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Feeding Corn Silage Takes Considerations


Feeding Corn Silage Takes Considerations

In my travels, I spend a considerable amount of time looking at corn silage bunkers and discussing silage feeding concerns with dairy producers and their nutritionists.

Over the years, with the helpful input of some very capable nutritionists, I have developed a hierarchy of things I tend to focus on when evaluating herds feeding rations high in corn silage (e.g., 20-25 lb. of dry matter per cow).

SILAGE BUNKER: There are many factors to take into consideration when
feeding high-corn silage rations, starting with inspecting the source - the silage
bunker, like the one shown.

The Bunker Side

I prefer to start at the source and work my way to ration considerations. With safety in mind, I like to physically observe the bunker, looking at the face management as a general indicator of detail to forage feeding management. I look for signs of top and side spoilage and, if extensive, try to assess how spoiled feed is handled.

Consultants need to know if corn silage is being fed from more than one bunker or bag and how many different hybrids from different fields were packed in the same bunker. Additionally, it is helpful to determine how much dry matter, starch and neutral detergent fiber (NDF) variation is being modified by feeding off the entire face rather than feeding from small sections of the bunker (Stone, 2003).

Many nutritionists like to "bury their nose" in silage to assess the smell, but I don't recommend this for three reasons: (1) it is not a healthy practice to be inhaling mold spores often found in silage, (2) if there is an undesirable fermentation profile, this can be easily detected at a distance (and confirmed with volatile fatty acid analysis) and (3) in my opinion, smell is not a very good field indicator of either palatability or nutritional value.

I do like to look for any signs of heating in the silage. Seeing steam roll off a recently faced bunker during cold weather does not necessarily indicate aerobic instability problems. This is often just ambient harvest temperature and normal fermentation heat that is retained by water acting as a heat sink in the silage mass. A better indicator of microbial-induced heating is if the silage continues to heat up after it has been faced and is lying in a pile or in the feed bunk.

Kernel Damage

Perhaps the most overlooked aspect of assessing corn silage at the bunker is attention to physical damage of the corn kernels. I have developed my own bunker-side field method that I have subjectively calibrated against laboratory RoTap methods.

I scoop as much silage as I can in both hands from several locations across the face of the bunker. I then spread out the silage on the bunker floor and pick out any kernel pieces that are larger than a quarter-kernel. If the sample contains more than two or three of these kernel pieces, I try to convince the dairy to have a kernel processing test conducted to help in potentially discounting the energy value of the silage.

Looking at the kernels also helps me estimate the maturity of the corn at harvest. If kernels are more immature, then lower starch, slightly higher oil (the germ is not as diluted by starch) and higher sugar content would be expected on the forage analysis. This can influence both ration formulation and the tendency bunk life and palatability problems.

Feed Delivery

Monitoring particle size is very important in a high-corn silage ration. In addition to looking at corn silage chop length (ideally about 19 mm), I also like to note the chop length and texture of the other forages that are going into the total mixed ration (TMR) to get a feel for functional fiber levels in the ration.

If possible, I also watch the feeder load the TMR to observe both feed sequencing and length of time the corn silage has been exposed to mixing.

Particle size and nutritional analysis of the TMR at feed delivery are often helpful to detect mixer abuse of fiber particle size as well as to assess mixer consistency (Nelson, 2008).

The Cow Side

Cows are the ultimate judge, so before I look at rations, I like to observe cattle feeding behavior, cud chewing and appearance of the TMR in the feed bunk.

I am primarily interested in any evidence of ration sorting either by observing cows eating or by analyzing the push-out TMR. Other observations, such as access time to the feed bunk and incidence of cows lying down properly in stalls or lots, should also be correlated with production, components and milk urea nitrogen levels (Nelson, 2008).

Some herds feeding high-corn silage rations have resorted to incorporating straw or poor-quality hay in the mix to stimulate rumination. This approach often helps when forage particle size is not suitable. However, the downside is that these rations often have upwards of 20% on the top screen of a three-sieve Penn State separator and as much as 60% on the bottom pan.

High-corn silage rations containing suitable forage particle size, thus not requiring added straw or hay, provide a better particle distribution with as much as 60-65% of particles on the top two sieves (Drehmann, 2008).

Ration Formulation

Fiber. Nutritionists understand that they must balance for the amount of nutrients and not just percentages. For corn silage, we tend to focus on NDF content (highly related to the dilution effect of starch content) and also NDF digestibility (NDFD).

Nutritionists are beginning to understand that NDFD is only a guide and that even the best labs have about a two to three percentage point variation in estimates associated with these values. This is why monitoring absolute pounds of forage NDF intake and paying close attention to the condition of the manure is what continues to guide the ration adjustments of many field nutritionists.

Nutritionists feeding high-corn silage rations tend to feed slightly higher levels of NDF in the entire ration. A review by Linn (2003) indicated that 30% NDF in the ration can be fed in high-corn silage rations without loss of milk production.

In rations where physically effective NDF (peNDF) levels are tracked, most high-corn silage herds prefer balancing at 22-23%, which is at the high end of typical peNDF recommendations. Most nutritionists prefer a minimum of 12.0-12.5 lb. of NDF from forage in high-corn silage rations when cows are consuming 56 lb. of total dry matter per day. This works out to about 22% of the ration NDF coming from forages.

These fiber levels are often exceeded (24-25% total NDF from forages) if the corn silage is particularly high in NDFD due to either the effect of growing season (drought), hybrid genetics or the use of forage additives proven to improve NDFD (Drehmann, 2008; Nelson, 2007; Mahanna, 1999).

Some nutritionists monitor the relationship of forage NDF to the level of rumen fermentable starch (determined by calculation or estimated via in situ or in vitro lab methods). Providing 1.25 lb. of NDF for each 1 lb. of fermentable starch has proven to be a useful thumb rule, especially in rations containing very high NDFD corn silage (Nelson, 2008).

Starch. The starch in corn silage is often considered the "villain" when cows fed high levels of silage do not respond as expected, experience low butterfat tests or display inconsistency in manure scores. However, the villain image has lessened as laboratory starch values have become commonly available and nutritionists have learned to focus on reducing supplemental grain to complement the starch delivered in modern genetics and also factor in the effect that time in storage has on increasing ruminal starch availability (Mahanna, 2007).

Starch levels in the entire ration typically range from 24% to as high as 30% (somewhat lower when supplemental sugar sources are added to the ration). It is virtually impossible to exceed these total ration starch levels with corn silage, even under the highest inclusion rates of the high-starch corn silage.

Fat. A review of tallow supplementation (2% of the ration) in high-corn silage rations showed some tendency to reduce dry matter intake and lower test, although cause and effect were unknown because rumen parameters were not significantly altered (Linn, 2003).

It is likely that these problems can be avoided with our current understanding of the trans-fatty acid theory of butterfat depression along with the ability of ration software to track estimates of unsaturated (especially linoleic acid) intakes (Perfield and Bauman, 2005).

Protein. One area that has recently captured my interest is the protein supplementation of corn silage rations. Attention to both protein quantity and quality has helped with the implementation of high-corn silage rations in herds that had previously struggled under this type of forage feeding regime (Drehmann, 2008).

In the past, there may have been a tendency to provide excess rumen-degraded protein (RDP) from increased protein supplementation, which is justified when (lower-protein) corn silage replaced (higher-protein) alfalfa in the ration. Rations high in crude protein (CP) and RDP seem to complement high-corn silage rations by promoting high microbial protein yields (Linn, 2003).

However, having excess CP and RDP is a luxury that can no longer be tolerated as soybean meal prices elevate, nitrogen-related environmental concerns mount and more is learned about urea and intra-ruminal nitrogen recycling and the specific amino acid needs of high-producing cows. On the flip side, overfeeding rumen-undegraded protein can be expensive and decreases efficiency of ration metabolizable protein because it generally has lower concentrations of lysine and methionine than microbial protein (Varga, 2007).

Research from the U.S. Dairy Forage Research Center and the University of Illinois clearly showed that milk production was enhanced when ration CP levels were closer to 17% than either 15 or 19%, especially when a blend of plant/animal/marine protein supplements or rumen-protected methionine were included in the ration (Brito and Broderick, 2007; Broderick, 2007; Ipharraguerre et al., 2005).

Excessive CP also takes up space in the ration that could be filled with an energy source and can also result in a net energy burden to the animal from protein deamination to ammonia and conversion to urea for excretion (Broderick, 2007, NRC, 1989).

Another reason not to overfeed CP is that we may be underestimating cows' ability to recycle urea-nitrogen through saliva or through the rumen wall (Lapierre and Lobley, 2001). The current dairy nutrient requirements (National Research Council, 2001) do not account for nitrogen recycling, which likely contributed to an overestimation of RDP requirements.

RECENT studies from Cornell have shown that even sophisticated models like CPM v3 may be underestimating recycled urea nitrogen by 50-75% (Recktenwald and Van Amburgh, 2007).

Success was achieved in rations containing upwards of 25 lb. of dry matter from high-starch corn silage by targeting 16.0-17.5% CP levels with conservative levels (8.0-8.5% dry matter) of RDP (Drehmann, 2008).

The use of ration software that can track amino acid intake has allowed for a reduction in increasingly expensive CP sources like soybean meal. These ration savings can be effectively used to supplement more balanced amino acid blends of plant/animal/marine proteins or commercial rumen-protected methionine products.

The Bottom Line

Corn silage inclusion rates are on the rise due to availability of supply, energy density, consistency and palatability. Close attention should be paid to silage starch content and availability, NDF content and digestibility and physical attributes such as peNDF, kernel damage and feed storage/delivery management. High-corn silage-based rations should include moderate levels of CP and RDP with specific attention to lysine and methionine levels supplied from plant/animal/marine or rumen-protected sources.


Brito, A.F., and G.A. Broderick. 2007. Effects of different protein supplements on milk production and nutrient utilization in lactating dairy cows. J. Dairy Sci. 90:1816-1827.

Broderick, G.A. 2007. Reduced crude protein rations for high producing cows — Production and environmental effects. Proc. 69th Cornell Nutrition Conference for Feed Manufacturers. Oct. 23-25. Syracuse, N.Y.

Drehmann, P. 2008. Personal communication.

Ipharraguerre, I.R., and J.H. Clark. 2005. Varying protein and starch in the diet of dairy cows. II. Effects on performance and nitrogen utilization for milk production. J. Dairy Sci. 88:2556-2570.

Ipharraguerre, I.R., J.H. Clark and D.E. Freeman. 2005. Varying protein and starch in the diet of dairy cows. I. Effects on ruminal fermentation and intestinal supply of nutrients. J. Dairy Sci. 88:2537-2555.

Lapierre, H., and G.E. Lobley. 2001. Nitrogen recycling in the ruminant: A review. J. Dairy Sci. 84:E223-236.

Linn, J. 2003. Making high corn silage diets work. Proc. Minnesota Dairy Conf. & Dairy Expo. St. Cloud, Minn. p. 58-63. Accessed at

Mahanna, W.C. 1999. Dairy cow nutritional guidelines. In: Howard & Smith. Current Veterinary Therapy. 4th edition. W.B. Saunders Co.

Mahanna, W.C. 2007. Watch for changing starch digestibility. Feedstuffs. June 11. p. 12-13.

National Research Council. 1989. Nutrient Requirements of Dairy Cattle. 6th revised edition. National Academy Press, Washington, D.C.

National Research Council. 2001. Nutrient Requirements of Dairy Cattle. 7th revised edition. National Academy Press, Washington, D.C.

Nelson, A. 2008. Personal communication.

Perfield II, J.W., and D.E. Bauman. 2005. Current theories and recent advances in the biology of milk fat depression. Proc. 67th Cornell Nutrition Conference for Feed Manufacturers. Oct. 18-20. Syracuse, N.Y.

Recktenwald, E.B., and M.E. Van Amburgh. 2007. Examining nitrogen efficiencies in lactating dairy cattle using corn silage based diets. Proc. 69th Cornell Nutrition Conference for Feed Manufacturers. Oct. 23-25. Syracuse, N.Y.

Stone, W.C. 2003. Reducing the variation between formulated and consumed rations. Proc. 65th Cornell Nutrition Conference for Feed Manufacturers. Oct. 21-23. Syracuse, N.Y.

Varga, G.A. 2007. Why use metabolizable protein for ration balancing? Proc. Penn State Dairy Cattle Nutrition Workshop. Nov. 13-14. Grantville, Pa.

This article was originally published in February 2008 Feedstuffs issue, and is reproduced with their permission.