Dairy cow feed rations are formulated by determining the animal's total DMI, nutrient requirements, and the amount of feeds available on farm that must be fed to fulfill said requirements.

The total DMI varies depending on the animal. Variables affecting total DMI are: weight of animal, requirements above maintenance, age, days in milk, and days pregnant. Nutrient Requirements are met by optimizing roughages first, then grains and supplements are added in the balance requirements. The amount of available feed must be determined in order to ensure nutrient requirements are met, as not all of the nutrients from DMI are directly available to the cow.

 

Water Intake

Maintenance Requirement (Dry Cow)	Lactating Cow
40 L/day	Water:milk ~ 3:1

 

Dry Matter Intake (DMI)

Type of DMI	Dry Cow	Lactating Cow
Forage DMI	Approx. 2% of BW	- Approx. 2% of BW (1.8 – 2.2) - Approx. 0.9 – 1.0% of BW as NDF (forages only)
Total DMI	Approx. 2% of BW	- Typically 3.5 – 4 % of BW - Approx. 1.2% of BW as NDF (total ration) - Can be a 20% decrease in fresh cows (< 1 month)

 

Fiber

ADF	No less than 19% of the total ration
NDF	- 25 – 28% of the total ration (up to 30% for fresh cows) - 75% of ration NDF should be from forage

 

Protein

CP	Typically between 16 – 18%
DIP	No more than 67% of CP
UIP	At least 33% of CP

 

Minerals/Vitamins

Ca	0.7% of ration DM
P	0.3% of ration DM
Mg	0.3 – 0.4% of ration DM
K	1 % of ration DM
Se	Approx. 7 mg/day or 0.3 ppm of ration DM
Vit E	1000 to 3000 IU/day of ration DM (higher for transition cows)

Other trace minerals are approx. 50 – 150% of NRC

 

Lipids

• 4 – 6% of total ration (levels above this will decrease DMI)

 

Energy

• Not technically a nutrient but still a requirement
• No more than 0.8 Mcal/day deficit

 

Dietary Cation-Anion Balance

Production Level	DCAB range
Lactating Cows	250 – 350 mEg/kg
Dry Cows	-100 – 0 mEg/kg to prevent milk fever

 

Other things to consider

• Ideal forage is approx. 20% CP, 30% ADF, and 40% NDF
• Total Ration Dry Matter (for a TMR) is approx. 50% (between 40 – 60%)
• Forage to Concentrate Ration (F:C)
  
  • Dry cows and growing heifers can be 100% Forage
  • Lactating rations are typically between 40:60 and 60:40
  • Should not be less than 40% forage unless the level of management is very high

 

References:

Dairy Nutrition Primer Notes, Dr. Lissemore (2015)

Dairy Nutrition Elective, Ration Thumb Rates, Dr. Lissemore (2015)