Proceedings of the 3nd Mid-Atlantic Nutrition Conference. 2005. Zimmermann, N.G., ed., University of
Maryland, College Park, MD 20742.
USING PARTICLE SIZE MEASUREMENTS
FOR FEEDING MANAGEMENT OF
CORN SILAGE BASED DAIRY RATIONS
A.J. Heinrichs P.J. Kononoff G.I. Zanton
Dept. of Dairy and Animal Sci. Dept. of Animal Science Dept. of Dairy and Animal Sci.
Penn State University University of Nebraska Penn State University
324 Henning Building C220 Animal Science 324 Henning Building
University Park, PA 16802 Lincoln, NE, 68583-0908 University Park, PA 16802
Phone: 814-863-3916 Phone: 402-472-7442 Phone: 814-863-4199
Fax: 814-863-3916 Fax: 402-472-6364 Fax: 814-865-7442
Email: ajh@psu.edu Email: pkononoff2@unl.edu Email: gzanton@psu.edu
Summary
Particle size analysis has become a routine technique used in forage and total mix rations (TMR)
evaluation. The objective of this paper is to review background information related to diet particle size
and to describe how it may be used to further understand rumen fermentation and feeding behavior
with particular emphasis on corn silage-based rations. Monitoring particle size also can serve as a useful
tool to monitor sorting behavior of dairy cattle and can be used to troubleshoot a variety of feeding,
digestion, metabolic, and production related problems. Plotting the particle size distribution of both
TMR and refusals can provide valuable insight for evaluating the degree of sorting behavior exhibited by
dairy cows.
Introduction
Evaluating a ration to determine if it will meet the nutrient requirements of high producing dairy
cows requires detailed understanding of the chemical components of feeds, including protein, minerals,
and fiber, as well as some knowledge of the physical characteristics of the feeds being fed, including
particle size (Van Soest, 1994). All of these parameters can be used in ration formulation for dairy cows,
and both chemical and physical factors will impact rumen function and feedstuff digestion in high
producing dairy cows.
Greater recognition of the importance of forage particle size in dairy cow nutrition has arisen in
the past several years. It has become increasingly important to understand ration particle size as we
strive to formulate diets that will allow dairy cows to reach their genetic capability in terms of milk
production (Heinrichs et al., 1999). As we raise milk production we raise the total nutrient needs of the
animal, making it more important that we maintain peak levels of dry matter and energy intake while
keeping the rumen environment in a stable and consistent state. In addition, forage components of the
ration have increasingly become silage-based in the Northeastern United States because it is a cost
effective nutrient source for dairy cattle. This again imparts greater importance to silage particle size in
relation to the total diet of the lactating dairy cow.
TMR Particle Size and Rumen pH
Nutritionists are often concerned about rumen pH because when pH levels fall below 6.0 fiber
digestion will likely be reduced (Russell and Wilson, 1996). Generally speaking, rumen pH is a function
of volatile fatty acid (VFA) production and utilization, lactic acid in particular; and rumen pH is buffered
by saliva (Maekawa et al., 2002). Due to this understanding of rumen pH regulation, it is common
practice to feed diets of longer particle size and greater amounts of effective fiber so that saliva
production is stimulated. In support of this fiber and pH relationship, Krause et al. (2002) noted that
intake of particles > 19.0 mm was negatively correlated to the amount of time rumen pH spent below
5.8.
However, we also know forage should not be harvested at excessively long lengths. Kononoff and
Heinrichs (2003a) demonstrated that if diet particle length is too long eating patterns may be affected
and may result in lower mean rumen pH, even though chewing activity may be increased. In this study,
increasing the proportion of particles > 19.0 mm from 3 to 12% of the diet did not result in increased
chewing activity or effect rumen pH. However, further increasing the proportion of long TMR particles
to 31% resulted in depression of mean rumen pH, which was thought to be a result of changes in eating
behavior, reduced intake of total diet neutral detergent fiber (NDF), and increased sorting tendencies.
In light of these studies, it is apparent that particle size may affect rumen pH but differences in
particle size do not always result in differences in mean rumen pH. When evaluating a diet to determine
a possible risk of subclinical acidosis, we should review levels of fiber and non-structural carbohydrates,
along with their associated fermentability (Yang et al., 2001a). Practically nutritionists should be
foremost ensure that the chemical composition of the diet meets NRC recommendations and then
subsequently review the physical composition of the diet which may also have effect on rumen
fermentation.
Particle Size Recommendations for Corn Silage and Corn Silage Rations
Although no recommendation may apply adequately to all feeding systems, Table 1 outlines
forage and TMR particle size recommendations according to Penn State researchers, DAS 02-42
(Heinrichs and Kononoff, 2002). The chop length of corn silage must allow for proper good packing and
subsequent fermentation. Proper packing and a desirable fermentation will also aid in removing silage
while maintaining its quality at high levels, which will result in better overall forage quality (Jones et al.,
2004). The listed corn silage particle size recommendations aim to have the majority of forage particles
fall within the two middle screens of the Penn State Particle Separator (PSPS). For the top sieve, a
maximum of 3 to 8 percent is preferred. This top portion is one of the two fractions that will provide
particles to be ruminated; however these largest particles are also easy for a cow to sort. We need to
strive to limit sorting behavior and therefore need to limit the amount in this top screen. This means 45
to 65 percent of the silage material should remain on the middle sieve and 30 to 40 percent on the
lower sieve of the separator. No more than 5 percent should be recovered in the bottom pan. As corn
silage makes up a greater proportion of the ration, more material should remain in the middle two
sieves and less in the top sieve and bottom pan. The second layer of the PSPS is very important as the
corn silage material on this screen is as important for good rumen function as the material on the top
screen, yet this material is not “sortable” by the cow. Therefore, in many cases the forage on the second
sieve is even more critical than the top sieve for maintaining good rumen function.
Note that particle size recommendations are not related to the type of harvesting equipment. It is
the end product, not how it got there, that is important. Newer systems for harvesting corn silage
(chopping and rolling in one process) can create silage with a large percentage of long forage particles
without large pieces of whole cobs or stalks, the vast majority falling into the center two layers of the
PSPS. This forage can be excellent quality because it packs and ferments well in the silo and does not
allow for a “sortable” ration. Typically, when conventional choppers are set to harvest corn silage at a
long particle size, forage is predisposed to poor silo compaction and mold formation. The material
usually has large pieces of cob, dry stalks, and leaves that allow a great deal of sorting and often may be
refused by high producing cows. No matter what type of harvesting equipment that is used, the silage
particle size recommendations are the same.
Table 1. Forage and TMR particle size recommendations as estimated by the Penn State
Particle Separator.
a As estimated by the Penn State Particle Separator (Kononoff et al., 2003a).
b MPL = geometric mean length as calculated by the ASAE (2001).
The recommended amount of material between 8.0 and 19.0 mm reflects the variation commonly
observed on commercial dairy farms (Heinrichs et al., 1999). As a result of the PSPS modification,
particle size recommendations for material < 8.0 mm is now further partitioned into the proportion
between 1.18 and 8.0 mm and the proportion < 1.18 mm. Given that no severely negative effects have
been observed in animals consuming rations that contained 30 to 50% of the ration particles between
1.18 and 8.0 mm in length, our recommendations are limited to that range (Kononoff and Heinrichs,
2003 a,b).
Few published studies have included the new sieve in particle size measurements; however, it is
generally understood that particles retained on a 1.18-mm sieve pass out of the rumen more slowly
than those not retained (Poppi et al., 1985). Recently, using a different method of dry sieving, Yang et
al. (2001b) demonstrated that the rumen outflow rate of particles less than 1.18 mm averaged 5.57%
per h compared to those retained on a 3.35-mm sieve, which had an average outflow rate of 1.75% per
h. Thus, the additional sieve should prove useful in further understanding of factors affecting rate of
passage.
Although the proportion of material < 1.18 mm was not different within two published experiments, no
negative effects were observed when as much as 20% of the material was less than 1.18 mm (Kononoff
and Heinrichs, 2003 a,b). We are thus are currently limited to recommend that TMRs contain no more
than 20% of the material < 1.18 mm. This recommendation may require further refinement based on
the relative amounts of soluble and degradable carbohydrate components in the TMR.
Understanding Sorting Using the PSPS Dairy rations must be balanced for proper nutrient intake in total
and result in constant feeding activity during the day. Because of a great many different feedstuffs, their
various physical and 3-dimensional properties, as well as their dry matter content variability, there are
no exact ration
specifications for total particle size range and distribution. Given a ration, which appears to be adequate
in terms of its chemical composition, particle size analysis can aid in our understanding of how nutrients
contained in the ration will be consumed by the animal.
A number of studies have been conducted that seek to improve our practical understanding of the
effects of forage particle size on the related features of daily feeding activity and behavior (Ebling and
Kung, 2004, Kononoff et al., 2003b). A recent experiment illustrated the effects of corn silage particle
size on the concentration of NDF remaining in the feedbunk over a 24-h period (Kononoff et al., 2003b).
In this study diets were similar in NDF content but contained increasing amounts of material > 19.0 mm
in length (Table 2). Animals consuming the diet of longest particle size refused more fiber particles, as
demonstrated by the highest NDF content in the refusals (Table 3). Although reduction in chop length or
particle size is one method that may reduce sorting activity, mechanical processing of corn silage has
also
been observed to be effective. In a study designed to evaluate the effects of feeding either processed
orunprocessed corn silage, Ebling and Kung (2004) noted a high degree of sorting 18 and 24 hours after
feeding unprocessed silage. Although no deleterious effects were observed in feeding unprocessed corn
silage, this was likely due to the relatively fine TMR fed (i.e. less than 10% was > 19.0 mm). It should be
noted that even if TMRs contain unprocessed corn silage, extensive sorting activity is usually not
observed if the particle size is close to recommended ranges listed in Table 1. Thus, although finely
chopping or processing corn silage increases the power requirements and harvesting costs, studies
demonstrate that these practices also reduces the sorting behavior of dairy cattle.
Table 2. Particle size measurements of refusals for animals fed one short and one long corn
silage-based TMR (Kononoff et al., 2003b).
Table 3. The effect of feeding two rations of different particle size on the NDF
concentration of refusals (Kononoff et al., 2003b).
Some of the typical reasons that cows sort their TMR diets are because they: contain a general
long particle size, are very dry (>60% dry matter), have great variation in density of ingredients, or
contain a large amount of dry hay. In each of these cases, the physical attributes of the TMR allow it to
be easily separated by the cow. Other feed system attributes that cause increased sorting are related to
feed bunk space per cow, amount of time that feed is available, and bunk management, which is related
to the number of times that a TMR is fed per day along with the number of times that the TMR and feed
is pushed up to the cows.
Cows typically sort against large particles, especially if the longer forage particles are feedstuffs
that have stems. Typically, dry alfalfa hay is easy for dairy cows to sort; however coarse grass hay and
coarsely chopped corn silage also can be sorted. Research has shown that high producing cows have the
greatest ability to sort feed compared to other groups of cows in the herd. Feed sorting should be
avoided
if at all possible. The effects on dairy cattle are never good, as production and herd health suffer when
cows sort. Therefore, it is advisable to evaluate your feeding system in relation to any sorting problems
and to use good feed management practices that avoid sorting. Some ways to reduce sorting include:
feed
more frequently and push feed up often; use high quality hay and process it properly before putting it in
the TMR; process corn silage if it is dry; be sure that the forage chopper is functioning properly and
knives are sharp to avoid long pieces of corn silage stalks, leaves, and cobs; use fibrous byproduct feeds
so that the finer portion of the TMR is higher fiber; be sure that no forage component is longer than
4inches; and avoid feeding to an empty bunk. Also keep in mind that anything that promotes
competition
at the feed bunk makes sorting and consumption of large concentrate meals possible.
There are no recommendations that apply to all feeding systems and feed types. Aspects such as
number of times fed per day, forage type, fiber level, grain composition, and so on, all affect the
recommended particle size for the diet. Particle size evaluation of TMRs and refusals is an important
component of feeding high producing dairy cows. Because sorting activity can result in fluctuations of
rumen fermentation, TMR diets need to be formulated to ensure that fiber particles are long enough to
stimulate chewing activity but not so excessively long that they encourage sorting behavior.
References
ASAE. 2001. S424. Method of determining and expressing particle size of chopped forage materials by
sieving. In Standards. Am. Soc. Agric. Eng., St. Joseph, MI.
Ebling, T.L. and L. Kung, Jr. 2004. A comparison of processed conventional corn silage to unprocessed
and processed brown midrib corn silage on intake, digestion, and milk production by dairy cows. J.
Dairy Sci. 87:2519-2527.
Heinrichs, A.J., D.R. Buckmaster, and B.P. Lammers. 1999. Processing, mixing, and particle size
reduction of forages for dairy cattle. J. Anim. Sci. 77:180-186.
Heinrichs, A.J. and P.J Kononoff. 2002. Evaluating particle size of forages and TMRs using the new Penn
State Forage Particle Separator. Technical Bulletin of The Pennsylvania State University, College of
Agricultural Sciences, Cooperative Extension. DAS 02-42.
Jones, C. M., A. J. Heinrichs, G. W. Roth, and V. A. Ishler. 2004. From Harvest to Feed: Understanding
silage management. Penn State University. Special Circular UD016.
Kononoff, P.J, A.J. Heinrichs, and D.R. Buckmaster. 2003a. Modification of the Penn State Forage and
Total Mixed Ration Particle Separator and effects of moisture content on its measurements. J. Dairy
Sci. 86:1858-1863.
Kononoff, P.J, A.J. Heinrichs and H.A. Lehman. 2003b. The effects of corn silage particle size on eating
behavior, chewing activities, and rumen fermentation in lactating cows. J. Dairy Sci. 86:3343-3353.
Kononoff, P.J. and A.J. Heinrichs. 2003. The effect of decreasing corn silage particle size and the
inclusion of cottonseed hulls on effective fiber values and ruminal fermentation. J. Dairy Sci. 86:33433353.
Kononoff, P.J. and A.J. Heinrichs. 2003a. The effect of decreasing alfalfa haylage particle size on
effective fiber values and ruminal fermentation. J. Dairy Sci. 86:1445-1457.
Krause, K.M., D.K. Combs, and K.A. Beauchemin. 2002. Effects of forage particle size and grain
fermentability in midlactation cows. II. Ruminal pH and chewing activity. J. Dairy Sci. 85:1947-1957.
Maekawa, M., K.A. Beauchemin, and D.A. Christensen. 2002. Effect of concentrate level and feeding
management on chewing activities, saliva production, and ruminal pH of lactating dairy cows. J. Dairy
Sci. 85:1165-1175.
Poppi, D.P., R.E. Hendrickson, and D.J. Minson. 1985. The relative resistance to escape of leaf and stem
particles from the rumen of cattle. J. Agric. Sci. 105:9-14.
Russell, J.B. and D.B. Wilson. 1996. Why are ruminal cellulolytic bacteria unable to digest cellulose at
low pH? J. Dairy Sci. 79:1503-1509.
Van Soest, P.J. 1994. Nutritional Ecology of the Ruminant, 2nd
ed. Comstock Publishing Associated, a
division of Cornell University Press.
Yang, W.Z., K.A. Beauchemin, and L.A. Rode. 2001a. Effects of grain processing, forage to concentrate
ratio, and forage particle size on rumen pH and digestion by dairy cattle. J. Dairy Sci. 84:2203-2216.
Yang, W.Z., K.A. Beauchemin, and L.A. Rode. 2001b. Barley processing, forage:concentrate ratio, and
forage particle size on chewing and digesta passage in lactating cows. J. Dairy Sci. 84:2709-2720.