If rainy weather left your forages lying in the ﬁeld too long, have them analyzed for neutral detergent ﬁber (NDF) before feeding.
Anytime harvest is delayed or forages are damaged by weather, forage NDF levels increase, and that can decrease feed intake, says Bill Weiss, dairy nutritionist at Ohio State University. As a result, you may need to decrease the amount of forage in the diet to keep the total forage NDF level within the target range of 18 percent to 21 percent of diet dry matter.
For example, if corn silage makes up 25 percent of diet dry matter and has an NDF level of 44 percent, it provides 11 percent forage NDF (0.25 x 44 = 11 percent). So, if your alfalfa contains 40 percent NDF, the diet should contain 25 percent alfalfa (21 percent total forage NDF – 11 percent NDF from corn silage = 10; 10 divided by 0.40 = 25 percent).