The cost of producing hay drives many producers toward maximizing hay yields in order to distribute cost over more production. This often lowers forage quality because a more mature forage plant is being harvested. Supplementing lower-quality forages to meet livestock nutritional demands then adds indirect cost back to hay.
This is why we advocate cutting forages at the proper stage of maturity, based on species, to reach a compromise between yield and quality. What if you get your hay "cut right" but "baled wrong" (meaning baled at a too-high moisture content)? Obviously, one result could be that bales catch fire along with a storage facility, but this is not always the case. If you are pushing the moisture edge a little bit because you are trying to prevent leaf shatter or move on to another chore, you may not have realized that the hay was put up with extra moisture. What then happens to that bale after it sits in storage for a while?
Recently published work by Coblentz et.al., at the University of Arkansas looked at the effects moisture content has on quality characteristics of bermudagrass small square hay bales stored for a period of 60 days. Changes in temperature, dry matter content, nitrogen concentration, fiber concentration, visible mold and digestibility were evaluated.
In the study, Greenfield bermudagrass hay was baled at moisture content treatments of 17.8, 20.8, 24.8, 28.7 or 32.5 percent. Bales were weighed and sampled to determine initial moisture and nutritive content prior to placement in a storage facility.
As expected, higher-moisture bales had higher maximum temperatures and higher 30-day average temperatures than lower moisture bales (Table1). Combining higher moisture and temperature resulted in significantly greater mold ratings (on a 1 to 5 scale) and less dry matter recovery than lower moisture bales. Dry matter recovery was determined as a percentage of dry matter weights of bales before and after storage.
In assessing changes in quality (Table 2), bales made at lower moisture levels (17.8%, 20.8%) showed very little change in acid detergent or neutral detergent fiber (ADF, NDF), in vitro dry matter digestibility (IVDMD), nitrogen (N) or acid detergent insoluble nitrogen (ADIN-N) from pre-storage measurements. This would suggest that at these moisture levels little change would occur in forage intake, digestibility or protein content (N X 6.25 = crude protein). However, as bale moisture levels rose, ADF and NDF concentrations increased, digestibility decreased; total N increased slightly and ADIN-N increased when compared to pre-storage levels on a dry matter basis.
What's happening? With additional moisture of the bales generating heat, oxidation of non-fiber components such as non-structural carbohydrates results in higher concentration of fiber (ADF and NDF) and lower digestibility (IVDMD). Increases in NDF fiber (an indicator of intake) at the 32.5 percent moisture level are enough to reduce calculated daily dry matter intake by 1.77 pounds in comparison to pre-storage NDF fiber.
Oxidation and disappearance of non-structural carbohydrates would also explain the slight increase seen in N concentration of high moisture bales. A very interesting and important note is that the insoluble N portion (ADIN-N) increased with increased bale moisture. This portion of N is heat damaged and bound to acid detergent fiber, making it unavailable for animal use.
To summarize, make sure hay is dry enough to bale. If not, bermudagrass baled at moisture contents higher than 21 percent can have significant increases in fiber concentrations and insoluble N (heat-damaged N) and decreased digestibility. Similar effects have been reported for alfalfa hay as well (Colblentz et.al.,1996). If in doubt, test moisture content using the microwave method, moisture tester or some other means. As a side note, this effect is very similar to the weathering of round bales stored outside uncovered (Table 3).
This research was conducted at Purdue University by V.L. Lechtenberg and reported by M. Collins at the University of Kentucky. Changes that occurred in the weathered portions of round bales happened over a 5-month time period.
Colblentz, W.K., et.al., 2000. "Storage Characteristics and Nutritive Value Changes in Bermudagrass Hay as Affected by Moisture Content and Density of Rectangular Bales". Crop Science 40:1375- 1383
Colblentz, W.K., et.al., 1996. "Quality Changes in Alfalfa Hay During Storage in Bales". J. Dairy Sci. 79:873-875.
Collins, M., et.al., 1997. "Round Bale Hay Storage in Kentucky." Kentucky Cooperative Extension Service bulletin.