Barry Bradford, Kansas State University dairy nutritionist, said traditionally when people think about feeding dairy cattle they think a certain way.
“We feed forage for cow health, to keep the rumen healthy and we feed concentrates for energy,” Bradford said. “If you actually do the math, that’s not really accurate.”
In typical United States dairy rations, forages supply at least a third of the energy. Bradford believes this is limiting.
“Usually the limiting constraint on a dairy cow genetically today is going to be how much energy you can get through her system with without disrupting her gut,” he said. “So energy is a big deal on these animals.”
Depending on how dairy farmers feed, the cow’s energy needs are a result of forage digestibility.
“Not only because we want every mouthful to deliver as many calories as possible, but also because if that mouthful is poorly digestible its going to basically sit in her gut longer and make her less hungry,” he said.
Bradford believes it’s necessary to understand fiber tests in order to produce the best forage possible. Dairy nutritionists want a feed forage to be low in lignin to get the best possible dairy ration. Yet, lignin isn’t the whole story.
“We don’t know exactly what determines other components of digestibility and 20 years ago we were just trying to measure lignin straight up,” he said.
This caused two problems in the lab: it’s extremely difficult to do accurately and it’s expensive.
“We’ve gotten to the point where we say we’re just better off testing how well microbes can digest this fiber rather than trying to quantify all the chemicals that might determine that,” he said. “Let’s just measure how well microbes can break down a particular fiber source.”
Ordering lab tests can be confusing and hard to decipher. Tests using microbes digesting the powdered forages are a little tricky, but can be helpful.
“I’ll give you my perspective, which not everyone would agree with,” Bradford said. “The point I want to make is these test tube cows are really useful. I also think we have to keep it in perspective.”
Forage in the diet of dairy cattle serves a purpose. The long particles “scratch” the rumen to keep it healthy. The test tubes require powdered forages and it’s hard to justify spending the extra money on some of the lab tests.
“When you feed the animal she’s ingesting these big particles, she has to chew it. She has to ruminate it, which is going to affect how quickly it breaks down. The pH in her rumen is affected by this. How quickly it flows out of the rumen.
It’s way more complicated than those test tubes, Bradford said. Picking a test to compare apples to apples across the board becomes more helpful in the end.
“I think the biggest value of these assays is actually targeting forages,” he said. “If I were working with a big dairy I would be trying to find super high quality forages and target them to super high producing cows because they can go crazy with really good forages.”
Lower producing cows don’t tend to respond as much as the higher producing ones. They tend to get better digestibility but they don’t increase intake, which results in less milk.
The bottom line is dairy nutritionists want cows to eat a lot so they push a lot of milk out of the system and more digestible fiber helps cows do that.
Kylene Scott can be reached at 620-227-1804 or [email protected].
