Our mechanical forage harvest season has begun. Forages are mechanically harvested for use as stored feed. We have 3 basic forage harvest systems that are used: dry hay, silage, and wet hay or baleage. Within each of these harvest systems there are some principles or guidelines that should be considered and followed to minimize losses and keep forage quality as high as possible. I'll summarize these harvest guidelines from a forage harvest presentation given by Bill Weiss, OSU Animal Sciences Department at a meeting this past winter.
The first principle that needs to be understood is forage maturity determines forage quality. Forage quality declines as the forage matures and fiber content increases. This quality decline is particularly pronounced during the spring first cutting harvest as plants shift from vegetative to reproductive growth. A second principle of mechanical forage harvesting is that there are losses at every step beginning at mowing and continuing through storage and feeding. For example, respiration losses continue from the time the plant is cut until it dries down to a moisture content somewhere around 40 to 45%. Dry matter (DM) losses from respiration average 2-4%, but in slow drying conditions could be doubled. Rain damage can account for further DM losses ranging from 0-25% depending upon the timing and the quantity of rainfall. Then there are DM losses associated with the harvest process of rakin, tedding and baling or chopping. An average loss range is 2-10%. The drier the forage is when handled the higher those leaf shatter losses will be.
The maximum safe moisture content of dry hay depends upon the type of bale, whether or not a preservative is used and time of year the forage is baled. Hay can be baled wetter in the fall when ambient temperatures are cool and are going to stay cool. Since we are looking at hay production at the beginning of our harvest season, we need to consider moisture contents that will allow hay to go through the summer in good condition. If preservatives are not used then the maximum safe moisture for small rectangular bales is 20%, for large round bales is 15-16% and for the large rectangular bales is 13-15%. If forage is baled wetter than these percentages there will be mold growth and heat generated. This results in stored forage that will have lower energy, lower available protein and often dry matter intake is lower when feeding these forages. In severe cases of baling at too high a moisture content when hay is stacked, spontaneous combustion can occur.
If hay preservatives are used keep the following guidelines in mind. The most effective preservatives are propionic acid based. No preservative product is effective at greater than 30% moisture and most are iffy between 25 and 30 percent moisture. When used at less than 25% moisture, these products can allow you to bale hay and will provide protection against mold and excessive heating. To get this protection the preservative must be applied uniformly within the bale and at the correct amount. Recognize that because these products are volatile in nature, as they dissipate, their effectiveness in preventing mold decreases. In other words, if these higher moisture bales do not dry out in storage, they have a "shelf life" that limits how long they can be stored as a quality feed.
Baleage is a forage production system that combines baling with ensiling. In this system, hay is baled at higher moisture contents so the risks of losses from rain and leaf shatter are reduced. In order to avoid the mold and heating damage that would normally would occur at these higher moisture contents, the bale must be wrapped in plastic to exclude oxygen and allow ensilingbto take place. Some guidelines to pay attention to in this system include:
- Forage should be baled at between 40 to 60 percent moisture
- Consider the use of a liquid lactic acid bacteria inoculant applied at baling to lower fermentation losses
- Wrap the bales quickly after baling, immediate is best but certainly within 12 hours of baling
- Use enough plastic to wrap, generally 4 layers of 1.5 mil plastic
- Recognize that the lifespan of wrapped bales is limited, practice a first made, first to be fed management
Sometimes concern is expressed about the possibility of listeria with baleage. Listeria is a risk in any ensiled system where the forage pH is greater than 5.0. When the pH of the ensiled forage is below 5.0 the risk of listeria is very low.
Forage silage production involves chopping the forage at 30-40% dry matter, putting it into either an upright or horizontal silo and letting the fermentation process take place. The benefits are that once again some leaf shatter losses and potential rain losses can be minimized. On average, silage quality tends to be higher than hay because these losses are minimized. To make this system work effectively the forage must be harvested at the correct dry matter content, the chop length must allow for good packing of the forage in the silo, the forage must be packed tightly to exclude oxygen, and any new oxygen must be prevented from entering the silage mass by sealing quickly and completely.