Effects of a propionic acid-based preservative on storage characteristics, nutritive value, and energy content for alfalfa hays packaged in large, round bales

Authors: Coblentz, Wayne; BERTRAM, MICHAEL - University Of Wisconsin

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2011
Publication Date: 12/21/2011
Citation: Coblentz, W.K., Bertram, M.G. 2011. Effects of a propionic acid-based preservative on storage characteristics, nutritive value, and energy content for alfalfa hays packaged in large, round bales. Journal of Dairy Science. 95:340-352.

Interpretive Summary: Past studies have shown that there are clear benefits derived from applying propionic acid-based preservatives to alfalfa hay packaged in small, square bales. To see if it would have the same benefit with large bales, a propionic acid-based preservative was applied to large, round bales of alfalfa hay packaged at initial moisture concentrations ranging from 10.2 to 40.4%. Although normal heating characteristics were clearly altered by acid treatment, overall positive effects on post-storage nutritional value were limited. This could be related to the greater size of the bale packages, differences in application methodologies between round and square (plunger-type) balers, or other factors. For these large (1.5-meter diameter) round-bale packages, the potential to improve forage quality relative to cost of application was not especially favorable, and forage producers may find that diligence to achieve adequate field drying prior to baling, or use of oxygen-exclusion methods such as wrapping in plastic, may be better alternatives for preserving moist hays.

Technical Abstract: During 2009 and 2010, alfalfa (Medicago sativa L.) hays from two cuttings that were harvested from the same field site were used to evaluate the effects of a propionic acid-based preservative on the storage characteristics and nutritive value of hays stored as large, round bales. A total of 87 large, round bales (diameter = 1.5 m) were included in the study; of these, 45 bales served as controls while 42 were treated with a buffered propionic acid-based preservative at mean application rates of 0.5 ± 0.14 and 0.7 ± 0.19%, expressed on a wet (as is) or DM basis, respectively. Initial concentrations of bale moisture ranged from 10.2 to 40.4%. Internal bale temperatures were monitored daily during an outdoor storage period, and heating characteristics were summarized for each bale as heating degree days > 30oC (HDD). Accumulations of HDD for all bales were regressed on initial concentrations of moisture. For acid-treated bales, the regression relationship was best fitted to a quadratic model in which the linear term was dropped to improve fit (Y = 2.02 x2 – 401; R2 = 0.765); control hays were best fitted to a nonlinear model in which the independent variable was squared [Y = 4112 – (4549 * e-0.000559x*x); R2 = 0.766]. Acid-treated bales exhibited reduced maximum internal bale temperatures, especially following the 2010 harvest, but often maintained elevated bale temperatures for a longer period of time than control hays. Based on these regressions, acid-treated bales accumulated more HDD than control hays when the initial bale moisture was > 27.7%. Linear regressions of recoveries of DM on HDD did not differ (P = 0.230) on the basis of acid treatment, yielding a common linear relationship of Y = -0.0066 x + 96.3 (r2 = 0.753). Recent research with large-round bales that relates changes in concentrations of various nutritional components to heating characteristics has shown that these regression relationships are often curvilinear, and they frequently exhibited asymptotically defined limits within severely heated hays. These general characteristics were corroborated in the present study; however, regression relationships for changes (post-storage or pre-storage) in concentrations of several nutritional components (NDF, cellulose, lignin, ash, CP and TDN) within acid-treated hays exhibited more inflection points or were higher-ordered polynomial regressions than those of control hays. These generally more complex regressions may reflect the perturbation of normal heating patterns following acid treatment; however, overall effects on post-storage nutritive value were relatively limited in scope. Past studies have demonstrated clear benefits from application of propionic acid-based preservatives during packaging of alfalfa hay in small-square bales; however, our results with large, round bales were much less favorable. This could be related to the greater size of the bale packages, differences in application methodologies between round and square (plunger-type) balers, or other factors. Regardless, the potential to improve nutritive value relative to cost for these very large (1.5-m diameter) round bale packages was not especially favorable, and producers may find that diligence to achieve adequate field desiccation prior to baling, or use of oxygen-exclusion methods such as wrapping in plastic, may be better alternatives for preserving moist hays.