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Nutrition adjustments for heat stressed dairy cows

Noah B. Litherland, Dairy Nutritionist and Zach Sawall, M.S. Research Assistant University of Minnesota

July 14, 2012

Heat stress is detrimental to dairy production and affects feed intake, rumination, nutrient digestibility and absorption, which in turn can decrease milk and component yield. According to University of Arizona researchers, decreased feed intake only accounts for about 35% of the decrease in milk yield during heat stress. Heat stress can also reduce the responsiveness of the liver to key hormones (growth hormone and insulin like growth factor-1) that are important determinants of milk yield (Rhoads et al., 2010). It appears that heat stress may reduce the capacity of the cow's liver to make glucose which makes lactose. Lactose is the key factor determining milk volume.

Three key areas to consider when developing a nutrition plan to cope with heat stress:

Intensively manage high risk groups during heat stress:

Feeding management adjustments:

  1. Water is the most important nutrient. Consider adding another water tank to the pen and keep drinking water clean and in abundant supply.
  2. Alter feeding times to deliver feed during the coolest part of the day.
  3. Increase the number of daily feeding times (mix smaller loads) to keep feed in the bunk cool.
  4. Make sure high moisture feed ingredients (distillers and corn gluten) are fed before they experience secondary fermentation (heating).
  5. Consider using a bunk stabilizer such as propionic acid. These commercially available products reduce growth of yeast and molds in silage when added during the ensiling process.
  6. Minimize TMR sorting by increasing feed push up and evaluating particle size.
  7. Manage bunker faces to minimize exposure to oxygen. Remove only the amount of feed from the bunker needed to feed cows in the next hour and ensure that removal rates are adequate to prevent secondary fermentation of the silage.
  8. Avoid mister spray onto feed. Excessive wetting of the TMR can reduce palatability and accelerate bacterial growth in the bunk reducing feed quality. Keep a clean bunk. Remove all feed refusals daily before any new TMR is fed. Avoid TMR dry matter content less than 50%.
  9. Plan on lower dry matter intake during heat stress and work with your nutritionist to adjust diets accordingly. An example is to increase the nutrient density of the diet to reflect actual dry matter intake, which is typically reduced during heat stress.

Feed ingredient adjustments:

  1. Increase the energy density of the diet and reduce the heat of fermentation by substituting carbohydrates with rumen inert fat. Supplemental saturated fatty acids at 1.5 or 3.0% of diet dry matter increased milk yield, milk fat content and yield, and reduced peak rectal temperatures in heat stressed cows (Wan et al., 2010).
  2. Increase delivery of key minerals: phosphorous, potassium and sodium. Supplementation to increase dietary potassium from 1.0% to 1.5% in heat stressed cows in Arizona increased milk production (Schneider et al., 1984). Research also indicated that increasing the dietary cation-anion difference (DCAD) for lactating cows increased milk yield when sodium (sodium bicarbonate) and potassium (potassium carbonate) were added to the diet. Avoid excessive concentrations of dietary sulfate and chloride in lactating cow diets especially during heat stress.
  3. Supplement TMR with yeast culture. Feeding yeast culture improved daily milk yield by 2.6 pounds per cow during heat stressed conditions in California (Bruno et al., 2009).
  4. Future concept: Supplement TMR with rumen protected niacin. Feeding ruminally protected niacin increased evaporative cooling loss and slightly reduced rectal temperatures in heat stressed dairy cows (Zimbelman et al., 2010).
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