Feeding more corn silage and less alfalfa haylage or hay can reduce the amount of manure and manure nitrogen a cow produces – without sacrificing milk production, according to research by Ohio State University dairy scientist Bill Weiss.

Weiss placed cows in stalls where they could be individually fed corn silage and alfalfa haylage or hay and the manure and urine weighed.

The average lactating dairy cow produces 140 lbs of manure a day, of which 85%, or 120 lbs, is water, with 40%, or 6 gallons, coming from urine. But urine output decreased greatly for cows fed diets that replaced haylage with corn silage. And that cut total manure. Cows fed corn silage as the only forage in the diet produced about 2.9 gallons less urine.

Why? Weiss believes it's because the corn silage diet had half the potassium. On average, corn silage contains 1.2% potassium and alfalfa, 2.5%.

Reducing nitrogen and phosphorus amounts in the manure was not directly correlated with cutting manure output, the research showed. Phosphorus is not affected by corn silage or haylage. Nitrogen excretion was reduced when more corn silage and less haylage was fed, says Weiss, and he expects average manure nitrogen to decrease by 5-7% if the diet moves from an alfalfa forage-containing diet to having corn silage as that forage.

A better way to cut nitrogen is to reduce crude protein, he says. Low-protein diets can still maintain milk production under experimental conditions, but, in the field, there's a chance of losing milk production if crude protein is cut.

If average-producing cows are fed the minimum crude protein to maintain production, higher-producing cows may not consume enough. So it's more profitable to overfeed protein and deal with the extra nitrogen in the manure. By not overfeeding phosphorus supplements and managing crude protein, producers can cut phosphorus and nitrogen amounts in manure.

Just don't replace too much hay or haylage with corn silage or you could end up with problems, advises Dan Undersander, University of Wisconsin Extension forage specialist.

"Research from the U.S. Dairy Forage Research Center has shown that maximum milk production occurs when at least 25% of our forage comes from alfalfa and 25% from corn silage. One of the major problems with feeding high levels of corn silage is that the ration must remain below 42% of non-fiber carbohydrates (NFC) to keep rumen acidosis down and milk production and herd health up."

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