The sub-zero blasts Old Man Winter threw at us are but a memory.
We smile as we turn our faces to the warm spring sun.
Over the next few months, however, that same sun could cause major
disruptions in your dairy herd. As a result of heat stress, you
Two sources of heat stress can have an impact: environmental temperatures
and the heat produced internally from cows digesting feed, known
as basal nutrient metabolism. The latter source is a lesser factor
than high environmental temperatures.
However, as cows increase milk production and feed intake, they
produce more heat from nutrient metabolism. This aggravates any
heat stress caused by environmental sources. As a result, higher
producing cows will experience heat stress before lower producing
or dry cows, according to published research by J.G. Linn, University
Dairy cattle have a normal body core temperature of 101.3 to 102.8
degrees F (38.5 to 39.3 degrees C). The thermoneutral, or comfort,
zone for cows is an environmental temperature range of 41 to 77
degrees F (5 to 25 degrees C). Within this zone, the heat produced
by their normal bodily functions approximately equals the heat lost
by their bodies.
Environmental heat comes from solar radiation and hot weather.
High humidity and lack of air movement in barns or holding areas
aggravate the problem. Three temperature-humidity ranges play a
significant part in heat stress:
Its been said that "there is milk in fresh air."
Cattle cant dissipate body heat as we do. They can perspire
at only 10 per cent of the human rate. Consequently, you have
to use mechanical means to help your animals maintain their core
body temperatures within the thermoneutral or comfort zone.
One of the most efficient and least expensive ways to provide
a comfort zone, and maximize milk production, is to ensure optimal
ventilation in the holding area. This may require opening the
sides of the barn by removing metal sheeting and installing screening.
If your barn has concrete walls, install fans to ensure adequate
air movement in all sections of the barn. If netting is installed
in the outside walls, you can raise it to increase air flow. Increasing
the roof venting will also enhance air flow.
Beat the Heat Outdoors
Outdoors, cattle should have the benefit of shade in feeding
and resting areas. If these areas lack trees on your farm, you
can erect netting over them.
When installed over a clean surface impervious to water, such
as concrete, misters can also help to reduce heat stress. Install
misters so that they wet only the front one-third of the concrete
pad. This prevents development of wet or muddy areas which could
lead to mastitis problems.
Set misters to deliver no more than a fog. If you see water dripping
from your cows udders, adjust them to deliver less moisture.
Also, avoid installations that can make feed wet and develop mould.
Adjust feeding too.
Heat stress reduces feed intake eight to 12 per cent, and sometimes
more, causing reduced volatile fatty acid production in the rumen
and decreased milk production. To address this problem, pack more
nutrients into smaller volumes of feed. Requirements for lactation
dont change, but the amount of energy your cows need to
remain cool increases.
During the hot months, your cows deplete minerals more readily
through excessive water loss. Properly using buffers in the diet
can help compensate.
Be sure to confer with your feed consultant before making any
drastic changes to ration formulation.
Altering feeding patterns can also help to ensure your cows consume
adequate feed. Multiple feedingthree times per day, for
exampleensures feed will be fresher, thus increasing dry
matter intake. This also lets you or your herdsperson observe
the cattle more closely. During hot weather, cattle prefer to
eat at night and after milkings. Feeding 60 to 70 per cent of
the ration between 6 p.m. and 8 a.m. increases milk production
successfully during hot weather, according to Linns research.
Water, Water Everywhere
Your cows water requirements increase dramatically as environmental
temperatures increase. Provide additional sources of water for
them. At environmental temperatures above their body temperature,
however, their water intake decreases because of reduced dry matter
intake and inactivity, note the University of Missouris
J.F. Keown and R. Grant.
You should increase the recommended ratio of one waterer for
every cow during hot, humid weather. Cattle should have access
to an unlimited quantity of fresh, clean water in an accessible
Cooling the water to the preferred temperature of 70 to 80 degrees
F (21 to 27 de-grees C) has also proven effective in increasing
intake. Research published by R.G. Dado and M.S. Allen in the
Journal of Dairy Science concludes that the value of added milk
production should offset the cost of cooling the water.
Hot Weather Checklist
Reduced dry matter intake is the main reason for decreased production
during times of heat stress. As intake decreases, the cow uses
more energy in an attempt to maintain a comfortable body temperature.
That reduces the availability of nutrients and energy for milk
production. So, when hot, humid weather sets in, be prepared to: