A number of different factors determine the daily intake of a cow, the University of Nebraska's Rick Rasby writes at beef.unl.edu/. The beef specialist lists the primary factors as cow weight, forage or diet quality, and production stage.

Cows weighing 1,300 lbs. will consume more on a daily basis than lighter-weight cows weighing 1,100 lbs., he says, while lactating cows will eat more feed than non-lactating cows. Intake also is different for cows in early lactation compared to those in late lactation.

He provides these "thumb rules" to help estimate daily feed intake of gestating or lactating cows on a dry matter (DM) basis consuming forages of differing quality:

  • When forage quality is low -- total digestible nutrients (TDN) of 52% or less -- non-lactating cows will consume 1.8% of their weight DM basis.
  • If forage quality is average (TDN of 52% to 59%), non-lactating cows will consume about 2% of their body weight daily DM basis, whereas a lactating cow will consume about 2.3% of her body weight daily an a DM basis of the same forage.
As an example, if the forage were 55% TDN and lactating cows on the average weigh 1,200 lbs., they'd eat about 28 (1,200 lbs. x 0.023) lbs. of hay daily on a DM basis. If the hay were 88% dry matter, on an "as-fed" basis, cows would eat about 32 (28 lbs./.88) lbs. daily. If there were 200 head of cows in the herd, it would take about 3.2 tons of this hay/day [(200 head x 32 lbs./head/day)/2000 lbs.] not accounting for any waste.

Taking the use of feed intake one more step, Rasby says a 1,200-lb. cow, the first 90 days post-calving and producing 20 lbs. of milk at peak milk production, needs to consume 2.7 lbs. of protein/day on a DM basis. If the hay is 8% crude protein and the cow eats 28 lbs. of hay DM, she will eat 2.24 lbs. of protein (28 lbs. x 0.08). This hay will need to be spiked with some protein to meet her post-calving protein requirement.

Likewise, if she needs 16 lbs. of TDN daily, then 28 lbs. of a forage that's 55% TDN yields 15.4 lbs. of TDN consumed. This forage will need to be spiked with some energy. A small amount of a good-quality alfalfa could fit the need.
-- Rick Rasby, University of Nebraska