Ruminants bypass protein

There are four primary reasons why the mechanical extraction process is still selectively used. First, the mechanical extraction process can be furnished in very small scale, as low as 10 tons per day. The capital cost for small mechanical extraction facilities is considerably less than small solvent extraction facilities. In remote locations, freight differential can compensate for higher operating costs and lower yields. Second, there is a niche, high-value market for natural oils that have not been in contact with solvents or chemicals, requiring the use of mechanical extraction. Third, mechanical extraction can create a high bypass protein meal for ruminant animals that sells at a price premium over solvent extracted meal. Finally, mechanical extraction is often considered more reliable than solvent extraction when processing difficult materials (copra and palm kernel) in hot, tropical climates. 

Ruminants. Aldrich and Merchen (27) studied the effect of heat treatment of whole soybean on protein digestion by mminants. They reported that increasing the extmsion temperature from 220°F to 320°F at 20°F increments resulted in a linear decrease of in situ degradation of soybean protein. As expected, raw soybean protein degraded very fast. The extent of degradation was 84.1%, 45.7%, 40%, 40.9%, 36.7%, and 30.4% for the raw, 220°F, 240°F, 260°F, 280°F, 300°F, and 320°F treatments, respectively. In other words, extmded soybean at 320°F had a bypass protein value of 69.6% as compared with 15.9% for raw soybeans. 

Not all dietary proteins are degraded by the microbial population, and some pass unaltered or with minimal alteration into the small intestine where they are digested much as in a nonruminant animal. Dietary proteins that are not degraded by the ruminal microbes are referred to as rumen-undegradable protein (RUP NRC, 2001). This fraction also is sometimes referred to as escape or bypass protein. The total amount of protein that reaches the intestine for digestion is the sum of microbial protein and RUP, and is called metabolizable protein (MP NRC, 2001). This is the actual supply of digested proteins that furnishes AAs to the animal. 

Although tannins appear to protect protein from microbial attack in the rumen, their ultimate effects on ruminant nutrition may depend upon how available this bypass protein is to the animal. According to Price and Butler (1980), the same factors that cause tannins to have a deleterious effect on monogastric nutrition, will presumably be important in the post-rumen digestive tract. If the tannin-protein complex does not dissociate in the abomasum or intestine, there will be no benefit to the animal from the protein having been protected in the rumen. If it does dissociate, the liberated tannin may damage the intestinal tract or form new complexes at some point with endogenous proteins. 

Poos, M.I. T.L. Hanson T.J. Klopfenstein. Monensin effect on diet digestibility, ruminal protein bypass and microbial protein synthesis./. Anim. Sci. 1979, 45, 1516-1524. 

---