A Survey of Dry-Rolled Corn Particle Size and Fecal Starch in U.S. Midwestern Feedlots
Authors: Erin Schwandt, Dan Thomson, Chris Reinhardt and Steve Bartle
Beef finishing diets are commonly formulated with processed grain as a primary energy source to support rapid weight gain and improved feed efficiency. Processing methods including steam flaking, grinding or dry-rolling are known to improve the site and extent of total tract starch digestibility compared to whole grain (Owens and Sonderlund, 2012). Dry-rolled corn processing is a common practice in the corn-belt region of the U.S. Historically, coarsely processed, or cracked processing, has been recommended to refrain from producing too many fines that could result in lower rumen pH and digestive disturbances. However, with distiller’s grains being included in finishing diets at higher levels in these regions as a cost effective ingredient to improve diet consistency and reduce sorting, overall starch concentration is reduced. There may be an opportunity to grind corn to a finer particle size to improve total tract starch utilization without causing reduced ruminal pH and digestive disturbances.
Research in the area of dry-rolled corn particle size recommendations for finishing cattle fed diets containing distiller’s grains is needed. This survey provides the industry with a baseline of current practices and an average particle size distribution from current dry-rolling practices. In addition, this survey reported average fecal starch content and by-product and roughage inclusion levels.
Materials and Methods:
Feedlots: Several consulting nutritionists participated in this survey by providing contacts to feedlots willing to participate (n = 34). Selected feedlots were from regions where feeding dry-rolled corn is a common practice and ranged in size from approximately 100 to 18,000 head. Feedlots were to use dry-rolled corn as a primary energy source, have cattle on a finishing diet for a minimum of 5 days, and to provide diet composition.
Data Collection: Data collection included a dry-rolled corn sample, fecal sample, diet sample and diet composition. Dry-rolled corn samples were collected from the ground-corn storage pile. Approximately ½ pound samples were collect across three to four locations of the pile about six inches from the surface. If corn was ground directly into the mixer truck (n = 2) the sample was collected in the mix truck while filling. Diet samples ½ lb were collected across five locations of the bunk immediately after feeding. Samples (n = 5 per pen) were collected in a 5 gallon bucket, hand-mixed, and poured out onto a clean surface. Pile was quartered, and two aliquots of diet were sub-sampled from two opposite quarters, placed in a plastic bag and frozen. Fecal samples were collected from nine fresh stools within each feedyard from cattle on a finishing diet, composited and frozen.
Data Analysis: Dry-rolled corn samples were analyzed at the Kansas State University Feed Technology Innovation Center (Manhattan, Kansas) for particle-size distribution using a Tyler Ro-Tap Sieve Shaker. Samples were mixed and a 100 gram subsample was weighed out. The sample was placed in the top sieve of the sieve stack and placed on the Ro-Tap for 10 minutes. and each sieve was weighed and recorded. Sample analysis was conducted in duplicates. Diet samples were analyzed at SDK Labs (Hutchinson, Kansas) for the following analysis: Moisture, dry matter, crude protein, ADF, NDF, NEL, NEG, NEM, TDN, DE, ME, fat, calcium, phosphorus, potassium, magnesium and RFV. Fecal samples were analyzed at SDK Labs (Hutchinson) for the following analysis: Moisture, dry matter, and total starch.
Two values are needed to describe particle size distribution, one is an estimate of the geometric mean diameter (Dgw), and the other is an estimate of the range of particle sizes in the sample, or the standard deviation of the geometric mean diameter (Sgw). Results are presented in Table 1. The overall Dgw of all feedlots averaged 4,201 microns and is approximately the corn kernel fractioned into thirds (Figure 1). The range for the Dgw was 1,165 to 6,823 microns and the Sgw averaged 1,864 microns.
Roughage inclusion level averaged 8.5 ± 1.8%; NDF levels averaged 19.2 ± 4.2% on a dry matter basis (Table 2).
Fecal starch content averaged 18.9 ± 6.5%; by-product inclusion level averaged 26.8 ± 13.7%, or stated another way, about 19% of the fecal material was starch. Given that some starch escapes digestion and ends up in the feces indicates there may be an opportunity to increase the degree of grain processing in some feedlot operations to improve total tract starch utilization. Data from this survey provides the industry with an average dry-rolled corn particle size for feedlots located in one region of the U.S. and should contribute to manufacturing considerations when feeding higher levels of by-products in the diet.
Literature Cited: Owens, F. and S. Sonderlund. 2007. Ruminal and postruminal starch digestion by cattle. http://beefextension.com/proceedings/cattle_grains06/06-17.pdf (Accessed 10 November 2013)