Week 7

Dairy: Lactating Cows

Energy/Carbohydrates

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Energy Terms

• Total Digestible Nutrients (TDN)
  • Expressed as % or lb
• Net Energy for Lactation (NEL)
  • Expressed as Mcal/lb or Mcal

Partitioning of Ration (60% Alfalfa & 40% Corn) Energy and Losses in a Lactating Cow

Energy Partitioning

• During Early Lactation
1. Maintenance
2. Milk Yield
3. Growth
4. Weight Gain
5. Reproduction
• During Late Lactation
1. Maintenance
2. Reproduction
3. Milk Yield
4. Growth
5. Weight Gain

Energy Requirements

• Maintenance
  • 10 Mcal/d (13 lb ration DM)
  • 10 – 15% for pastured and cold stress
• Growth
  • 20% (1st lact) to 10% (2nd lact) above maintenance (1.3 lb ration DM)
• Milk Yield
  • 0.31 Mcal per lb of milk (0.4 lb ration DM)
• Reproduction
  • 3 Mcal/d last two months of pregnancy (4 lb ration DM)
• Weight Gain
  • 2.33 Mcal per lb gain (3 lb ration DM)

Cow Producing 65 lb Milk, Pregnant, Growing, Gaining Weight

CHO Fractions

• Fiber Carbohydrates
  • Cellulose
  • Hemicellulose
  • Lignin
• Non-fiber Carbohydrates
  • Starch
  • Sugars
  • Pectin
  • Organic Acids

Acid Detergent Fiber (ADF)

• Lignin and cellulose
• Cell wall of the plant
• Digestibility is low
• Predicts energy level
• Increases as plant matures

Relationship of NEL and ADF in Corn Silage

Neutral Detergent Fiber (NDF)

• Total cell wall
• ADF + hemicellulose
• Modest digestibility
• Predicts feed intake
• Increases as plant matures

Effect of Ration NDF on Intake

Acidosis

• Low rumen pH (<6.0)
• Cause
  • Type of diet (low fiber or high concentrate)
  • Physical form of feeds (small particle size)
• Effect
  • Shift rumen microbe population & VFA pattern
  • Slow the rate of feed passage
  • Lower feed digestibility

Composition of Selected Feeds

Effective NDF (eNDF)

• Long particles stimulate rumination
• Rumination leads to saliva production
  • Buffers rumen
• Small particle size forage similar to grain
  • Rapid fermentation in rumen
• Goal: 70 – 75% of NDF from forage

NDF and eNDF

Non-fiber Carbohydrates (NFC)

• Sugars
• Starch
• Pectin - citrus and beet pulp
• Organic acids - fermented feeds
• NFC = 100 - %NDF - %CP - %Fat - %Ash
  • NFC and NDF vary inversely
• Optimal range - 35 to 45% DM