Digestibility improves dairy cow production

The formula by which a dairy operation maximizes milk production is simple: When cows eat more alfalfa, they produce more milk. According to David Combs, professor of dairy science at the University of Wisconsin, striving for maximum dietary fiber in the forage is the secret.

“It’s all about digestibility,” Combs told producers at Alfalfa U in Twin Falls, Idaho. For example, alfalfa normally is about 42 percent digestible, with the range from 30 to 50 percent. “But 50 percent digestible is much more valuable than 30 percent,” he explained. “Thirty percent digestibility leaves a lot of milk on the table.” 

Combs suggested when dairy producers begin building the total mixed ration, they should begin with forage testing, the most important components of which are neutral density fiber, starch, protein and ash content. Be wary of how much ash is in the hay. “Anything over 10 percent concerns me. That tells me I’m picking up soil in the alfalfa bale,” he said. “Too much ash is like eating rocks. It won’t digest properly.” 

Producers should test for digestibility of forage, too. The TTNDFD (total tract NDF digestion) test, developed at the University of Wisconsin, predicts how a dairy cow performs when fed forages with different fiber digestion properties. But there are lots of forage tests, and growers need to pay attention to the results. 

“There is no one magic formula. But high producing dairy herds have managers that pay as much attention to their forage as they do their cows,” he said. “From harvest, to ensiling to feedout—they pay attention to the details.”

Combs said a typical dairy cow eats 15 to 17 pounds of NDF per day. If only 25 percent is digestible, that’s 4 pounds of NDF. If 70 percent is digestible, that’s 10.5 pounds of NDF. “That is highly digestible, which is less filling and allows the cows to eat more,” he explained. “The difference between the two is nearly 4 pounds of milk per day.” 

Quality hay is valuable

The researcher said dairy producers are typically forced to pay a premium for high-quality, high-fiber hay, but there is no way to capture that value. He said fiber digestibility is emphasized more and more with new varieties of forage. “You pay $300 per bag of seed and you need to be able to recoup the value on that,” he said. “Are you getting compensated for alfalfa that has high fiber digestibility?”

Fiber has value, he added. When hay prices are based on a relative feed value equation, as fiber increases, price is discounted. “But if alfalfa fiber is higher in digestibility, it can replace other fiber products,” he said. Alfalfa producers often use the Western Hay Market as a baseline for alfalfa hay values; Combs suggests growers can get paid based on fiber digestibility by using the TTNDFD test. “Pound for pound, alfalfa has more value than other sources of fiber,” he said.