Towards improved silage quality--a review

Silage quality, as with all forages, is governed by the maturity of the crop at harvest. However, fermentation in the silo further influences nutritive value of silage by reducing voluntary intake and utilization of digestible nutrients. Silage research up to the present time has focussed on closing the gap between feeding value of the original crop and that of the resulting silage. This review focuses on the advances made towards closing that gap, and explores the possibility that in the future ensiling can become a tool for actually increasing the feeding value of forages. Following a section defining silage quality, the relationships between silage fermentation quality and voluntary intake and between silage fermentation and protein and energy utilization will be examined, with emphasis placed on measures to minimize the negative effects of fermentation on animal production. Recent literature is reviewed, which suggests that many factors previously thought to reduce silage intake, such as pH, lactic acid and dry matter (DM), have, in fact, only a casual relationship with intake. Concentrations of fermentation acids do not seem closely related to silage intake; however, they are critical in determining the balance of volatile fatty acids (VFA) produced in the rumen. This in turn, affects the non-glucogenic ratio and can influence milk and body composition in productive livestock. While rumen ammonia is often implicated in reducing silage intake, protein solubility may be more the causal agent than ammonia per se. Protein solubility is also a major factor in reducing the efficiency of silage protein utilization. Methods to reduce protein solubility in silages are discussed. Methods shown to improve silage feeding value include effective wilting and rapid acidification, either by direct acidification or the use of inoculants. Their widespread adoption has undoubtedly contributed to improvements in animal production from silages in recent years.