Controlling aerobic stability of grass silage-based total mixed rations

Vigorous growth of aerobic microbes in feed, resulting in heating of total mixed rations (TMRs) and reduced feed quality, is a relatively common problem for ruminant livestock production. Two experiments were carried out to examine the role of hygienic quality of raw materials and propionic and formic acid-based preservatives on the aerobic stability of grass silage-based TMR. In Experiment 1, the hygienic level of TMR was varied by an inclusion (1/10, w/w) of one-week-old TMR into the mixture. In Experiment 2, the level of hygiene was varied by inclusion or omission of brewers’ grains or by the quality of the grass silage (fresh or after aerobic exposure). In both experiments, a liquid preservative (propionic acid, ammonium propionate/formic acid and ammonium formate) or a solid preservative (sodium calcium propionate) was applied to the feeds at the time of TMR mixing at 0, 2 and 3 g/kg (Experiment 1) or 0, 2, 4 and 6 g/kg (Experiment 2).In Experiment 1, the aerobic stability of the TMR was reduced by 50 h by the inclusion of one-week-old TMR. In Experiment 2, the aerobic stability was reduced by ca. 30 h by the inclusion of aerobically spoiled grass silage. Conversely, the aerobic stability of the TMR improved by at least 30 h by omission of brewers’ grains from the mixture. Added preservatives improved aerobic stability of TMRs in both experiments. In Experiment 2, improvements in aerobic stability were sufficient to have practical value, and aerobic stability of the TMRs was linearly dependent of the dose level of liquid preservative. Improvements in aerobic stability were greater in the normal quality TMR than in the TMR prepared using silage that already showed some aerobic deterioration. Thus the use of preservatives does not provide a substitute for good hygienic quality of the feed ingredients.