Cattle can
withstand low temperatures to -37 degree C but temperatures over 23 degree C
(73 degree F) can cause stress when combined with high humidity, low air movement
or direct sun, can cause rapid dehydration in calves.
Heat stress
can reduce productivity, cause reproductive problems such as reduced semen
quality and lower birth weights, and compromise the immune system. Heat stress
will reduce milk production in dairy cows. The effect is more pronounced in higher
producing cows. Heat stress also lowers natural immunity making animals more
vulnerable to disease in the following days and weeks. Problems with lameness
occurring up to a few months after the event may also be attributed to heat
stress.
Tolerance to
heat varies:
• Holsteins
are less tolerant than Jersey cows.
• Beef
cattle with black hair suffer more from direct solar radiation than those with
lighter hair.
• Lactating
cattle are more susceptible than dry cows because of the additional metabolic
heat generated during lactation.
• Heavier
cattle over 1000lbs are more susceptible than lighter ones.
• Sick or
previously stressed animals are susceptible as are recently fresh cows.
• Cattle,
alpacas and llamas are more prone to heat stress than sheep and goats
HOW TO REDUCE AND AVOID HEAT STRESS
Provide
shade from direct sunlight; e.g. trees, temporary shade using portable shade
cloth blocking 50% of radiation, or permanent structures. All cows should be
able to use the shade at the same time and there should be enough space for
animals to lie down. Research on beef cattle shows improved weight gains and
feed conversion efficiency with 45 sq ft. Provide ample, cool, clean water in
shade near loafing areas. Cows will not travel across 30 metres of open field
when temperatures, humidity and radiant solar heat are extremely high. Provide
at least 1 watering station per 20 cows, Cattle on range should be readily able
to access water. Add extra stock tanks if necessary. In normal conditions the
recommended maximum distance cattle should travel to water:
• Increase
air flow over the animals. Efficient of fans will help alleviate heat stress when
animals are housed. All vents should be fully open.
• Minimize
time spent in holding pens before milking.
• For dairy
cows in pasture-based systems the use of sprinklers while the cows wait for the
afternoon milking reduces heat stress. Sprinklers also reduce irritation from
insects.
• Avoid
handling cattle during hot, humid weather. If it is necessary to carry out stressful
events (e.g. castrating, vaccinating), do it in the early morning.
• Avoid
transporting livestock in hot weather; move between 8pm and 8am and reduce
loading density. Do not move animals from a relatively cool environment to a
hot environment during the summer.
• Reduce
biting fly populations (with improved sanitation, repellents and traps) which
tend to cause cattle to bunch together.
• Provide
access to high quality forage (e.g. first cut dry hay) in feed bunks in shaded
areas even if cows are also on good quality pasture.
• If
finishing cattle, shift daily feed delivery toward evening.
• When
using management intensive grazing, rotate through fields more quickly - taller
grass is a cooler surface; rotate in evening rather than in the morning; graze
paddocks that allow access to barn or trees during the heat of the day.
TREATMENT OF SUNSTROKE IN CATTLE OR HEAT EXHAUSTION
Treatments
to lower body temperature include cold water submersion, cold water enemas, ice
applications, alcohol rubs and in the case of sheep or llamas, cold water
applied to body parts with little wool (head and lower legs). Move to cool
shaded area. Provide oral administration of fluids to dehydrated animals. Homeopathic
remedies can provide relief if sunstroke is indicated with very high
temperature, rapid pulse, shallow breathing and a reluctance to move.
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