—Lancaster Farming, Saturday, September 16, 1972
18
Cool Heifers Keep Regular Cycle
Transferring heifers from cold
to hot climates just before the
breeding season could delay the
time to conception, and feeding
barren heifers cost the producer
extra dollars
Cessation of the estrous cycle
and other marked physiological
changes in cattle may result from
the sudden exposure to high
temperatures However, cattle
can adapt to the higher tem
peratures given time and the
proper diet
The effects of heat stress were
studied by ARS cattle scientists
James Bond and Robert E.
McDowell, Beltsville, Md. Both
summer-and winter-conditioned
heifers were used in four winter
and two sxummer trials
Cattle maintained outdoors
during the summer or winter
were subjected to 90 degrees F.
temperatures in climatically
controlled chambers. Control
cattle were kept inconventional
barns
The heifers received a pelleted
high-energy, low-fiber diet and
water in trials lasting from 56 to
200 days They were allowed to
consume as much as they wan
ted Weekly measurements were
made of hair coat depth and
weight, and daily checks were
made for estrus
Only one summer-conditioned
female out of six ceased normal
estrous cycling, but 18 winter
conditioned females ceased
cycling for periods of 56 to 112
days Estrous cycle appeared
related to the degree of stress
the difference between winter
and high summer temperatures
To further test this relation-
FARM a
ship, six summer-conditioned
heifers were placed in the
chambers during August the
following year and were sub
jected to temperatures of 100
degrees F. Initially,their body
temperatures rose, then declined
slightly, and leveled off. During
the C-week period, all but one of
six heifers ceased to cycle.
Though winter-conditioned
heifers ceased cycling for various
periods of time, they conceived
and bore normal calves once
regular cycling began.
Other changes in heat-stressed
heifers included an average
increase of 52 respirations per
minute, an average temperature
increase of 1.8 degrees F , and a
13-quart increase in water intake
over conventionally housed
heifers.
The most dramatic physical
response to heat stress was
shedding and decreased hair coat
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depth in winter-conditioned
females. In summer-conditioned
females there was no distinct
hair loss. Hair coat depth seemed
to be most closely associated with
adaption of the heifers to con
stant heat stress.
The scientists found that
feeding the high-energy, low
fiber diets and giving the heifers
plenty of water helped them
adapt to the higher tem
peratures. The high-energy, low -
fiber feeding regime should be
kept in mind by producers
moving cattle from low to high
temperatures, because high-fiber
diets produce more body heat
during digestion.
Dr. Bond says that prior
climatic conditioning is im
portant in the heifer’s response to
heat. If possible, it is best to buy
cattle in one’s own climate
region. This is especially im
portant during the breeding
season.
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ganization.
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