For the majority of dairy farms in the U.S., corn silage supplies a sizable portion of both digestible fiber for the dairy herd as well as providing about a quarter of cows' energy needs. Approximately 50 percent of the energy value in corn silage comes from the starch found in the corn kernels. Improving starch and fiber digestibility in corn silage often will improve milk production as well as reduce feed costs. Corn silage production and management should be a top priority for the dairy farmer.
The primary goal of ensiling a corn crop is to preserve it for future use as a feedstuff for livestock. The ensiling process essentially preserves organic matter in an air-free environment and keeps it from spoiling. The plant material - usually the entire corn plant including the mature ears - undergoes a fermentation process in which bacteria produce acids that "pickle the pile". The rapid removal of oxygen by a limited amount of oxidation and the physical packing of a silo or bunker are critical in producing a well-fermented and stabilized pile of corn silage.
However, the most critical aspect of making top-quality silage is the moisture level of the corn at harvest time.
A paper published by the American Registry of Professional Animal Scientists (ARPAS) in the spring of 2012 summarized a number of key characteristics of corn silage that can affect its milk producing potential.1 The authors investigated dry matter content (DM), kernel processing (PROC) and theoretical length of cut (LOC). They pulled together data from 27 trials reported in 24 papers published between 2000 and 2011 in the "Journal of Dairy Science" or "Animal Feed Science and Technology."
As corn matures in the field the dry matter increases. Another way of describing this is to say that moisture levels decrease as corn matures. The corn silage maturities in this analysis were expressed in terms of DM content at feed out from the silos and were put into five categories for the analysis:
≤28 percent (VLDM) very low dry matter
>28 to 32 percent (LDM) low dry matter
>32 to 36 percent (MDM) medium dry matter
>36 to 40 percent (HDM) high dry matter
>40 percent (VHDM) very high dry matter
There were three categories for kernel processing treatments for the analysis:
1 to 3 mm
4 to 8 mm
There were six LOC treatment categories for the analysis:
.48 to .64 cm
.93 to 1.11 cm
1.27 to 1.59 cm
1.90 to 1.95 cm
2.54 to 2.86 cm
The resulting analysis of all the data concluded that the delayed harvest and the consequential increase in DM content of corn silage reduced starch digestibility. Milk yield decreased, on average, more than 4 pounds per cow per day when corn was harvested at VHDM. In other words, when the DM of corn climbed above 40 percent, the less milk it was capable of producing due in part to poor starch digestibility. The fat corrected milk (FCM) yield also decreased as DM content increased; FCM yield was lowest for VHDM (68 versus 74 pounds per cow per day on average).
It was also observed that kernel processing increased starch digestibility when LOC was .93 to 2.86 cm. (.36 to 1.1 inches). Even though kernel processing of corn silage can improve starch digestibility across a wide range of DM contents and LOC, kernel processing does not overcome the adverse effects of lower starch digestibility when DM content is higher.
The key to making good corn silage is first and foremost dependent upon the proper moisture level of about 68 to 72 percent. This range of moisture enables the fermentation process to progress quickly, allowing for the optimal production of lactic acid which stabilizes and preserves the organic matter. The quick removal of air from a pile or a silo halts the oxidation and heating that can damage the fiber and starch. Harvesting practices have a profound impact on the quality of corn silage and, consequently, the milk production it can elicit.
Another practice that's quite common in the Northeast is the delivery of small quantities of corn silage taken from a larger, established pile to a dairy farm. Smaller dairy farms that do not grow their own corn do this for economic reasons. However, corn silage, once disturbed, begins to immediately "re-cook" due to the addition of oxygen to the moist organic matter. Another paper, published by the ARPAS this past April, examined the value of topdressing an inoculant on piles of corn silage that had been relocated.2
As would be expected, yeast counts in the control silage pile (no inoculant) began to increase quickly and mold counts were very high after 330 hours. However, the researchers determined that corn silage topdressed with a silage inoculant could only be stored under cover for five days before it too began to suffer appreciable spoilage. The study appears to suggest that, regardless if a pile is topdressed or not or not with an inoculant, silage that's relocated and stored at a different location should be fed out in a week's time.
The study, which was conducted during the winter in a northern climate, also concluded that even though yeasts and molds proliferate rapidly, dry matter, fiber, protein and fermentation acid levels were unaffected by the relocation of a treated pile. The minerals calcium, phosphorus, potassium and magnesium remained the same and mycotoxins did not increase. Unfortunately, this study did not examine whether milk production was affected by the feeding of corn silage that had been relocated.
The continuing escalation of purchased feed prices for dairy diets has increased the necessity for dairy farms to focus on forage quality. As we approach another corn harvest, it's becoming more critical that dairy farmers and crop farmers concentrate on producing and managing their corn silage so as to minimize organic losses, poor fermentation and spoilage, and look to their corn silage as a superior source of digestible fiber and energy for dairy herds.
1Meta-Analysis: Effect of corn silage harvest practices on intake, digestion and milk production by dairy cows; L. F. Ferraretto and R. D. Shaver, PAS, Department of Dairy Science, University of Wisconsin - Madison
2Case Study: Adding a bacterial inoculant to corn silage removed from a bunker silo and stored in piles; P. S. Erickson, N. L. Whitehouse and D. A. Spangler, Department of Biological Sciences, University of New Hampshire, and Agri-King, Inc.
The author is a dairy nutritional consultant and works for Central Connecticut Farmer's Cooperative in Manchester, Conn.