Kindly advice me the the most appropriate method with international acceptance methods.
Method for Silage Samples
Scope:
Silages contain a volatile dry matter (DM) fraction that is lost with oven drying and freeze drying. This fraction contains volatile fatty acids, alcohols and volatile nitrogen (N) compounds. The loss of volatiles varies with the extent and type of silage fermentation, and is generally higher with low DM silages where there is usually a more extensive fermentation. With higher DM silages (> 50 % DM) there is a more restricted fermentation so the volatile loss on oven drying is less. As the volatile compounds in silage are completely digestible, it is important to take this into account when calculating digestibility, otherwise digestibility will be underestimated. Owing to volatile N losses, the total N content of silages will also be underestimated if analyses are conducted on oven dried samples. All other analyses on silages will be overestimated unless a correction is made for the volatile DM content.
Principle:
A laboratory reference method that specifically determines water content is needed to allow the calculation of the true DM content of silages and other fermented feeds. The Karl Fischer method has been found to be suitable and is now semi-automated through the use of Karl Fischer titrators. The method has been described by Kaiser et al.(1995) and involves the extraction of silage moisture in methanol, and then determining water content of the extract using a Karl Fischer titrator.
The above procedure, while suitable for research laboratories, is less appropriate for commercial feed testing laboratories. In this situation, an alternative approach is to use a correction equation(s) o predict true DM from an oven DM measurement. As the correction required will be influenced by the oven drying regime adopted, it is important that the correction equation selected is applicable tothe oven drying temperature used.
Procedure:
An earlier correction equation provided by Kaiser et al.(1995) calibrated true DM against oven DM determined at 80ºC. This was based on a relatively small number of silages. To increase the number and the range of silages, two correction equations have been developed at the Wagga Wagga Agricultural Institute, for silages oven dried at 80ºC for 24 hours (one-stage method) and at 60ºC for 24 hours (first stage of two-stage method,i. e. Partial DM).
(a) Correction for silages dried at 80ºC This correction equation has been based on 102 silage samples from studies at the Wagga Wagga Agricultural Institute (Kaiser et al.1995; Kaiser and Kerr 2003). The silages covered a wide range of crops and pastures with oven DM contents (80ºC) in the range 18.0-72.8 %.
Estimated True DM (%) = 3.846 + (0.96 × oven DM %)
(r2= 0.99; s.e. = 1.28)
(b) Correction for silages dried at 60ºC this equation is based on 60 ºC silage samples (a subset from the above study by Kaiser and Kerr2003). The silages covered a wide range of crops and pastures and had DM contents (60ºC) in the range 20.6-78.1 %.
Estimated True DM (%) = 4.686 + (0.89 × oven DM %)
(r2= 0.98; s.e. = 1.61)
References:
Kaiser, A.G. and Kerr, K.L. (2003). More Accurate Laboratory Tests for Assessing SilageQuality, Final Report for DRDC Project DAN 100 and RIRDC Project DRD-4A, 50pp.
Kaiser, A.G., Mailer, R.J. and Vonarx, M.M. (1995).J. Sci. Food Agric.
69: 51-59.
Kaiser, A.G., Bailes, K.L and Piltz, J.W. (2006). An Evaluation of Drying Regimes used to Determine Forage DM, Final Report for DRDC Project DAN 12109 and RIRDC Project DRD-5A, 22pp.
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