Effects of a propionic acid-based preservative on storage characteristics, nutritive value, and energy content for alfalfa hays packaged in large round bales1

During 2009 and 2010, alfalfa (Medicago sativa L.) hays from 2 cuttings 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, whereas 42 were treated with a commercial propionic acid-based preservative at mean application rates of 0.5 ± 0.14 and 0.7 ± 0.19% of bale weight, expressed on a wet (as is) or dry matter basis, respectively. Initial bale moisture concentrations 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 (HDD) >30°C. For acid-treated bales, the regression relationship between HDD and initial bale moisture was best fitted to a quadratic model in which the linear term was dropped to improve fit (Y = 2.02x2 − 401; R2 = 0.77); control hays were best fitted to a nonlinear model in which the independent variable was squared [Y = 4,112 − (4,549 × e−0.000559x*x); R2 = 0.77]. Based on these regressions, acid-treated bales accumulated more HDD than control hays when the initial bale moisture was >27.7%; this occurred largely because acid treatment tended to prolong active heating relative to control hays. Linear regressions of recoveries of dry matter on HDD did not differ on the basis of treatment, yielding a common linear relationship of Y = −0.0066x + 96.3 (R2 = 0.75). Regressions relating changes (post-storage - pre-storage) in concentrations of several nutritional components (neutral detergent fiber, lignin, ash, crude protein, and total digestible nutrients) with HDD for acid-treated hays typically exhibited more inflection points or were higher-ordered polynomial regressions than those of control hays. These more complex responses probably reflected the perturbation of normal heating patterns following acid treatment; however, overall effects on post-storage nutritive value were relatively limited in scope. The potential to improve nutritive value relative to cost for these large round bales was not especially favorable, and hay producers may find that diligence to achieve adequate field desiccation before baling, or use of oxygen-exclusion methods, such as wrapping in plastic, may be better alternatives for preserving moist hays.