## 1 Introduction  
It is increasingly important to save energy in the food production chain. The world's population is growing and the challenge of feeding all people presupposes efficiency in every step of food production [1]. The aims of feed conservation as silage are maintaining quality and feeding characteristics of the fresh crop, and minimizing dry matter and energy losses [2]. Silage, which is used as feed for milk- and meat-producing animals, undergoes aerobic deterioration when it is exposed to air [3]. The diffusion of oxygen into silage in bales or clamp silos is unpreventable. Even in well-sealed silos on farms small amounts of oxygen diffuse into the silage. This inflowing oxygen is used as a source for microbial respiration, a process which proceeds along with dry matter losses. When the silo has been opened for feed-out the feeding surface of the silage is exposed to oxygen, leading to an increase in aerobic microbial metabolism. As a result heating of the silage and further losses of dry matter may occur [4; 5]. Spoilage of silage means energy losses, which should be prevented. The aerobic deterioration of silage is a worldwide problem for feed quality and farm profitability [6]. Along with an anaerobic environment, appropriate substrate and an adequate quantity of lactic acid-producing bacteria are needed to reach a quick drop in pH during ensiling, which is one of the most important requirements to reach high silage quality [2]. The quality of silage is often not optimal because the process of ensiling is dynamic and complex and can be influenced by many different factors [7]. [PERSON] and [PERSON] [5] give the advice of using additives if there is the risk that management requirements are not met. The use of homofermentative lactic acid-producing bacteria as silage inoculants has the aim to produce mostly lactic acid and fewer other fermentation products. As a consequence, the pH drops quickly [8]. Spoilage is caused by damaging microorganisms. Some of them are activated when coming in contact with oxygen, which leads to aerobic deterioration [3]. One of the common reasons for using additives is to inhibit aerobic microorganisms, especially those associated with aerobic stability [7]. Yeasts have been identified to be the primary initiator of aerobic spoilage. Lactic acid is not as effective in its antimyctical effect as propionic acid [8; 9]. In fact, lactic acid-producing bacteria used as inoculants have even been observed to decrease aerobic stability [9; 10]. Bacteria producing both propionic and lactic acids have great potential to be used as heteroformative inoculants [8]. A heteroformative _Lactobacillus_, producing lactic acid and acetic acid, which is also associated with the production of propionic acid, is _Lactobacillus buchneri_[7]. [PERSON] [10] describes _Lactobacillus buchneri_ to be the most consistent heteroformative concerning the improvement of aerobic stability, compared to others that are commercially available. The same prolonging and improving effects on aerobic stability as propionic acid applies to acetic acid. Acetic acid is an inhibitor of spoilage organisms and thereby increases aerobic stability. Heteroformative microorganisms producing both acetic acid and lactic acid are, e.g., _Lactobacillus rhamnus_ and _Lactobacillus plantarum_[11]. The objective of this study was to investigate the effects of different factors (biological, chemical, and physical) on silage during aerobic conditions. As a physical factor, different bulk densities were adjusted during ensiling. Silage density is one of the main physical factors, which affects the rate of oxygen inflow into the silage during feed-out [5]. There is an increasing desire to reach a high density of silage because a low void volume means a low initial air content. This can significantly reduce the risk of a temperature rise and the loss of dry matter and energy [12]. Two different biological inoculants (biological factors) were added to parts of the silage and a chemical additive (chemical factor) was also used.