How do we determine Dry Matter Intake limits of stock?

Intake is often related to the neutral detergent fibre (a measure of the total structural fibrous fraction of forages). Neutral Detergent Fibre (NDF) is reported as a % of dry matter on feed analysis reports and as the NDF% increases, the amount of feed an animal can eat decreases.

How do we use the NDF% value to determine Dry Matter Intake (DMI)?

General Rule: 120 / NDF % of forage = % of body weight DM the animal can consume

Example: Vetch Hay with a NDF of 50%, How much hay can a 65kg ewe consume a day in the early pregnancy?

120/50 (NDF) = 2.4% of body weight as dry matter

65 kg x 2.4% = 1.6 kg Dry Matter /day

These ewes could consume up to 1.6kg of this feed on a dry matter basis. Assuming a Dry Matter % of 90%, this equates to about 1.8kg of hay as fed.

Note: This rule does not apply to stock in the later stages of pregnancy due to a reduction in rumen capacity from the growing foetus.

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