The Sun’s rays are getting stronger and temperatures and humidity’s in Virginia are starting to rise, so now is the best time to start managing your forages to help make cows – cool cows! For most of us the value of feeding high-quality forages may reach its peak during late spring, summer and fall. Digesting forage generally generates more heat than digesting grain and one way to correct this problem is to feed high-quality forage during the summer. This allows for less forage intake while still maintaining nutritional requirements and a balanced diet. This is because feeding forage that is lower in neutral detergent fiber (NDF) and higher in NDF digestibility allows the cow to process feed in less time and expend less energy doing so. The net effect is a cooler cow during the heat of summer.
Cows take on heat from the environment and generate
metabolic heat from eating and digesting feed. Problems start to occur if temperature
and humidity increase and cows don't have opportunities to balance their
metabolic and environmental heat gains in combination. Like most mammals, a cow needs to maintain its
core body temperature. The core temperature changes slightly throughout the
day, reaching a peak in the early evening and a low early morning.
Metabolic heat (the heat the cows produces within her body) is
being produced all the time. During the day this heat is not as easily
dispersed. If night time conditions are sufficient to allow adequate dispersal
of heat the cow will not suffer ill effects. If this cycle of heat accumulation
during the day and loss during the night is disrupted by high night time
temperatures the effects become more noticeable.
Factors that determine the level of environmental heat a cow
is exposed to over time are:
- air temperature and relative
humidity
- amount of solar radiation
- degree of night cooling that
occurs
- ventilation and air flow
- length of the hot conditions.
How do cows keep themselves cool?
In hot environmental conditions, cows shed heat with a range
of behavioral and physiological strategies.
Examples are:
- looking for areas with greater
air movement or standing to increase air flow around their body
- seeking water and shade
- changing their orientation to
the sun
- panting or sweating
- stopping or reducing feed intake
which decreases rumen heat production.
The effects of Heat Stress can be costly.
Heat loads can build when farm infrastructure doesn't
provide cooler conditions for the whole herd. Decreased milk and calf weight
gains are the clearest cost, but some effects are less obvious and result in
significant productivity losses. These include:
- reduction
in fertility and calving rates
- low
milk components
- body
condition loss
- susceptibility
to infection
Highly digestible forage NDF will help to reduce the overall
heat load on the cow and provide the proper amounts and ratios of volatile
fatty acids to maintain milk production and calf gains. So now is a time to evaluate y0ur forages and
grazing strategies to plan to utilize the available forages to the fullest.
Although providing high-quality forage during the heat of
summer offers an added benefit, please remember conventional means of heat
abatement such as natural shade, barns designed to shed heat, fans, and shade
cloths or portable shades must also be used to realize the full benefits of
feeding highly digestible forages during periods of heat stress.
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