Dairy producers know that estimating each cow's daily feed intake can be difficult. But for those who graze their herds, the task is even more ominous.

“It's one of the most challenging aspects of grazing management,” says Larry Muller, a Penn State University dairy nutritionist. “That's because the amount of dry matter available per day changes as the season progresses and pasture growth slows, greatly affecting intake and milk yield.”

Lactating dairy cows should eat about 4% of their body weight in dry matter daily, says Muller. Beef producers grazing stocker cattle should aim for daily dry matter intakes equaling 3% of body weight, adds Garry Lacefield, University of Kentucky extension forage specialist.

Several inexpensive tools are available to help graziers get a handle on pasture quantity. Wire cages, sward sticks and rising plate meters can provide fairly accurate estimates of the forage available per acre, says Lacefield. Then some simple calculations can be used to determine the size of the paddock or pasture that's needed each day.

Dennis Johnson, a University of Minnesota dairy scientist, uses 2'-square wire cages, or exclusion areas, to calculate forage availability after cows have grazed a paddock. But they can also be used before it's grazed.

“I periodically put several of them on the paddocks where the cows are grazing,” Johnson explains. “After they've finished, I clip the forages in the exclusion areas to the same height they were grazed and then dry those samples. Next, I calculate back to an acre basis the amount of dry matter that was consumed and divide by the number of cows.”

Rising plate meters and sward sticks both measure average plant height. Many fencing equipment suppliers carry these tools.

Your own experience is another good resource, says Lacefield. “Once producers get involved with grazing, they can use their eyes to estimate how much pasture is needed for a specific number of cattle over a certain number of days.”

You also must know the pasture's quality in order to supplement the ration properly. Minnesota's Johnson encourages each grazier to take scissor cuttings or grab samples that simulate grazing and send them to a forage-testing lab for analysis.

“There are labs in this state that will fax test results back within 24 hours of receiving the samples,” he says.

Take samples at several locations throughout the pasture, mix them and send a composite sample to the lab.

“Take your scissor cuttings at the height that's typical of how the animals graze,” Johnson advises. “If they don't graze all the way to the ground, don't cut it all the way to the ground.”

Take Intake Times Two

Dairy cows must have sufficient pasture in order to maintain feed intake and milk production, says Larry Muller, a Penn State University dairy nutritionist.

A drop in daily pasture intake will result in an immediate drop in production, he says. In a recent Penn State study, cows had access to 100 lbs of pasture dry matter/cow/day. They ate 7 lbs more dry matter and produced 6 lbs more milk than cows supplied with 60 lbs/day of pasture dry matter.

Pasture was the only feed provided. But the same relationship held when cows were fed supplements.

“The bottom line is that the pasture available/cow/day should be about twice the expected pasture dry matter intake if you want to maximize intake and avoid big drops in daily milk yield,” says Muller.

For example, if a herd of 50 cows is estimated to need 30 lbs of pasture dry matter/cow/day, then 60 lbs/cow need to be available. That's 3,000 lbs for the 50-cow herd. If 2,000 lbs of dry matter are available per acre, 1½ acres need to be allocated for the 24-hour period.