Keeping Cool
Go out to your free stall barn on a cold winter morning and your cows are probably lying down. Not so
long from now, on a hot summer morning, they will be standing up. Why? Drs. Nigel Cook and Ken
Nordlund from the University of Wisconsin looked more closely at this behavior. Using temperature
sensors attached to a CIDR device, they measured body temperature over time in the winter and
compared it to positioning during summer. They found a very straightforward pattern: Cows’ body
temperature drops when cows are standing and increases when lying down (about 1 degree F per hour
of lying). Putting this somewhat differently, cows gain heat when lying, and lose heat when standing.
This is important because, during warm weather cows must stand to cool off, and they will gain heat
while lying down. Thus, on warm days both the length of lying bouts and the total time of daily lying
bouts decreases. As the temperature-humidity index goes up, they eventually cannot lie down at all, and
must stand to simply stay alive. When cows spend more time standing, they ruminate less, they are
more prone to develop foot problems, and, in free stall facilities, they may get dirty from splattering
manure. Cook also studied the incidence of foot lesions, and found that non-infectious foot lesions peak
about two months after the most severe heat events. It takes about two months for hoof tissue to grow
from the corium to the sole, so perhaps this is why sore feet peak about two months later.
What about holding areas? Cows are standing, but because they are often packed closely they usually
gain heat instead of losing heat. Another problem with holding areas is that the air that cows breathe is
often incredibly polluted with infectious organisms because of the cow density and lack of access to
fresh air. Thus, holding pens are not a great place to be on a hot day.
Do your cows bunch up in the middle of the barn? Bunching cows are hot cows. Hot cows avoid light,
and the middle of the barn is almost always darker than the rest. Flies sometimes aggravate bunching,
but really, if your cows bunch together, they are hot. Getting them to stop bunching means cooling
them.
Humans feel cooler when air is moving, and in general the faster the air is moving, the cooler we feel.
This is not entirely true for cows however. As the ambient temperature approaches body temperature
cooling occurs due to evaporation of moisture, in our case, evaporation of sweat. Cows do not sweat
like humans, so they cool differently. For cows to be cooled, their skin must be wet, or they must cool
by evaporative panting. Air movement alone is not sufficient to cool cows at these temperatures. Just
because we feel cooled does not mean cows feel the same. Increasing air speed beyond the optimal of
about 2.5 to 5 mph does not increase cow cooling either. Thus, cooling with air movement alone is not
sufficient to cool cows.
Our response to keeping cows cool has been to provide lots of air and water, not necessarily when and
where cows need it, but where we are able to do so. We provide way more air speed and water than
necessary in some areas, and not nearly enough in most. For example, air leaves fans in a cone and
decelerates rapidly as it moves further from the fan. Thus, for most three and four foot diameter fans,
the spot of actual effective airspeed is within 10 to 15 feet of the fan. This is much less than the typically
recommended fan spacing of 10 times the fan diameter. Furthermore, it is difficult to place fans low
enough in most barns to maximize the zone of effective airspeed because fans need to be mounted high
to be safe from cows and skid loaders. High placement results in either a very steep angle, with a short
effective zone, or an effective zone that is above the backs of the cows.
Now that we understand that ideally every cow would have access to moving air and cooling water at
all times, new cow cooling designs are emerging. For holding areas a promising new design uses positive
pressure tubes. These systems have been installed, with success, in many calf and heifer facilities
around the world. For holding areas, greater airflow is needed, so tubes and fans tend to be larger, the
holes in the tubes are larger, and the tubes are placed closer together. With proper design, a positive
pressure ventilation system can almost reach the goal of having 2.5 to 5 mph wind speed available to
every cow in the pen. Coupled with effective sprinkler systems, tube ventilation may be the best cooling
system available for holding pens located in high humidity regions like the upper Midwest. See the
Dairyland Initiative website for details.
Using positive pressure ventilation in free stall barns has not been fully researched, and presents some
significant challenges. However other ideas like motion controlled sprinkling stations, modified fan
designs and of course, cross ventilated or tunnel ventilated barns all can help. Remember though, for
cows to be cooled in tunnel or cross ventilated barns, you still need water on the cows. The exception is
on low humidity, hot days where a mister system can cool the air of the barn. Research is also being
conducted on stall cooling systems that would allow the cow to lose heat while lying. In the future we
will have more effective cooling systems available in free stall barns. Remember, cows that milk more
produce more heat. It is likely that your cows will produce significantly more milk in the future than
they do today. They will need more effective cooling systems. When summer comes, go out and look
at your cows. Are they standing in the early morning when they usually are lying down? Do they bunch
together in the middle of the day? If so, they are hot and you might benefit from a better cow cooling
system.