The relationship of silage temperature with the microbiological status of the face of corn silage bunkers

A method is proposed to quantify aerobic deterioration of corn silage forage quality as related to the temperature of silage mass in the bunker. Aerobic deterioration, apart from causing nutritional value losses, affects the hygienic quality of silages through the accumulation of pathogenic organisms and their toxins. A survey was carried out in northern Italy that involved a detailed examination of silage bunker from each of 54 dairy farms. Samples from the core, the peripheral areas within 1 m from the silo walls, and the molded spots, when present, were collected. The sample and silage temperatures across the working face were measured at depths of 200 mm at 11 locations and at 7 elevations. The temperature of the central zone of the silo was defined as the reference temperature (Tref40). The difference between the temperature of the silage sample and the Tref40 was used as a heating index associated with aerobic deterioration (dTref40). The working face area with visible molds was measured. The samples were analyzed for DM content; pH; water activity; nitrates; lactic, acetic, and butyric acids; and microbiological count of yeasts, molds, and clostridia spores. The core samples always showed a pH below 4.0 and a dTref40 below 2°C, whereas the silages from the peripheral areas were split into 2 groups, one that had a pH lower than 4 and a dTref40 lower than 3.5°C (53%) and one that had a pH higher than 4 and a dTref40 higher than 5°C (47%). Most of the silages from the peripheral areas (94%) and all the silages from the moldy spots that have a dTref40 above 5°C had a pH higher than 4.5. Furthermore, a positive dTref40 higher than 5°C corresponds to a higher yeast count than 5 log cfu/g in most of the silages from the peripheral areas (93% of samples) and in almost all the silages from the molded spots. The evaluation of the extension of the visible molded areas combined with temperature measurement at 200 mm behind the feed-out face could offer a good indication of the health status of silage during consumption. Furthermore, this method could be useful to detect early stages of the aerobic deterioration process and to improve silage management.