Two important pieces of information go into answering your question. One is the nutritional requirements of the cow. This depends on her body size, her reproductive status (pregnant or not, milking with calf at foot, or dry) and the weather conditions. A general rule for the amount of pasture intake measured as dry matter is 2.0% of the cow's body weight. So a 1,200-pound cow might need to eat 24 pounds of dry matter. Note that we talk in terms of dry matter because this is where the nutrition is, but the fresh pasture moisture content may be as high as 80%.
The second part of the answer is the amount of forage produced per acre and the quality of that pasture. Most improved pasture types have adequate quality, but some rangeland may not. Forage yields per acre vary with soil type, pasture species, fertilization practices, and weather, particularly rainfall. A related question is whether the pasture acreage will be grazed only or whether some of the pasture production will be used to produce hay.
As you can see, there is no simple answer to your question, but you can find more specific information by contacting your local Cooperative Extension office. Their telephone number will be listed in the government section of the telephone directory.
