Relation between seal integrity and hygienic quality in silage bales and differences between baling techniques

Bale silage is widely used in many countries on small and medium sized cattle farms and for horses. About 8 million bales are produced annually in Sweden, corresponding to approximately 45% of the total silage production of 4.5 million ton DM (Pettersson, 2006; SCB, 2016). Sufficient protection against air intrusion during storage is essential in all ensiling, and since introduction of the round bale technique, seal integrity of bales has continuously been improved. When the technique to make silage in bales was introduced, bales were inserted in plastic bags but this was soon replaced by the stretch film technique. During the last two decades, the polyethylene industry has continuously developed new stretch film qualities which have been tested on round and square bales of grass at the Department of Animal Nutrition and Management, SLU. Degree of air-tightness of bales, seal integrity have been measured in these studies by the time it takes for an induced under-pressure to disappear in the bales. Silage quality has thereafter been analyzed in terms of standard chemical analysis of fermentation parameters such as pH, ammonia nitrogen and volatile fatty acids and hygienic standard in terms of cell counts of yeast and mould. The main purpose of the present work was to evaluate the relation between seal integrity, measured as pressure equalization time, and fermentation parameters and hygienic quality. Furthermore, data was used in a meta-analysis to study how silage quality was affected by number of stretch film layers and by using round- or square bales.