When harvesting hay, generally our goal is to cut, rake and bale the crop so we are producing a leafy, palatable stored forage that will get our cows and other livestock through the winter in the best possible condition. In visiting with hay producers this summer, I have heard several times that the rain we received this summer has complicated hay harvest tremendously. Rain is necessary for our forage crops to grow, we all know that. But to harvest hay in the best conditions, rainfall can certainly cause problems. Rain washes away the highest quality, most digestible portion of the curing forage plant - the soluble proteins and sugars. Furthermore, the impact of a raindrop can shatter leaves (the highest quality and most digestible portion of the forage plant) and the leaves are left lying on the ground when we are finally able to bale. If we rush the baling process and the bale is too wet, the hay will go through heating (binding up the sugars and proteins making them indigestible - this occurs when we have caramel smelling hay) and produce mold (the mold spores consume the soluble sugars and proteins leaving us a dusty, low-quality mess). Because of all these concerns, several producers indicated that the first cutting of some of their hay meadows was harvested in late July or early August.
As forage matures, protein content of our warm-season grasses will decline slightly, but neutral detergent fiber (NDF) and acid detergent fiber (ADF) will increase dramatically. The NDF and ADF content is what determines the digestibility of the forage, and as it increases, energy content and hay intake decrease. High fiber forages (forages with high levels of ADF and NDF) are harder for the microbes in the rumen to break down and thus stay in the rumen longer. Because these forages are in the rumen taking up space for a longer period of time, intake and digestibility of the forage declines as fiber goes up. Unlike many other hay-producing areas that produce large amounts of clover or alfalfa hay, Arkansas production is dominated by perennial grasses (mostly tall fescue, bermudagrass, or bahiagrass). Leaf shatter is a big concern with legume hay and other leaf grass crops (like orchardgrass), but this is a minor concern with most of our hays. So, hay quality of a particular forage is determined more by harvest interval than almost any other management factor we control.
A well-managed bermudagrass hay field (fertilized and cut on a 28-day interval) will produce hay that is 12 to 14 percent crude protein and 60 to 62 percent total digestible nutrients. This quality of hay will be adequate for beef cows in any stage of production with no supplemental protein or energy. Research at the University of Arkansas in Fayetteville indicated that a rainfall event (3 inches) on bermudagrass that has reached 13 percent moisture (ready to bale) will have little effect on the protein content of the resulting hay when it is finally ready to bale again but will increase neutral detergent fiber by 1.5 percentage units and increase acid detergent fiber by 2 percentage units; this decreases the TDN content of the hay by 1.5 percentage units. But what if we were to wait for a rain and allow the hay to grow more, wouldn't that be a good thing all the way around? We are increasing yield and not getting the hay rained on if we wait 14 more days (to a 42-day harvest interval) and allow this same bermudagrass to grow longer. Protein declines and the fiber increases. This decreases the TDN by 6.5 percentage units from 64.0 to 58.5 percent (this quality of hay would be fine for most cows even those that have a calf). If we delay another two weeks, we lose 15 percentage units of TDN and have hay that is frankly not worth baling (8 percent crude protein and 44 percent TDN, which will not meet the requirements of many animals).
Even a short delay in harvest of our warm-season grasses will have more negative impact on hay quality than a single rainfall event (this research looked at rains of 0.5 to 3 inches with similar results). Since a delay in harvest of one cutting will delay the harvest of the next cutting, it can be said that a long delay not only decreases the quality of this harvest it also impacts on the yield and quality of the next harvest. Dry matter loss from the rained on bermudagrass was only about 2 percent, where DM loss of orchardgrass was four-times greater. Leaf loss and loss of soluble sugars and proteins from burmudagrass is negligible, while these losses are a much greater concern with other forages. The warm-season grasses we rely on for hay in Arkansas really do not have much soluble sugars and proteins to lose and leaf shatter is minor. In summary, it is probably better to harvest at the right time than have a long delay in harvest, but if hay does get wet, it is probably better to let it dry completely than bale early (at too high moisture content) and deal with heating (caramelization and fire concerns) and mold issues.