First Green Grass of Spring - Not Enough to Supply Nutrient Needs of Grazing Cows

Turning cow herds out to graze pastures at the first sign of green grass harms forage growth later in the season. But there’s another big reason to wait, says a University of Missouri beef nutritionist.

Cows don’t benefit from early grazing as much as most herd owners believe.

Early grazing provides little quality and small quantity of grass, says Justin Sexten, Columbia. Herds need more nutrients than they get from early grass.

“Early pasture growth contains mostly water, only 25 percent dry matter,” Sexten warns. “Producers see this when they describe their cows as being ‘washy.’” Early grass has a high rate of passage through a cow’s digestive tract. In other words, don’t stand behind them.

After a hard winter, a cow nursing a calf needs extra feed until pastures are ready for grazing.

“With only 25 percent dry matter in the diet, a cow must eat 150 pounds of grass to meet her needs,” Sexten says.

A cow would walk constantly trying to find that much grass.

Quantity of growth at first green-up is minimal. “A cow can’t get a full mouthful of grass with each bite.”

The answer won’t appeal to farmers tired of winter feeding chores. Cows need continued feeding before grass grows large enough to supply nutrient needs. That means more hay and possible grain supplement.

Delayed grazing helps cows and pastures, Sexten says.

Rob Kallenbach, MU Extension forage specialist, agrees. “Grass that is nipped too short too early removes plant reserves needed for spring growth. Cool-season grasses stored sugar reserves in the lower stems last growing season. The reserves jump-start growth.”

Nipping too early removes reserves and the green leaves needed for photosynthesis. Early removal slows growth all season.

Early grazing makes a lose-lose situation, the specialists say.

Management may be more critical than usual this year as pastures recover from last summer’s record-breaking drought.

Sexten says to delay turning herds onto pasture until at least a 5-inch growth shows.

“Allow 2,000 pounds of dry matter per acre to accumulate,” he says. “Focus on the nutrient needs of the cows.”

A lactating cow’s daily nutrient demand equals 2.5 percent of her body weight. A dry cow requires 2 percent of body weight. Accurate cow-weight estimates are needed. Many producers underestimate how big their cows are when calculating feed needs.

Meeting nutrient demands may require buying more feed, or culling herd numbers.

Cows nursing a calf and preparing for rebreeding later this spring need nutrients. Cows with poor body condition scores are less likely to rebreed on time.

Spring-calving cow herds reach their highest nutrient requirements in April and May. Late snows delayed grass growth but brought moisture needed for that growth.

Both Sexten and Kallenbach advocate weekly or biweekly measurements of pasture dry matter growth and plotting the forage accumulation. That data guides the turn-in date for the next grazing paddock.

An MU website allows producers to enter their forage measurements to create a grazing wedge. Go to www.grazingbeef.missouri.edu.

The plant science and animal science specialists are in the MU College of Agriculture, Food and Natural Resources.

(By Duane Daily, MU Senior Writer)