Sugar in NorFor
The analyse method of sugar that is recommended by NorFor is the ethanol soluble carbohydrate (ESC). That method is quite similar to the more common water-soluble carbohydrate (WSC) method. The similarities are that monosaccharides like glucose and fructose, disaccharides and oligosaccharides are included in both ESC and WSC. The method of WSC also include all the fructans, while ESC includes only some part of the fructans. The part of the fructans that are included in the analysis by the ESC method, are the less polymerized ones.
Fructans are polymers of mainly fructose and grass use it to store energy. In the Nordic countries, cool-season grasses are used, and those grass varieties store more fructans than warm-season grasses.
Rumen load index
Fructans as a substrate in the rumen differ from substrates such as monosaccharides. Compared with monosaccharides, degradation of fructans is delayed in the rumen. Furthermore, the degradation rate is slower and end products such as lactate are rare (Hall & Weimer, 2016). The rumen load index calculated in NorFor is the ratio of easily degradable carbohydrates to total fibre and aims to show the effect of easily degradable carbohydrates on ruminal NDF digestion. Because sugar is included in the rumen load index, it makes sense not to include polymerized fructans in the sugar analysis as those fructans are less easily degradable than the mono-, di- and oligosaccharides.
NEL20 energy content
The method of analysing sugar can have quite a large impact on the rumen load index. On the contrary, the effect of the method of analysing sugar does not have a large effect on energy content after the update of the NorFor model in 2021. In October 2021 we changed the NorFor model quite substantially. When reviewing the outcome, we see that results of forage analyses are more stable, with organic matter digestibility (OMD) having the strongest effect on energy content. Sugar content in forage has much less effect on energy now than before (see Figure 1).
Figure 1. After the update of the NorFor model in October 2021, sugar content have almost no effect on the standard feed value of net energy at 20 kg dry matter intake (NEL20). This is shown with two forages of different levels of organic matter digestibility (OMD), “High OMD after” (79% of OM, solid black line) and “Low OMD after” (68% of OM, solid grey line) compared with before the update (black and grey dotted line, respectively).
The average sugar content analysed with the ESC method in Nordic forages is 59 ± 42 g/kg DM (mean ± standard deviation).
Read more about fructans
M. Hall & P.J. Weimer 2016. Divergent utilization patterns of grass fructan, inulin, and other nonfiber carbohydrates by ruminal microbes. J. Dairy Sci. 99:245–257. https://doi.org/10.3168/jds.2015-10417
Read more about the NorFor model update in 2021