Can cows eat too much grass?

This is dependent on many factors like the following:

• Type of bovine (i.e., Beef or Dairy? Lactating or dry? Pregnant or open? Breeding or feeder? Young and growing or old and maintaining weight?)
• Sex of bovine (i.e., bull or cow, steer or heifer)
• Body condition of bovine (i.e., thin or fat or normal?)
• Size and weight of bovine
• Age of bovine
• Length of grazing period
• Pasture quality (i.e., poor or Excellent)
• Moisture content of grass
• Nutrient quality of grass
• Soil quality
• Type of grasses grazed (i.e., tame or native and species)
• Climate
• Topography/geological factors
• Location

For this reason, we cannot answer this question. We can answer how much grass a bovine eats per day (see the related question below), but not how much per year.

However, in an ideal and perfect world, here is an example of how much a cow can eat per year:

One 1000 lb cow (dry, open) is on Meadow-Brome pasture that has an average moisture content of 70%. The average daily consumption of such a cow is 25 lbs of dry matter (DM) per day. And, there are 365 days per year.

Moisture content of grass:

Moisture content = 70%

Dry matter content = 100% - 70% = 30% / 100 = 0.3

Since we already know the daily consumption of the animal, we calculate the as-fed daily consumption value:

Amount of forage consumed per day (lb) on an As-Fed basis = 25 lb/day / 0.3 = 83.333 lb per day

Now we calculate the yearly as-fed consumption value:

83.333 lb per day x 365 days = 30,416.666 lb per year.

Thus, in an ideal world, a cow will consume under 30,500 lbs of grass per year. However this number varies considerably if you take in account all of the factors listed above.