During Heat Stress, Can the Efficiency of Nutrient Use Be Altered in Lactating Dairy Cows

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During Heat Stress, Can the Efficiency of
Nutrient Use Be Altered in Lactating Dairy Cows?

• Proposal for Milk Check-Off
• Florida Dairy Farmers - 2007

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Justification

• DMI drops drastically in summer due to heat
  stress while maintenance costs increase by up to
  20 (NRC, 1981)

DMI and milk yield losses, pounds/year
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Justification

• Metabolic heat large part of heat stress
  (Chandler, 1994)
• High HI feeds increase metabolic heat and thus
  heat stress

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Background

• Heat Increment (HI)
• Measure of the heat production due to digestion
  of a ration (Mcal/Kcal NEL)
• Inefficiency of metabolism
• ME - NE
• Contributes to metabolic heat
• Along with heats of digestion fermentation
• Compounding effect

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Background
Lactation 25.5
Product 52.9
Body Heat 31.1
Digestion/Fermentation 20.5
Body Waste 43.4
Maintenance 23.5
600 kg cow, 40 kg of 4 milk Coppock, 1985
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Materials Methods

• 33 lactating cows
• Three diets
• High HI, ad libitum
• Low HI, ad libitum
• Low HI, restricted intake to NEL Mcal/100 kg BW
  of paired cows on diet 1

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Effect of dietary heat increment on respiratory
rate.
Respiratory rate 1 v 2, NS 1 v 3, Plt0.01
Statistical comparisons Hi_AL 1
Lo_AL 2 Lo_Res 3 Contrasts 1 v 2 1
v 3
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Effect of dietary heat increment on body
temperature
Body temperature 1 v 2, NS 1 v 3, Plt0.01
Statistical comparisons Hi_AL 1
Lo_AL 2 Lo_Res 3 Contrasts 1 v 2 1
v 3
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Effect of dietary heat increment on production
DMI 1 v 2, Plt0.03 1 v 3,
Plt0.001 Milk NS ECM NS Statistical
comparisons Hi_AL 1 Lo_AL 2
Lo_Res 3 Contrasts 1 v 2 1 v 3
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Effect of dietary heat increment on production
DMI/BW 1 v 3, Plt0.008 Milk 1 v 2, Plt0.07 1 v
3, Plt0.001 ECM NS Statistical
comparisons Hi_AL 1 Lo_AL 2
Lo_Res 3 Contrasts 1 v 2 1 v 3
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Materials Methods

• 8 lactating dairy cows, ruminally cannulated
• Diets Low heat increment (LoHI)
• High heat increment (HiHI)
• Feeding regimes
• Limit fed restricted to 95 of NE needs
• High fed Force fed through rumen cannula to
  110 of NE needs.

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Materials Methods

• 2 x 2 factorial arrangement of treatments

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Objectives

• To determine the effect of low and high
  theoretical heat increment diets on production
  and apparent efficiency of feed conversion and on
  heat stress in lactating dairy cows.
• To determine if limit feeding or force feeding
  influence efficiency of nutrient use or the
  severity of heat stress.
• To determine if an improvement in milk yield,
  efficiency of production, or economics
  accompanies feeding low or high HI diets.

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Diet make-up.

• Low HI diets relatively high levels of fats, and
  fermentable grains and forages
• High HI diets relatively high levels of fibrous
  by-products, less grain or fat

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Experimental measures.

• DMI, milk yield, milk composition, body weight
• Nutrient digestibility (DM, ADF, NDF, CP) to
  quantify gross energy status
• Apparent energy balance
• Body temperature intra-vaginal probes (5 minute
  intervals)
• Temperature and relative humidity (5 minute
  intervals)
• Blood samples collected twice, serum analyzed
  for glucose and urea N.
• Rumen pH and ammonia

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Potential Study Benefits

• Efficiency of nutrient use in hot weather
• Determine efficiencies associated with dietary
  heat increment
• Economic comparisons to compare cost, yield, and
  efficiency benefits of rations
• Comparison of effects on heat stress with
  marginal energy vs. high energy intakes