Acids are generally applied to forages either to improve the degradability of poor quality cereal crop residues or to enhance pH reduction during ensiling. They are also used as dietary supplements to help maintain blood pH. The addition of either hydrochloric or sulphuric acid to cereal straws reduces hemicellulose content but has little effect on either cellulose or lignin. However, digestibility and intake improve and so, like alkali treatment, acid treatment may hydrolyse the ester bonds between lignin and the other cell wall polysaccharides. Again like alkali treatment, acid treatment improves degradability, but suffi- cient dietary protein must be supplied to ensure that this potential can be realized. Animals consuming cereal straw treated with acid and urea have been shown to have both an enhanced flow of microbial protein to the small intestine and increased nitrogen retention. An additional benefit identified with this combined treatment is that acidification appears to enhance the degree of ammoniation of straw by the urea. When sulphuric acid is used, the sulphur content of the treated material increases, which may be beneficial as sulphur is a vital element in the production of microbial protein. It is generally recommended that where additional nitrogen is supplied, sulphur should be provided at a ratio of S:N of about 1:12. Short-term treatment of cereal straw with organic acids such as formic acid have no effect on either digestibility or intake, with the acids being degraded in the rumen to methane and carbon dioxide.
The most common use of acids is their incorporation into the herbage mass to enhance the rate of pH reduction during ensiling. Successful preservation of plant material as silage depends on rapidly achieving a controlled fermentation under anaerobic conditions and the conversion of water soluble carbohydrates to lactic acid. At pH 3.8 to 4.3, microbial activity is inhibited, resulting in well-preserved, stable silage. When the crop and conditions within the silo permit, no additives are needed; but where either these are inadequate or to minimize losses in fermentation, the desired pH can be partly achieved by direct acidification. This promotes a lactic acid fermentation and lowers the energy cost of fermentation. A.I. Virtanen of Finland first developed the use of acids in this way in the 1930s. In what became known as the AIV method, combinations of sulphuric and hydrochloric acids were added to forages at ensiling to encourage the rapid reduction of pH (< 4) so as to suppress proteolytic activity. A number of acid-based silage additives are now available. For safety and to limit their corrosive effect, weaker organic acids such as formic acid are used, either alone or in combination with fermentation inhibitors such as formalin. The application of acids has been shown to increase animal performance, due to reduced losses of nutrients as well as improved protein quality, palatability and intake.
The most common use of acids is their incorporation into the herbage mass to enhance the rate of pH reduction during ensiling. Successful preservation of plant material as silage depends on rapidly achieving a controlled fermentation under anaerobic conditions and the conversion of water soluble carbohydrates to lactic acid. At pH 3.8 to 4.3, microbial activity is inhibited, resulting in well-preserved, stable silage. When the crop and conditions within the silo permit, no additives are needed; but where either these are inadequate or to minimize losses in fermentation, the desired pH can be partly achieved by direct acidification. This promotes a lactic acid fermentation and lowers the energy cost of fermentation. A.I. Virtanen of Finland first developed the use of acids in this way in the 1930s. In what became known as the AIV method, combinations of sulphuric and hydrochloric acids were added to forages at ensiling to encourage the rapid reduction of pH (< 4) so as to suppress proteolytic activity. A number of acid-based silage additives are now available. For safety and to limit their corrosive effect, weaker organic acids such as formic acid are used, either alone or in combination with fermentation inhibitors such as formalin. The application of acids has been shown to increase animal performance, due to reduced losses of nutrients as well as improved protein quality, palatability and intake.
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