cows with fans overhead.
In tie-stall barns, there are more challenges. It’s difficult to do evaporative cooling. In situations where evaporative cooling is not an option, the solution is to cool the air, says Baumgard.
One option he mentioned is ‘swamp coolers,’ which operate by soaking a sponge and sucking the air through the wet pad. The energy required to evaporate the water on the pad is coming from the air temperature, so the temperature of the air leaving the pad is reduced. Again, it’s all about heat transfer.
These systems have even greater cooling capacity in a drier environment. The lower the humidity, the colder the air leaving the pad.
This type of cooling – cooling the air — is used in cross-ventilated barns at a different scale, but smaller, portable coolers are also available.
When considering how cattle are housed, fed and managed to reduce the impacts of heat stress, it’s important to understand what’s happening to the cow and when it begins (see part two.)
The bottomline, says Baumgard, is to prioritize barn layouts, cow flows and management systems that reduce walking distance to the parlor and reduce time in the holding pen.
To further reduce the impact of the crowded holding pen, optimize ventilation and cooling for cows while in the holding pen, provide exit lane cooling and avoid ‘lock ups’ in the middle of the day, he adds.
Avoid handling cattle for vaccinations and other tasks in the middle of the day.
During periods of heat stress, clean water availability becomes most critical, so clean the tanks daily, and consider rehydration therapies, especially in transition cows.
Feeding strategies include more frequent feeding at cooler times of the day such as early in the morning and late at night, frequent push-ups, removal of old and ‘hot’ feeds, and use of TMR extenders.
Baumgard advises increasing bicarb at this time and avoiding the temptation to reduce the fiber content of the ration. “It’s critical to work with your nutritionist on this because we are balancing the rumen acidosis risk with the generation of heat.”
By Sherry Bunting
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'Cause Comfort Matters 