Dairy producers with alfalfa haylage and corn silage can maximize feed efficiency by feeding about equal amounts of both forages.
That's the conclusion from Glen Broderick, a research scientist with the U.S. Dairy Forage Research Center, Madison, WI. He and graduate student Andre Brito recently completed a study on the balance of forages in feeding programs.
“We fed various levels of alfalfa haylage and corn silage and monitored the results, including milk production,” says Broderick. “The cows did the best on diets in which the forage was about half alfalfa haylage and half corn silage. This was the place where feed efficiency — milk yield per unit of dry matter intake — was best without any loss of production.”
Twenty-eight cows were used for the 16-week trial. Four diets with varying amounts of the two forages were fed. The diets, labeled A, B, C and D, are described in Table 1. Other ration components included high-moisture corn, fat, sodium bicarbonate, salt, dicalcium phosphate, vitamins and minerals. As the amount of alfalfa haylage was decreased, soybean meal was added to balance the ration and ensure adequate crude protein levels.
Originally, Broderick included a diet with corn silage as the only forage.
“The cows didn't eat that ration very well,” he says. “Average intake dropped at least 10 lbs of dry matter/cow/day below the other cows, so we stopped feeding that diet.”
The overall crude protein percentage of all four diets was about 17%. The alfalfa haylage tested 24% crude protein and 38% NDF on a dry matter basis.
Table 2 shows the effects the diets had on dry matter intake, milk yield and rumen ammonia levels.
“As we moved from diets A through D, there were declines in dry matter intake, with the lowest intake recorded in the diet with the majority of corn silage,” says Broderick. “Reduced intake with increased corn silage may be due to its effect on rumen fill. Feeding alfalfa can give greater feed intake, because its fiber is digested rapidly and quickly leaves the rumen.”
As Table 2 shows, milk production was essentially the same for diets A through C. The slight increase for diet B isn't statistically significant, notes Broderick.
“There was a slight reduction in feed intake with diet C, but no decrease in milk production, so its efficiency was highest.”
Broderick and Brito also recorded the levels of rumen ammonia.
“Rumen ammonia gives you an indication of how much excess protein is being degraded in the rumen,” he explains. Those levels were 10.5, 10, 8.7 and 6.2 milligrams N/deciliter for the diets, moving from A to D.
“Clearly there was excess protein degradation on diets A and B,” says Broderick. “We don't know what the optimum is. There may not really be an optimum rumen ammonia for all situations, but 10-11 mg N/dl probably is in excess on this kind of diet.”
Broderick says he probably would have gotten the same milk production results if the haylage were lower in crude protein.
“But the rumen ammonia would have been lower with less crude protein in the haylage.”
|(% of Dry Matter)|
|Dry matter intake (lbs/day)||58.4||57.1||55.1||51.1|
|Milk yield (lbs/day)||91.5||92.6||91.5||87.1|
|Rumen ammonia (mg N/dl)||10.5||10.0||8.7||6.2|