Many state dairy farmers are waiting a bit too long to chop corn for silage, and that”s hurting their milk checks. The latest research at the University of Wisconsin-Madison shows that chopping at 65 percent moisture will maximize milk and milk protein yields, according to Randy Shaver, a dairy scientist and extension dairy nutritionist at the College of Agricultural and Life Sciences.

When Shaver summarized data from forage testing labs in Wisconsin, he found that state farmers tend to chop corn silage at an average moisture of 58 percent. “We recommend 65 percent moisture from the standpoint of silage preservation and recovery of dry matter and energy from the field and silo. I thought one reason we weren”t seeing that moisture is because we don”t have good information on the feeding value of corn silage at that moisture content, so I looked at how cows responded to silage at different moisture contents,” Shaver says.

“This study showed that 65 percent moisture is also for best milk production, protein yield and nutrient digestion. So no matter how you look at it, that”s the target to shoot for when you harvest corn silage,” he says.

Keep an eye on milkline movement, Shaver recommends. There”s no reason to start chopping while corn is in the dent stage, before the milkline moves. Start harvest when the milkline is at 1/4 milkline, and try to finish by 3/4 milkline. By black layer stage, the corn is too dry and starch digestibility is down. From 1/4 milkline to 3/4 milkline should give you a two to three week harvest window in a typical summer, according to Shaver.

CALS researchers measured digestion of silage for 28 days in 20 mature Holstein cows in the UW-Madison herd. The silage was grown at the Arlington research station and stored in silage bags. Diets contained 50 percent forage (67 percent corn silage, 33 percent alfalfa silage) and 50 percent concentrate (shelled corn and soybean meal based). They were formulated to contain 18 percent crude protein, and fed once daily as total mixed rations. Dry matter intake was about 3.75 percent of body weight.

Corn silage maturities were early dent (70 percent moisture), 1/4 milkline (68 percent moisture), 2/3 milkline (65 percent moisture), and black layer (58 percent moisture).

Milk yields were 2.2 pounds per day and protein yields 0.11 pound per day higher for 2/3 milkline compared with early dent. There were no differences in milk yield between 1/4 milkline, 2/3 milkline and black layer. This suggests some flexibility in harvesting corn silage between 1/4 milkline and black layer. However, milk protein yield was .08 to .11 pound per day higher for 2/3 milkline, compared with 1/4 milkline and black layer, Shaver points out.

Going from 2/3 milkline to black layer, starch digestibility of the diet fell from 92 percent to less than 88 percent. Intake of digestible starch and digestibilities of organic matter and acid detergent fiber were also lowest for black layer. This drop in starch digestibility could translate into lower milk yield or lower weight gain in a longer term feeding trial or in higher producing cows, he says.

Milkline isn”t a perfect indicator of dryness, Shaver notes, because moisture content at a given milkline can vary due to environmental and hybrid variations. For now, he suggests using milkline as a guide, but using a moisture content assessment as your main trigger for when to begin harvest. Contact your county Extension office for information about using your microwave to determine corn moisture content.

Graduate student M.A. Bal and agronomist Jim Coors also worked on this study. Coors, a frequent collaborator on silage studies, deals with corn from seed to harvest, while Shaver takes over from harvest to bulk tank.