Feeding corn silage instead of alfalfa haylage or hay can reduce the amount of manure a cow produces as well as its nitrogen content.

After 10 years of research that included 14 experiments and 55 rations, Ohio State University dairy scientist Bill Weiss has quantified how realistic it is for producers to strive to reduce manure output, along with phosphorus and nitrogen, without sacrificing milk production. It's a matter of efficiency.

“If you get less manure and the same amount of milk, cows are using the feed more efficiently,” he says.

Cows were placed in stalls that allowed them to be fed individually and the manure and urine to be weighed. The predominant forages fed were corn silage and alfalfa haylage or hay. By feeding corn silage instead of alfalfa, Weiss found that manure volume could be reduced without hurting milk production.

He also found that 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.

Replacing haylage with corn silage significantly decreased urine output, which cut total manure. Cows fed diets in which the only forage was corn silage produced about 2.9 gallons less urine.

The likely cause of this reduction was less potassium in the ration. On average, corn silage has about half as much potassium as alfalfa — 1.2% vs. 2.5%.

The studies showed that reducing the amount of nitrogen and phosphorus in the manure was not directly correlated with cutting manure output. Neither corn silage nor haylage had an impact on phosphorus. The only correlation with how much phosphorus came out of the cow was how much went in. Phosphorus, naturally found in feed, is also fed as a supplement.

“Feed phosphorus to a minimum,” Weiss recommends. “That's as efficient as you can get.”

Nitrogen is trickier. “By feeding more corn silage and less haylage, nitrogen excretion is reduced,” says Weiss. “The effect of switching forages is statistically significant but small. On average, going from a diet with all the forage from alfalfa to one with all the forage from corn silage, we would expect average manure nitrogen to decrease by 5-7%.”

A better way to cut nitrogen is to reduce crude protein.

“Under experimental conditions, where we usually have good control measures, we can feed pretty low protein diets and still maintain milk production,” Weiss says. “In the field, there is a risk of losing production if you cut crude protein.”

If average-producing cows are fed the minimum crude protein to maintain production, higher-producing cows may not consume enough. Thus, it's more profitable to overfeed protein and deal with the extra nitrogen in the manure.

In conclusion, Weiss says, “Feeding a ration for which the forage portion is predominately corn silage will reduce the total amount of manure. There will also be a small decrease in the amount of nitrogen excreted with no effect on milk production.”

Moreover, by not overfeeding phosphorus supplements and managing crude protein, producers can further decrease the phosphorus and nitrogen in manure.