Balancing the diet

A dairy cow diet needs to be balanced to achieve milk production, body condition and reproduction targets. The major factors to consider are:

  • dry matter (DM)
  • neutral detergent fibre (NDF)
  • starch
  • sugar
  • protein.

Keep the diet consistent to optimise microbial production (more rumen microbes equals more milk) and to achieve the desired milk composition targets.

Diet targets - rules of thumb

Table 1. Rules of thumb for maintaining a balanced diet
Dietary element Intake level
Dry matter intake Minimum daily intake equivalent to at least 3% of body weight, 4% for higher-producing cows (over 30 L/day)
Neutral detergent fibre (NDF) Maximum daily intake equivalent to 1.2% (1.3% for high producers) of body weight in total diet
Maximum 1% of body weight from forage
NDF content of the total diet 28-32% NDF in diet DM for cows producing over 9000 L
30-34% NDF for late lactation/medium production
34-40% NDF for cows producing under 6000 L on tropical pastures
Effective NDF (eNDF) Minimum 20% of total NDF as eNDF (forage length 2-5 cm)
Non-fibrous carbohydrate (NFC) 35-40% of diet DM at peak/high production
32-37% at late lactation/low production
Starch 22-25% of diet DM
Sugar 3-6% of diet DM (up to 10% sugar tolerated on mature tropical grass/molasses diets)
Crude protein (CP) Minimum 16% of diet DM at peak/high production
Minimum 13% at late lactation/low production
Rumen-degradable protein (RDP) 66-72% of the CP content of the diet at peak lactation/high production
70-76% of the CP content of the diet at late lactation/low production
Rumen-undegradable protein (RUP) Formulate to supply lysine and methionine at a 3:1 ratio
Fats Maximum 5-6% of diet DM

Dietary minerals and vitamins

  • Calcium (2% of diet DM)
  • Copper
  • Phosphorus
  • Cobalt
  • Potassium
  • Zinc
  • Sodium
  • Manganese
  • Magnesium
  • Selenium
  • Chloride
  • Iodine
  • Sulphur
  • Iron
  • Vitamin A, D, E, K.

Nutrient content of feeds

In order to balance the diet correctly, it is essential to check the DM content and nutrient composition of all the feeds that you currently use and any alternative feeds that may be available. There are two main ways of obtaining the DM% and nutrient composition of your feeds:

  • Determine the DM% and analyse the nutrient composition of your feeds on a regular basis through feed sampling and testing.
  • Use DM and nutrient composition values from feed analysis tables (refer to the Feed Plus CD or the Protein Plus checkbook).

Meeting intake and nutrient targets

1. Determine DM intake (kg)

If total DM intake is unknown, use the rules of thumb for DM intake and maximum NDF% from the list above.

Example

A 600 kg cow will need at least 18 kg of DM per day.

Example calculation for DM intake

Daily DM intake: 600 kg × (3% ÷ 100) = 18 kg DM/day

2. Estimate or calculate daily DM intake of individual feeds (kg)

The DM intake of some feeds (such as grain, molasses, hay and silage) can be calculated by weighing the amount offered per cow, and then use their DM% to calculate the DM intake of each feed. To estimate pasture intake, subtract the known intakes of concentrates, hay and silages from estimated total  DM intake.

Example

600 kg cow fed:

  • 6.7 kg grain as-fed (90% DM)
  • 13.3 kg maize silage as-fed (30% DM)
  • kikuyu pasture.

Example calculations for DM intake for individual feeds

Grain DM intake: 6.7 kg as-fed x (90% DM ÷ 100) = 6 kg DM/day.

Silage DM intake: 13.3 kg as-fed x (30% DM ÷ 100) = 4 kg DM/day.

3. Calculate daily nutrient intake

For each feed, use the DM intake of each feed (calculated in step 2), plus their nutrient values (from your own analysis or feed tables), to calculate the intake of each nutrient from that feed in kilograms. Add the nutrient intakes from each feed to calculate total daily intake for each nutrient.

Example

600 kg cow fed grain, maize silage and kikuyu pasture. Crude protein (CP) in feed DM:

  • 12% grain
  • 8.6% maize silage
  • 23.2% kikuyu.

Example calculations for CP intake

CP intake of individual feeds (grain): (12% ÷ 100) x 6 kg DM intake = 0.72 kg CP from grain.

Total diet CP intake: 0.72 kg from grain + 0.34 kg from silage + 1.86 kg from kikuyu = 2.92 kg CP/day.

4. Check if the ration meets diet targets

For each nutrient, divide the total daily intake (kg) of that nutrient (calculated in step 3) by the total diet DM intake (from step 1), then multiply by 100 to calculate the nutrient % in the total diet. Then check your values against the target values listed above. Diet target is a minimum 16% of  diet DM for high production. Repeat for each nutrient.

Example

600 kg cow on grain, maize silage and kikuyu pasture with:

  • CP intake = 2.92 kg
  • total DM intake = 18 kg.

Example calculation for determining if diet targets are being met

CP% in diet: (2.92 ÷ 18) × 100 = 16.2% CP in total diet