Hydrolyzed intestinal protein is a byproduct of heparin production from the human health industry. In brief, pig intestines are hydrolyzed and heparin is removed. In the process, sulfuric acid is used, and because of this, the byproduct, which is rich in protein, is also rich in sulfur.
Commercial practice and some unpublished research indicate a possible trend towards enhanced feed intake in piglets consuming this ingredient. Most likely, this is the effect of enhanced palatability (animal protein taste) in very simple diets and (or) the outcome of enhanced overall protein digestibility, which is known to drive up feed intake in piglets. It is certainly interesting that such evidence is coming especially from Eastern Europe, where formulas are very basic, lacking the complex ingredients seen in most Western Europe formulas. Regretably, undisputable research remains scarce.
Certain claims regarding replacing animal plasma remain without any scientific base, as the plasma effect is well known to be due to its high level of immunoglobulins; something not found in abundance in hydrolyzed intestinal protein. Most likely, the erroneous comparison is made because both ingredients provide the same end result, that of enhanced feed intake -- but for very different reasons.
The case of sulfur
The case of sulfur requires further attendance because there are certain products containing exceptionally high levels of this mineral, whereas in others, sulfur has been reduced -- but at a cost reflected in the final price. In essence, not all hydrolyzed intestinal protein products are the same.
Sulfur is, of course, an essential nutrient, but because it abounds in natural ingredients, no requirement has been established for it in use in commercial formulation. It is actually excess sulfur that often draws the attention, as it may be responsible for secretory diarrhea due to an osmotic effect in the gastrointestinal tract; today, research on this topic remains limited.
Nevertheless, researchers from Germany (Kamphues et al., 2002) investigated the effect of high sulfate concentration in 29 samples of whey on fecal consistency in pre-ruminant calves (that are comparable to piglets in terms of gastrointestinal maturity and function). Sulfur content in whey ranged from 0.03 to 4.3 percent per kg dry matter. A high concentration of sulfate in the liquid milk replacer diet resulted in marked increases in incidents of diarrhea. This concentration would be equivalent to about 0.3 percent sulfate per kg dry matter. If we assume results obtained with milk-fed calves are rather acceptable for piglets, it can be deducted that a safe level of sulfate in most piglet diets should be below 0.25 percent on an as-fed basis. This number can be used as a guide when evaluating any high-sulfur containing ingredient.