26 Oct 2010
Grass silage is a roughage fodder which many organic farms feed to pregnant sows. The nutritional value of grass silage is important in order to be able to responsibly use it as a replacement for mixed feed. By including corn cob mix (CCM) with the grass silage, it is possible to replace an even larger amount of mixed feed with mixed silage. For this reason, Wageningen UR has studied the chemical composition, digestibility and energy value (EV) of different grass silages of varying qualities and of CCM for organically-kept pregnant sows.
The study was carried out on the experimental pig farm Raalte. A plot of grass with very little clover was subdivided into five sections which were mown for the first time at different points in the spring. This resulted in five different grass silages which varied in quality. They contained respectively 1.8 tonnes, 2.2 tonnes, 3.1 tonnes, 3.9 tonnes and 5.0 tonnes of dry matter per hectare. Sows seem to prefer grass silage with a low dry matter content. Therefore a dry matter percentage of 25% was aimed for in the grass silage.
The control group received 2.31 kg dry matter from mixed feed daily. The test groups on grass silage or CCM received 0.88 kg of dry matter from mixed feed and 1.43 kg of dry matter from grass silage or CCM. The actual amount of dry matter ingested from grass silage was 200 to 300 grams per day less than planned. The sows were fed twice daily.
Energy value
In the grass silages studied, the dry matter content measured between 21.3 and 24.9% and the EV per kg of dry matter measured between 0.78 and 0.95. The EV per kg of dry matter and the EV intake were highest in the case of grass silage with a dry matter yield of 2.2 tonnes per hectare, and lowest in the case of grass silage with a dry matter yield of 2.0 tonnes per hectare. The EV per kg of dry matter for CCM is 1.49.
It appears that, for the grass silages, there are relationships between crude protein content, lactic acid content, sugar content, NSP content and dry matter yield per hectare on the one hand and EV per kg of dry matter on the other hand. It appears that optimal values do exist for these relationships. If the value is higher or lower, the EV falls. This makes it difficult to calculate the EV purely on the basis of the chemical composition of the grass silages.
Follow-up study
A follow-up study will examine how much grass silage and mixed silage (grass mixed with CCM and grass mixed with barley) pregnant sows ingest if they have unlimited access to it in addition to receiving a set amount of mixed feed. The results of this study will be published at the end of the year.
Download the report
Report 342, “Digestibility and nutritional value of grass silages of varying quality and of CCM for organic sows,” by C.M.C. van der Peet-Schwering et al. can be downloaded for free via http://edepot.wur.nl/150497.
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