Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2012
Publication Date: 5/22/2012
Citation: Hoffman, P.C., Mertens, D.R., Larsen, J., Coblentz, W.K., Shaver, R.D. 2012. A query for effective mean particle size of dry and high moisture corns. Journal of Dairy Science. 95:3467-3477. Interpretive Summary: Dry and high-moisture corns are typically processed prior to feeding to enhance their nutritional value for lactating dairy cows. In practical terms, decreasing mean particle size (MPS) of dry or high-moisture corn increases surface area for rumen bacterial attachment, thereby increasing ruminal or total tract digestion. However, this relationship is complicated by the fermentation process for high moisture corns; at a similar MPS, the digestibility of high-moisture corn is usually greater than dry corn. The objective of this study was to investigate whether a concept of effective mean particle size, based on fermentation potential, was applicable for dry and high moisture corns. Throughout the experiment, peak absolute rate of in vitro gas production was used as a relative measure of fermentation potential. When on-farm methods were used to estimate MPS, dry corns required a smaller MPS than high-moisture corns to produce an equivalent peak absolute rate of gas production. Subsequently, some of this discrepancy was eliminated by using standardized laboratory methods to measure MPS. Further adjustment of MPS for dry and high-moisture corns using concentrations of prolamin and ammonia, respectively, created an estimate of effective MPS that essentially removed the bias between corn types. This information will allow nutritional consultants to better relate MPS with fermentation potential for dry and high-moisture corns, and then better utilize corn as a high-energy concentrate in the diets of lactating cows.
Technical Abstract: Eighteen dry and high moisture corns submitted to the University of Wisconsin Soil and Forage Analysis Laboratory (Marshfield, WI) for routine analysis were retained for mean particle size (MPS) and chemistry determinations. Mean particle size of corns was determined by the methods of the American Society of Agricultural Engineers (MPS-ASAE) or a simulated on-farm method (MPS-FARM). Corns were evaluated for DM, CP, soluble CP, NDF, starch, NH3-N, prolamin protein, and fat. In vitro gas production of undried, unground corns was evaluated, and peak absolute rate of gas production (mL/g DM/h), time of peak absolute rate (h), maximum cumulative gas production (mL/g DM), gas production fractional rate (h-1) and lag (h) were quantified. Inverse relationships between MPS and peak absolute rate of gas production, defined as the dependent and independent variables, respectively, were evaluated using linear and nonlinear models to facilitate calculation of MPS that potentially differed in fermentation effectiveness. For dry corn, the MPS-ASAE and MPS-FARM methods yielded similar estimates of MPS, but MPS-FARM overestimated MPS for high-moisture corn by about 495 um relative to MPS-ASAE. As a result, relationships between peak absolute rate of gas production and MPS-ASAE were explored. Peak absolute rate of gas production accounted for 71 and 85% of the variation in MPS-ASAE for dry and high moisture corns, but relationships were potentially corn-type dependent. Mean particle size unaccounted for by peak absolute rate of gas production was calculated as a relative residual (rr) MPS and found to be best related to prolamin protein (r = 0.57) and NH3-N (r = 0.64) for dry and high moisture corns, respectively. For dry corn, rrMPS was estimated as: rrMPS = 54.1 + (-17.7 * prolamin protein), where prolamin was expressed on a % of DM basis. For HMC, rrMPS = 6.06 + (9.6 * NH3-N), where NH3-N was expressed on a % of total N basis. Effective MPS (eMPS) of dry or HMC was then calculated as eMPS = MPS-ASAE - (rrMPS/100 * MPS-ASAE ). Peak absolute rate of gas production for dry and high moisture corns accounted for 90 and 95% of the variability in eMPS and removed a majority of the bias between corn types. Relationships between MPS and in vitro gas production parameters of dry and high moisture corns were improved by enhancing MPS measurement precision and adjusting MPS for chemistries that define fermentation effectiveness of particles.