Corn Silage as a Companion Forage: Pros and Cons

Transcription

1 Corn Silage as a Companion Forage: Pros and Cons Larry D. Satter U.S. Dairy Forage Research Center, USDA-Agricultural Research Service and Dairy Science Department, University of Wisconsin, 1925 Linden Drive West, Madison, WI lsatter@dfrc.wisc.edu Take Home Messages 8 There appear to be small advantages in terms of milk production with high producing cows when a blend of alfalfa and corn silage is fed. 8 Better whole-farm nutrient management is possible with a blend of alfalfa and corn silage. 8 There appear to be varietal differences between hybrids and their nutritional value, but this area is poorly understood. 8 Brown midrib 3, a mutant variety that contains less lignin, is of high nutritive value but has lower yield and has potential for stalk breakage. 8 Processing or roller milling of corn silage has a small benefit in terms of milk production, but has potential for significant economic impact. Introduction Despite very large differences in protein and starch content, alfalfa and corn silage can be substituted one for the other in dairy diets without much effect on milk production (Broderick, 1985; Colenbrander et al, 1986; Dhiman and Satter, 1994). This assumes, of course, that nutrients are balanced in the diet. This approximate equivalence (from the cow s point of view) is a tremendous advantage, for it opens up opportunities to exploit advantages that one crop may have over the other in certain situations. We can tilt the forage mix for a dairy operation to take advantage of the circumstances unique to that operation. The objective of this paper is to explore a role for corn silage in dairy diets where grass, legume and small grain forages have traditionally dominated. Advances in Dairy Technology (2000) Volume 12, page 369

2 370 Satter Performance Of Cows Fed Diets Differing In Proportion Of Forage Provided By Alfalfa And Corn Silage. Corn silage and alfalfa hay or silage are the two most important forages in North American dairy diets. They are complimentary feedstuffs in that alfalfa is high in protein and corn silage is low. They are complimentary crops in that the nitrogen-fixing legume is an ideal crop in rotation with corn. Corn silage can yield more biomass per acre and typically at lower cost per ton of dry matter than alfalfa. On the other hand, producing corn silage presents greater environmental risk, even more than growing corn for grain, because virtually no crop residue remains following harvest. Identifying the optimum blend of these two forages for a given dairy operation (where both forages can be produced) is a systems question, taking into account soil quality, nutrient management, labor supply, feed storage, cow response, etc. Studies in the 1980 s with cows that today we may consider as low or moderate in milk production level (25-30 kg/day) showed little difference in milk production as the proportion of alfalfa or corn silage in the diet was varied. Broderick (1985) found comparable milk production among cows fed diets based on ether high quality alfalfa silage or corn silage balanced with corn grain, soybean meal and other supplements. Colenbrander et al (1986) formulated diets that were based on equivalent concentrations of NDF using three combinations of alfalfa and corn silage and found no differences in actual milk production or milk composition. A complete lactation study with higher producing cows was conducted more recently (Dhiman and Satter, 1997). The experiment started at calving, and lasted until cows completed 44 weeks of lactation. Forty-five mature and 29 first lactation cows were randomly assigned before calving to one of three forage treatments according to calving date. The three treatments were: AS (alfalfa silage supplied all of the forage), 2/3 AS (alfalfa silage supplied 2/3 of the forage), and 1/3 AS (alfalfa silage supplied 1/3 of the forage). Corn silage provided the remainder of forage. The cows were fed diets containing 50% forage and 50% concentrate. Table 1 contains results for the entire lactation. Dry matter intakes were similar, but slightly higher for the 2/3 alfalfa treatment. Milk yields followed a similar trend, being slightly higher for the 2/3 alfalfa treatment. The mixed forage diets appeared to have an advantage in terms of milk fat and milk protein. No differences were noted in body weight change during lactation due to treatment.

3 Corn Silage as a Companion Forage 371 Table 1. Nutrient intake and lactation performance of primiparous and multiparous cows fed diets containing different proportions of alfalfa silage (AS) and corn silage (CS). 1 Diets 2 Measurement AS 2/3 AS 1/3 AS SEM Cows, no Dry matter intake, kg/d Milk yield, kg/d % FCM, kg/d Feed efficiency, kg FCM/kg of DMI Milk fat, % Milk protein, % d Milk yield, 3 kg Primiparous cows Multiparous cows ,170 10, Data summarized from wk 1 through 36 of lactation. 2 Diets contained a 50:50 forage to grain ratio. The forage portion of the diet consisted of AS, twothirds AS and one-third CS (2/3 AS), or one-third AS and two-thirds CS (1/3 AS). 3 Calculated by projecting milk yield for cows that were dried off before wk 44 of lactation. Using prices typical of early 1997, the cost (US$) of feed required per 100 kg milk for primiparous and multiparous cows fed the AS, 2/3 AS or 1/3 As were: $7.98 and 8.47; 7.67 and 7.63; 7.92 and Under current conditions, addition of corn silage to an alfalfa based forage program usually lowers the cost of milk production in many parts of the U.S. Less total protein was fed when the diets contained corn silage, but more supplemental protein was required. Feeding a blend of low protein corn silage with the high but easily degraded alfalfa protein enabled more efficient utilization of protein in the rumen. This resulted in less nitrogen excretion per unit of milk produced when the forage mixture was used. Borton et al. (1997) utilized a dairy forage system model (DAFOSYM) to compare the relative merits of alfalfa and corn silage when none, one-third, two-thirds or all of the forage requirement was met by ammoniated corn silage, and the remainder was alfalfa. DAFOSYM simulates the growth, harvest, storage and use of alfalfa and corn along with manure production, collection, storage and application to cropland on representative dairy farms over many years of varying weather conditions. Their simulation exercise indicated the highest net return was from alfalfa at 100% of the forage requirement, but differences in net returns across forage systems were small. Changes in assumptions concerning farm size, soil type, crop yield, milk production, relative prices, and manure handling did not affect the conclusions of the analysis. In

4 372 Satter systems that used all alfalfa forage, much of the manure was applied to alfalfa crops, a practice that is normally discouraged because the manure reduces weed control and stand persistence, and possibly forage quality. With alfalfa at 100% of the forage requirement, large amounts of excess nitrogen were present on the farm. They concluded that in the absence of having a strong economic advantage among the forage systems, the practice of having at least one-third of the forage as corn silage and one-third as alfalfa is favored to improve management of crops, manure disposal, and labor. The ability to obtain satisfactory yields of corn silage will be the overwhelming determinant of whether corn silage should be used on a dairy farm. The corn belt keeps expanding as new and better-adapted corn varieties become available. Impressive gains in corn silage yields have tended to make corn silage increasingly competitive with other forages. There are some distinct disadvantages in growing/feeding only alfalfa, or only corn silage as a dairy forage. In many parts of the U.S. where both alfalfa and corn silage can be grown, blends of the two forages are most popular. Effect of Corn Variety on Silage Quality Until recently, little attention has been given to the effect of hybrid variety on feeding value of the resulting silage. In the U.S. only about 10% of the corn is harvested as silage, and only half of that is planted with the intention of harvesting as silage. Seed companies in the past have viewed this as too small a market to warrant development of silage varieties. The growing use of corn silage in Northern Europe, and the vast potential in Eastern Europe for corn silage, is serving to stimulate interest in developing hybrids specifically for use as silage. The hybrids available today have been largely selected on the basis of grain yield. From a silage quality point of view, this is generally good, because the grain portion of the corn plant is the most digestible part of the plant (See Table 2). The question is whether we can develop hybrids that have a high grain yield along with enhanced digestibility of the vegetative part of the plant.

5 Corn Silage as a Companion Forage 373 Table 2. Dry matter, plant composition and in vitro digestibility averaged over three corn hybrids (Kuehn et al., 1999). In vitro Dry % of Crude Digestible Plant fraction Matter Dry Plant Protein NDF ADF Dry Matter % Husk, shank and silk Stalk, shank and tassel Leaves Cob Grain Silage Hunt et al. (1993) compared two corn hybrids (Pioneer 3377 and 3389) having similar total plant and grain yield to determine potential differences in nutritive value of the whole plant stover. Whole plant samples of 3377 had a lower percentage of NDF (42.7 vs. 48.1), ADF (26.3 VS. 30.0), and lignin (3.4 vs. 3.8). In vitro dry matter digestibility of whole-plant and stover samples were greater for 3377 than for Lower fiber content and greater digestibility for 3377 was not due to greater grain content; 3377 actually had slightly lower grain as a percentage of whole plant than 3389 (41 vs. 44%). In a growth trial, steers fed the 3377 silage diet had greater daily gain (1.09 vs kg/d) and had improved feed efficiency (6.75 vs feed:gain). Results of these and other studies (Allen, 1992) indicate that large differences in feed value of corn silage may exist among hybrids with similar grain content. There are many specialty corn hybrids being marketed for corn silage, and one that has received considerable attention is brown midrib (bm3). This corn has had a natural mutation involving a gene responsible for one of the enzymes involved in lignin synthesis. The effect is that bm3 consistently has less lignin, and consequently the vegetative part of the plant is more digestible. The lactation results with bm3 have been mixed. Perhaps the most promising results have been obtained by Oba and Allen (1999). They used 32 multiparous Holsteins in a simple switch-back experiment. In the first 4 week period, 16 cows each were fed either bm3 or control corn silage. In the second 4 week period, the treatments were switched. The ingredients (% of DM) in the diets were; corn silage, 44.6; alfalfa silage, 11.2; dry ground corn, 5.6; high moisture corn, 9.1; soybean meal, 19.0; cottonseed, 5.6; and vitamin and mineral mix, 5.0. Results of the experiment are in Table 3. The response to bm3 is quite dramatic in this experiment, with dry matter intake increasing 2.1 kg/day, and milk production increasing 2.8 kg/day. Figure 1 shows that the high producing cows responded to the bm3 silage to a greater extent than lower producing cows. Other experiments have not shown such a large milk production

6 374 Satter response to bm3, but milk production levels were lower in these experiments, and perhaps the cows simply were not in a position to respond to the higher quality bm3 corn silage. Table 3. Performance of cows fed either brown midrib 3 or control corn silage (Oba and Allen, 1999). Treatment bm3 Control P Dry matter intake, kg/d < Milk yield, kg/d < Milk fat, kg/d < Milk protein, kg/d < Body weight change, kg/d Figure 1. Relationship between mean milk yield over 14 d prior to the beginning of the experiment and the response of milk yield to the brown midrib 3 (bm3) treatment. Milk yield response (bm3 control) = x pretrial milk yield (r = 0.17; P < 0.03).

7 Corn Silage as a Companion Forage 375 There are agronomic disadvantages with bm3, because it yields approximately 10-15% less than many hybrids and the seed is considerably more expensive. It is also quite susceptible to stalk breakage. With less lignin, the stalks are weaker, and under conditions of strong wind or heavy corn borer infestation, stalk breakage could be a serious problem. It also dries down more slowly, so it could present problems under marginal growing conditions. While there is interest in bm3 for high producing cows, it is not a wise choice for everyone. It is encouraging, however, in that bm3 provides the best evidence that there is good potential for improving the nutritional value of existing corn hybrids. There are other specialty hybrids that are being promoted as silage varieties. These include high oil, waxy, and high lysine corn. The high oil hybrids have a larger seed germ, and it is the germ that contains oil. Normal corn grain contains about 3.5% oil, and high oil corn contains % oil in the kernel. The trials with high oil corn silages are inconclusive. There is likely to be a yield drag of about 5% with the high oil corn, and that combined with the higher cost of seed raises questions about whether it is profitable for silage production. Waxy corn has a higher proportion of branched chain starch than conventional corn (100% amylopectin vs. 75% amylopection for normal dent corn). A number of studies have shown slightly higher digestibility of the kernel for waxy corn compared to normal dent corn. The advantage is very small, however, and is difficult to measure. The waxy gene can be incorporated into regular hybrids, and if the cost of seed is no greater, it might be a good option. High lysine corn has been around for a long time, but many of the high lysine varieties have had reduced yields. While improvements have been made in yield potential, high lysine corn has had very limited use as a silage corn. Improving the nutritional value of corn silage through plant breeding is a slow, long term approach. Simply cutting corn silage at a greater height is a simple and effective way of improving quality. The lower part of the stalk has the lowest quality feed. Cutting at 50 cm rather than 20 cm can noticeably improve quality but will reduce yield by 5-7%. Surprisingly, there is little information with high producing cows on the potential benefit of this practice. There is considerable uncertainty over the amount of genetic difference in nutritional quality of corn silage varieties. Until recently, this area of inquiry has been largely ignored. This topic is receiving a lot more attention now, and there is reason to be optimistic about future progress in this area. The question of corn silage quality becomes more important as milk production continues to climb.

8 376 Satter Optimum Maturity For Harvesting Corn Silage The traditional recommendation has been to wait until the corn plant is physiologically mature before harvesting it for either grain or corn silage. Physiological maturity is reached when all of the nutrients have been translocated from plant tissue to the grain, and this coincides with appearance of the black layer visible at the kernel tip. This recommendation is still sound when applied to grain harvest, but it results in kernels that are normally too hard and dry when harvested as silage. Since so many kernels are either intact, or only slightly damaged after passing through the forage harvester, digestibility of these large grain pieces is reduced when they become too dry. It is not necessary to have complete translocation or movement of sugars from leaves to the kernels when the whole plant is harvested and fed. The cow will consume the sugars in either case. This of course is not true if only the grain is harvested. The recommendation for optimum harvest time therefore has changed from appearance of black layer to when the milk line is between 25-75% in its advance to the kernel tip. Starch digestibility will be significantly reduced in overly mature corn silage. The importance of timely harvest of corn silage is illustrated in Figure 2. Milk yield was greatest when corn silage was harvested at 1/2 2/3 milk line. When corn silage was harvested at 1/4 milk line, or at black layer, milk production was reduced (Bal et al., 1997; Harrison et al., 1996). Grain development is incomplete when corn silage is harvested too early, thus reducing the nutritive value of the silage. Harvesting at black layer results in overly dry kernels as well as reduced digestibility of the vegetative portion of the corn plant, since leaf and stalk tissue also decreases with advancing maturity. Using the milk line as a guide for when to harvest is very helpful, but it should not be relied on totally. It is important to measure moisture content of the total plant, having 32-38% dry matter as a goal. It is more important to harvest corn silage at the correct moisture content than at a particular milk line stage.

9 Corn Silage as a Companion Forage 377 % Maximal Milk Yield UW WSU Milk Line Development Figure 2. Effect of maturity of corn silage on milk production (Harrison et al., 1996; Bal et al., 1997). Processing Corn Silage Corn silage that has been passed through a roller mill is referred to as processed corn silage, and the roller mills are sometimes called kernelcrackers. While use of processed corn silage is relatively recent in North America, it has been used extensively in Northern Europe for more than a decade. European corn hybrids used for silage have more flint corn in their genetic background, leading quite possibly to a harder kernel that is more resistant to digestion, and potentially responsive to kernel cracking. Another important reason why processing of corn silage is more widespread in Europe is that a high proportion of the corn silage is harvested by custom operators with large forage choppers. The added expense of incorporating a roller mill into a forage harvester is much easier to justify if the cost is spread over a large volume of corn silage. Meanwhile, there have been developments in North America that have fueled interest in roller milling of corn silage. Corn breeders have been giving emphasis to more rapid dry down of the grain, resulting in a dryer and harder kernel at the time of corn harvest. Corn geneticists have also been responding to the interests of people marketing corn. Grain handlers want a hard, strong kernel that resists breakage during handling while en route to the customer. Some of the qualities desired in corn grain from a production or marketing point of view may in fact compromise the feeding value of the corn kernel. Another

10 378 Satter development stimulating interest in processing of corn silage is the increase in size of dairy and beef operations. More use of hired or custom harvest equipment, larger farms, and availability of forage harvesters equipped with a roller mill have all played a role in the growing popularity of processed corn silage in North America. The need for high producing dairy cows to have sufficient long fiber in their diet has resulted in more producers chopping corn silage at a longer theoretical cut. This results in larger cob pieces and more whole kernels in the silage, and more corn in the manure. A longer cut combined with processing enables long fiber particles while ensuring complete kernel breakage. Cob pieces are also broken, resulting in little or no sorting of cobs in the feed bunk. Not all processed corn silage is properly processed. It is important to have adequate fiber length, and to have complete kernel breakage. How can that be achieved? The normal theoretical length of chop (without processing) is about 1 cm (3/8 inch). This needs to be lengthened if the silage will go through a roller mill, because in passing through the rollers forage particles will undergo reduction in size. Typically, particle size of processed corn silage chopped at about 2 cm (3/4 inch) theoretical length of cut will have about the same particle size as unprocessed silage cut at 3/8 inch. Cutting at lengths longer than 2.5 cm (one inch) is not recommended at the moment. There have been reports of excessive bearing wear on the roller mill due to large cob pieces causing some chatter in the roller mill and premature bearing failure. Cutting at 2 cm takes less power than cutting at 1 cm, and tends to compensate for the extra power required for operation of the roller mill. For the moment, cutting at 2 cm theoretical length of cut is recommended. This may be stretched to 2.5 cm, but there is not much information on silage of such long chop length. In addition to obtaining appropriate length of cut, proper setting of the roller mill is important. Typically the speed of the rolls is permanently set, with one roll running at about 15% higher rpm than the other. The gap between the rolls, however, is adjustable, and can range from less than 1 mm to 15 mm or more. (Note: One mm equals about 40 thousands of an inch). To obtain complete breakage of kernels, a 1-2 mm gap will be required. Too often equipment operators open up the gap to increase harvest capacity. This can result in incomplete kernel processing. Always check the processed silage for intact kernels. It is possible that kernel characteristics due to stage of maturity, or to hybrid difference, can influence kernel breakage, With some hybrids it may be okay to increase the gap between rolls, but only if all kernels are being broken. In any case, gaps of much more than 2 mm will likely result in suboptimal processing. The goal is to have complete kernel breakage. Milk production response to processing of corn silage has been mixed. Results from 15 trials are available, and it appears that the average milk production increase due to processing is kg milk per cow per day. Milk fat test averaged about.07 percentage units higher for the processed then the control

11 Corn Silage as a Companion Forage 379 corn silage. (Satter et al., 1999). Starch digestion is typically increased with processing by about 2-5 percentage units. This increase in starch digestion with processing has almost always been observed. To be sure, these are very modest responses, and it could be argued that they fall within the range of experimental variation. On the other hand, upon considering all the information, including starch digestion, it appears that processing of corn silage is having some beneficial effect, albeit small. The trials comparing processed with control corn silages had the benefit, generally speaking, of good quality corn silage. Overly mature or dry corn silages were generally absent from this group of studies. One might expect more benefit from processing when applied to corn silage having more mature or harder kernels. The responses cited should therefore be considered as minimal responses. Most of the studies with processed corn silage have been short term switchback studies where changes in body weight or body condition could be reliably measured. If starch digestion is increased with processing, then either an increase in milk production, feed efficiency or in body condition should be observed. The potential benefits from the latter two have not been given much opportunity to be measured in the trials conducted thus far. The economics of processing corn silage probably does not work out for dairy operations of less than 100 cows, unless corn silage harvest is custom hired. The small milk production response, and the initial cost of the roller mill (US$ 9,000-15,000) preclude recovery of the equipment cost. For larger dairy operations, and especially for custom operators, a strong case can be made for equipping the forage harvester with a roller mill. Under U.S. economic conditions, dairy producers could afford to pay up to US$2.40 per ton for processing of corn silage based upon a.25 kg/day increase in milk production with processed corn silage. Most custom operators are charging much less than this, with reports ranging from no additional charge to US$1.50 per ton for the processing part of the custom harvest. When processing corn silage, be mindful of the need to a) use a longer theoretical cut (~ 2 cm), and b) inspect the corn silage to make certain that all kernels of corn are being broken. Some corn silage gets run through rollers that are spaced too far apart, resulting in little or no breakage of kernels. Conclusions Corn silage is an excellent forage when fed in combination with alfalfa or grass forages. Only small increases in milk production might be anticipated from feeding a blend of legume/grass and corn silage, but there are other

12 380 Satter advantages that can be important. Higher profitability and better farm nutrient management are often possible when corn silage is included in the dairy diet. Corn silage should be considered, however, only if it can be reliably grown in the area. The advantages of including corn silage in dairy diets cannot overcome the disadvantage of poor or unreliable yields of corn varieties that are poorly adapted to the growing conditions. References Allen, M.S Hybrid differences in corn silage forage quality. Proceedings of Wisconsin Forage Council s 16 th Forage Production and Use Symposium. Jan , Wisconsin Dells, WI. Bal, M.A., J.G. Coors and R.D. Shaver Impact of the maturity of corn for use as silage in the diets of dairy cows on intake, digestion and milk production. J. Dairy Sci. 80:2497. Borton, L.R., C.A. Rotz, J.R. Black, M.S. Allen and J.W. Lloyd Alfalfa and corn silage systems compared on Michigan dairy farms. J. Dairy Sci. 80: Broderick, G.A Alfalfa silage or hay versus corn silage as the sole forage for lactating dairy cows. J. Dairy Sci. 68: Colenbrander, V.F., D.L. Hill and M.L. Eastridge Formulating dairy rations with neutral detergent fiber. 1. Effect of silage source. J. Dairy Sci. 69: Dhiman, T.R. and L.D. Satter Yield response of dairy cows fed different proportions of alfalfa silage and corn silage. J. Dairy Sci. 80: Harrison, J.H., L. Johnson, R. Riley, S. Xu, K. Loney, C.W. Hunt and D. Sapienza Effect of harvest maturity of whole plant corn silage on milk production and component yield, and passage of corn grain and starch into feces. J. Dairy Sci. 79(Suppl. 1):149 Hunt, C.W., W. Kezar, D.B. Hinman, J.J. Combs, J.A. Loesche and T. Moen Effects of hybrid and ensiling with and without a microbial inoculant on the nutritional characteristics of whole-plant corn. J. Anim. Sci. 71: Kuehn, C.S., J.G. Linn, D.G. Johnson, H.G. Jung, and M.I. Endres Effect of feeding silages from corn hybrids selected for leafiness or grain to lactating dairy cattle. J. Dairy Sci. 82: Oba, M. and M.S. Allen Effects of brown midrib 3 mutation in corn silage on dry matter intake and productivity of high yielding dairy cows. J. Dairy Sci. 82: Satter, L.D., Z. Wu, V.R. Moreira, M.A. Bal, and R.D. Shaver Processing corn silage, Proc. of the 24 th Annual Minnesota Forage Conf., Rochester, MN. Pp