Comparative digestibility of nutrients from bio-ethanol production by sheep and pigs

Ruminants are known to better digest fibrous feeds than pigs. Byproducts from the bio-ethanol production based on grains are not only high in protein and fat, but consist for about one third of fibrous substances. Particularly dried distillers grains and solubles (DDGS) are rich in cell walls and are fed to both ruminants and pigs. One may question which animal is most efficient in digesting these feedstuffs. In total 18 byproducts were studied: 12 batches of DDGS (3 pure wheat, 3 pure maize and 6 mixed, originating from 7 European plants), 5 batches of condensed distillers solubles (CDS) (from 5 plants) and one mixture of CDS and wheat bran. Byproducts were fed in combination with hay or maize silage to sheep (in a ratio of 40/60 on DM-basis) or combined with a concentrate for pigs (30/70 ratio) and apparent digestibility was calculated by difference. Determination was with 5 mature sheep by total fecal collection and with 6 growing pigs after adding chromium oxide as indicator to the feed and by spot sampling of the feces. Digestion coefficients of crude protein (CP), crude fat (CFat) and organic matter (OM) was determined with both species, whereas fibre digestibility was based on NDF for sheep and on non starch polysaccharides (NSP) for pigs. The byproducts contained on average (per kg dry matter): 315 g CP (range: 205 – 495), 90 g CFat (60 – 148), 256 g NDF (43 – 366) and 326 g NSP (194 – 406). Mean digestibility of CP amounted to 75.2 vs. 76.2%, of CFat to 87.8 vs. 83.1%, of NDF/NSP to 68.5 vs. 52.5% and of OM to 81.4 vs. 76.2% in sheep vs. pigs respectively. The difference in digestibility as analysed by a paired t-test was not significant (p>0.05) for CP, but highly significant (p<0.001) for the other nutrients. These results confirm the better fibre digestibility by ruminants as compared with pigs, but the higher fat digestibility by sheep is rather unexpected. Moreover, the difference in fat digestibility increased linearly (p = 0.014) with higher NSP content.