Trees For Stock Shade
The foliage and trunks of trees can block the sun, providing
some measure of comfort for heat stressed stock. Heat stress
has been shown to have an impact on animal production, fertility
and birth weight as well as animal behaviour.
The graph below shows the estimated effect of providing shade
on the milk production of dairy cows in Florida. The results
show that when air temperatures are high (27oC), providing
sufficient shade may increase milk production by around 20%,
offsetting most of the effect of heat stress on production.
In the trial, dairy cows with access to a cement pad covered
with an insulated iron roof also had conception rates of 44%
compared to 25% for cows not shaded.
Reference: Reid, R. and Bird, P.B.
(1990),'Shelter' in Trees for Rural Australia, ed. K.W. Cremer,
Inkata Press Melbourne, pp 319-335.
Research by the Department of Primary industries
in Queensland compared a number of strategies for reducing
heat stress in dairy herds including iron roofs, sprinklers
and shade cloth. The results confirmed the USA research showing
that shade reduced production losses due to heat stress and
was even more effective than sprinklers alone. Shade increased
milk and fat yield, pregnancy rates and weight gain whilst
reducing somatic cell counts (an indication of infection).
In the hottest part of the year, the sun is more severe when
high in the sky. For trees to be effective, stock must therefore
be able to get under the canopy. Large spreading trees with
a dense canopy held high above the ground are ideal. Having
a clear trunk allows air movement below the canopy, further
cooling the stock. Farmers may need to consider the impact
of stock trampling on the root system of trees and rubbing
or chewing on bark. In the afternoon, when the temperatures
can still be high, tall trees will cast a shadow well away
from the root system thereby reducing compaction by stock.
Heat and Cold Stress
of Farm Animals
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