Effects of overnight wilting and additives on the fatty acid profile, α-tocopherol and β-carotene of whole plant oat silages

The aim of the present study was to clarify whether the 3 advised additives (sodium caseinate, SC; propionic acid additive, PA; and tert-butylhydroquinone, TBHQ) could reduce the losses of polyunsaturated fatty acids (PUFA), α-tocopherol and β-carotene in wilted (overnight wilting for 14 h) and non-wilted whole plant oats (Avena sativa L. cv. Esk, dough stage) silage after ensiling for 100 d. Harvested whole plant oats from the 5 fields (100 m² per field) were separately ensiled according to the following experiment design: 2 wilting levels (whole plant oat with and without overnight wilting were named as WWO and FWO, respectively) × 4 additives (without additive as the control, and with the 3 advised additives) × 4 copies per treatment. The additives-treated FWO and WWO were separately filled in silos (polyvinyl chloride bottle, 1 L), immediately. After ensiling for 100 d at room temperature, silos were opened and silages were sampled. Overnight wilting didn’t influence the contents of linoleic acid (C18:2n6) (P > 0.05), α-linolenic acid (C18:3n3) (P > 0.05) but resulted in losses of α-tocopherol (20.8 %) (P < 0.05) and β-carotene (27.4 %) (P < 0.05) in whole plant oats before ensiling due to multiplication of microbes, e.g., aerobic bacteria and yeasts. Compared with additive-untreated FWO silage, poorer fermentation quality was found in additive-untreated WWO because lactic fermentation was weakened while butyric fermentation was stimulated. Compared with the material before ensiling, ensiling increased contents of C18:2n6, C18:3n3 and PUFA either in FWO or WWO silage (P < 0.05) due to the high ratio of volatile fatty acids to lactic acid. The ensiling increased β-carotene loss (P < 0.05) but accumulated α-tocopherol in either FWO or WWO silage (P > 0.05). Moreover, only PA improved fermentation quality of FWO and WWO silages, demonstrated by the lowest pH and ammonia-N content and the highest lactic acid content (P < 0.05), and preserved C18:2n6, C18:3n3 and PUFA in FWO silage. All additives did not reduce α-tocopherol loss either in FWO or WWO silage but decreased β-carotene loss in FWO silage. In conclusion, using advised additives did not reduce the oxidation losses of PUFA, α-tocopherol, and β-carotene in overnight wilting whole plant oat silages, and PA is a potential additive to improve fermentation quality and preserve main PUFA, α-tocopherol, and β-carotene in non-wilted whole oat silages.