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Moo-Re Fibre Please, Say Cows

“Our concern is that in dairy rations, we have been feeding things that are too rich.”


Everyone talks about the benefits of sowing alfalfa to boost pasture yields.

But what about the upside to putting grass in a cow’s rumen?

According to Dan Undersander, a forage agronomist from the University of Wisconsin, there’s a lot of good that can happen with that alfalfa-grass mix, especially in dairy rations.

“While it’s been beneficial to grow alfalfa with grass mixtures, a lot of our dairymen have put a priority and a premium on pure alfalfa stands and it has made it harder for some of the hay growers,” said Undersander, speaking at the Hay Day workshop at AAFC Brandon last month.

“We think that actually now, with the amount of corn silage that’s being fed in dairy rations, that there’s actually a premium value to alfalfa-grass mixes compared to pure alfalfa.”

That works to the benefit of both the hay grower and the hay chewer, added Undersander, whose forage research experience spans three decades.

Twenty to 30 per cent grass in with an alfalfa stand makes the crop dry better than just pure alfalfa, and there’s also less risk of winterkill. Also, seeding a grass-alfalfa mix helps fields where low spots tend to get flooded out in spring. In such cases, the grass fills up those spots, he added.

The fibre digestibility of grass is roughly the same as in corn silage. That makes sense, he said, because corn is a grass species. But the problem in feeding too much corn silage in the diet is that the rations get too high in non-fibrous carbohydrates, which are the starches and sugars.

Feeding alfalfa to balance that out helps a little, but its effect is limited because alfalfa itself is high in sugars and starches, too.

Grasses, on the other hand, make a better fit because they offer anywhere from one-third to half as much non-fibrous carbohydrates as both alfalfa and corn silage.

“So, we see some value in replacing some of both the alfalfa and the corn silage in some of the dairy rations with grass,” he said. “Of course, we want to keep some of the alfalfa in that mixture, because we want the protein and other benefits of the alfalfa.”

Trials that looked at adding ryegrass to alfalfa silage to boost fibre – a common practice in warmer climates such as Britain and New Zealand – showed that it could be done without affecting daily milk production.

“Our concern is that in dairy rations, we have been feeding things that are too rich,” he said, adding that this is also true of beef cattle in feedlots.

Higher total fibre in grass mixes helps cows stay healthy, especially with the rich rations typically fed to dairy cows, resulting in lower culling rates, greater longevity, and less laminitis.

Feeding too rich feed, or a ration composed of up to 90 per cent grain, results in poor development of rumen pappillae, the fingerlike structures that line the rumen and absorb nutrients broken down by bacteria.

In young animals, rumen acidosis results when the diet contains too much non-fibrous carbohydrates.

Going from the old practice of feeding cattle corn and alfalfa to a ration composed of grain corn and a high percentage of corn silage with some alfalfa to round it out, is like feeding a human a handful of candy bars.

“If corn silage is 40 to 45 per cent grain, we’ve suddenly gone to what is effectively 60 to 70 per cent grain,” said Undersander.

“You know what happens when you eat too many candy bars? Well, all that starch gets rapidly digested and their stomach gets too acidic. It really is the same as if you or I ate six candy bars.”

Those rich diets are causing lameness in dairy cattle, he added. Some studies show 20 to 25 per cent of cattle in milking cow herds in the Midwest have foot problems, and 42 per cent of those cases are due to nutrition.

“We’re feeding too much grain and too little fibre,” he said, adding that the widespread introduction of corn silage in dairy rations may be the cause.

It’s only a slight exaggeration, said Undersander, to say that many high-grain feedlot beef rations will eventually kill a young animal in about a year.

“The animal will die if you don’t change the diet,” he said. “But if you introduce more fibre, you can bring it back.”

From the other perspective, too much fibre won’t be fatal, but it will affect performance. In contrast, if a yearling was fed a maintenance diet of 50 per cent TDN, it wouldn’t die, but it wouldn’t gain much weight, either. [email protected]

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