By Dan Undersander
Getting hay dry for baling is always a problem at this time of year. Hay baled too wet will heat and may burn. More commonly, the heating will result in no fire but loss of digestible protein and, especially total digestible nutrients. The TDN loss has been underrated. Fifty percent of samples submitted to forage testing labs in the Midwest have lost 4 or more points of TDN due to heating with some losing as much as 16 points TDN.
The two most important factors for drying hay are to condition properly and to put hay into a wide swath covering at least 70% of the cut area immediately after cutting. The conditioner should be adjusted for each field (based on crop, cutting and yield) so that 1 to 5% of the leaves show some bruising. Remember that conditioning is for drying stems and a wide swath for drying the leaves. Over 50% of the water to be lost in drying is in the leaves. It is better to drive on a wide swath than to make a narrow windrow (fitting between the wheels) since the narrow windrow will have greater respiratory loss of starch and sugars and longer drying time.
Hay must be baled hay at less than 16% moisture to avoid heating unless some special precautions are taken. If hay must be baled wetter to avoid rain consider the following:
Use a preservative. Any preservative containing a high percentage propionate (propionic acid) will be effective. Use of ammonium propionate (also called buffered propionic acid) rather than propionic acid is recommended because the product is less caustic - therefore safer to handle and less corrosive to machinery. A minimum of 8 pounds of propionic acid per dry matter ton of hay is required for preservation of wet hay (see figure 1). When purchasing preservatives, compare cost on a per pound of propionic acid basis. Other additives do little if anything to preserve hay. Hay preservative products that dilute the propionic acid require greater product use rates.
Consider wrapping the bales in plastic (at least six layers). Eliminating the oxygen stops respiration and heating. The advantage of wrapping in plastic is that any moisture of hay can preserved from 20% to 70%. Wrapping should occur immediately after baling and use of six layers of plastic to exclude oxygen is crucial. Wrapping can be either individual or in a tube. Plastic must be inspected periodically and any holes sealed with tape. Fermentation will occur if bale moisture is over 50% and be greatly reduced below that moisture.
Make smaller bales. Smaller bales have greater surface area to volume ratio. Therefore heat loss is greater and temperature buildup in the bale is less. Therefore the following will reduce TDN loss from heating:
•Small square bales (14-inch by 3-foot) can be loosely staked to allow some ventilation and drying.
•Larger bales (round or square) bales should be not be stacked for a 7 to 10 days to allow the heat loss from the bale.
•Make smaller big bales if hay must be baled wetter than 16% moisture, e.g. a 3 foot diameter round bale rather than 5 foot diameter or a 4 foot long medium square bale rather than 5 foot long bale.
•Bales made in cooler weather lose heat more rapidly than bales made over summer when air temperature is higher.
In summary, heating damage is more prevalent in hay and haylage than many realize. It causes losses in protein availability and TDN. The TDN loss is becoming more significant with higher grain prices. Proper management can increase hay drying rate and reduce heating in baled wet hay.
Undersander is a University of Wisconsin Extension forage agronomist.