Improved analytical capacity for determination of forage quality, utilising the gas production technique

Abstract: Voluntary intake and digestibility of forages are characteristics that affect the animal's performance (Mertens, 1994). Today there are several techniques that can be used for studying forage quality and from where the results can be correlated to feed intake and animal performance. The main factor that affects dry matter intake (DMI) is the energy requirement, which on the other hand is affected by environmental temperature, physical activity of the animal and the production level (Faverdin et al., 1995). Forage intake is mainly restricted by low digestibility, where the content of the cell wall constituents have the greatest impact on digestibility (e.g. Blummel & Becker, 1997; Mould, 2003). The gas production (GP) technique is an in vitro method that is a simple, relatively quick and inexpensive. In this method feed samples are incubated in buffered rumen fluid and the gas that is produced due to fermentation is recorded. The GP gives information on forage digestibility and rumen fermentation pattern (Getachew et al, 1997). Several authors have found high correlations between in vitro GP studies and DMI of forages (e.g. Blummel & Becker, 1997; Hetta et al., 2007). In the original method, the incubation time for GP analyses is 24 h (Menke et al. 1979), but today it is more common with incubation times between 24 h up to 96 h. The analytical capacity of the technique is affected by incubation time, as a smaller number of experiments can be conducted per time unit (week) in the laboratory. Studies on high quality forages have shown that 90 % of the gas that is produced during the incubation is produced within the first 24 hours (Hetta et al., 2003) and also that after 15 to 20 h of incubation, the GP decreases although it doesn't stop (Cone et al., 1998). Fifteen ensilage samples with known silage dry matter intake (SDMI) and chemical composition were analyzed with the gas production technique (Cone et al., 1996). Feed samples that have been analysed in this study are the same as the ones that were studied by Hetta et al. (2007). The aim of this study was to evaluate the consequences of reducing the length of incubation time from 72 h to 24 h for studies of high quality forages, utilizing the GP technique. Results from this study, with 24 h incubation, were compared to the results from the research by Hetta et al. (2007) where the incubation time was 72 h. A special focus in this study was put on the effects on reproducibility of the measurements, correlations with other feed parameters and silage intake of the forages. The results show that there is a great potential for improving the analytical capacity of the technique, by reducing the length of incubation from 72 to 24 h for studies on high quality forages. This study has shown that 24 h incubation gives informative results with high reproducibility of the measurements, clear relationships and high correlations between different parameters and feed intake, and also reliable models for prediction of silage intake with high values of the coefficient of determination.