Fiber ‘and’ digestibility critical to dairy grazing

DALTON, Ohio — Just a few days is all it takes for the nutrient value of a pasture to change and cost dairy graziers a lot of money.

During a feature presentation Jan. 23 at the North Central Ohio Dairy Grazing Conference, Geoff Brink, a forage research agronomist at the U.S. Dairy Forage Research Center in Madison, Wis., talked about those changes and how to make the most out of grazing.

Brink focused on two factors: Neutral Detergent Fiber (NDF) and Neutral Detergent Fiber Digestibility (NDFD). Both are important to having a balanced feed source, and both determine the health and productivity of a dairy cow.

Brink said NDF is measured by boiling down the feed in a detergent, and what is leftover is the NDF — the fibers that would be left in a cow’s stomach.

Plant cells

With most forage crops, the stem and cell wall is the most fibrous part, while the leaves and the inner parts of the cells act as energy. Cows need both to do well, and both can change rapidly at different parts of the growing season.

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The biggest change usually happens in the spring, Brink said, often in the first three weeks of May. During this time, the plant is maturing and rapidly producing a stem. If allowed to over-mature, fiber will go up and milk production will go down considerably.

Falling behind the grazing schedule by only three or four days can result in an increase in neutral detergent fiber of 3 percent, while fiber digestibility falls 4 percent.

Cow intake and production goes down, and producers can easily lose 8 pounds of milk per cow, per day.By the numbers. While this may not seem like a big loss on a couple cows, the cost multiplied by a herd of 60 cows would be a loss of 480 pounds of milk. Using a sale price of roughly $20 per hundred pounds of milk, producers would lose nearly $100 a day.

Brink said when graziers fall behind, it’s hard to catch up, because the grass in each subsequent pasture they move their cattle into will likely be just as mature, or even over-mature.

“Those effects keep accumulating until you’ve gone through all of that mature grass,” he warned.

Add legumes

In addition to staying on top of the grazing schedule, he recommends producers develop a mixed stand in their pastures. They should have grasses, but also a third or so of legumes.

The neutral detergent fiber of an all-grass pasture is usually 45-50 percent, but if a third of that pasture is legumes, the cow will eat more and produce more.

“If you have a pasture, you must have legumes in it to make money,” he said.

Adding legumes to the pasture brings down the fiber and increases digestibility. Popular legumes include white clover (about 25 percent NDF), red clover (about 30 percent NDF) and alfalfa (about 35 percent NDF).

Graziers can also add some grain to their cows’ diets, which is low in fiber and almost entirely digestible. Corn grain, for example, has only 10 percent NDF.

Brink said if there’s ever a time to delay grazing, the best time is in the fall, because fiber and digestibility change less rapidly.