Six steps to remove plasma from piglet feeds

Whether or not porcine plasma contributes to the on-going spread of the porcine epidemic diarrhea (PED) virus in piglets is still unclear. Yes, the PED virus has been detected in samples of plasma, but it is too early to conclude if this is enough to infect piglets eating diets manufactured with contaminated plasma.

Whether porcine plasma contributes to the ongoing spread of the porcine epidemic diarrhea (PED) virus in piglets is still unclear. Yes, the PED virus has been detected in samples of plasma, but it is too early to conclude if this is enough to infect piglets eating diets manufactured with contaminated plasma. Nevertheless, there is a growing demand for information on how to remove plasma from piglet diets to develop a contingency plan or adopt a business zero-risk policy before it is too late.

Lamentably, plasma is not a simple protein that can be just replaced on a protein (amino acid) basis by simple reformulation. It is a unique and complex ingredient – and a very expensive one at that — that improves feed intake and growth in piglets by as much as 50 percent. This is not something easily achieved by any other ingredients or additives. Indeed, the availability of plasma for almost 25 years has enabled nutritionists to design simple diets that are inexpensive, yet support acceptable performance. And, here is where the main problem in replacing plasma can be identified, because we need to bring back those ingredients that used to make piglet feeds work without plasma.

Introduce immunoglobulin substitutes

Research conducted by the same group that discovered plasma also revealed its true mode of action. It was determined, and then verified repeatedly by other university studies, that plasma improves gut health through its immunoglobulin content (Figure 1), which can amount up to 20 percent in total dry matter. This enhanced gut health allows piglets to grow faster; this in turn leads to higher feed intake. Indeed, feeding plasma to piglets of high health status is deemed ineffective, but such piglets are hard to encounter in commercial practice.

To replace the immunoglobulin fraction of plasma, the only real alternative is similar immunoglobulins that can be derived from bovine colostrum, whey proteins and egg immunoglobulins. Alas, colostrum is even more expensive than plasma and quantities are always limited. Whey immunoglobulins are weak and non-specific — plus excess whey protein concentrate increases pellet hardness beyond acceptable levels. On the other hand, designer egg-derived immunoglobulins – specific against piglet pathogens – have been shown to be an effective replacement of plasma (Figure 2), and are currently commercially available – again, at a considerable cost, but without the issues surrounding plasma.

Add a highly digestible protein fraction

Removing plasma from simple diets and replacing it with egg-derived immunoglobulins is rarely effective because the highly digestible protein in plasma should also be accounted for. Here, it should be mentioned that piglets require a highly digestible feed, in general, to thrive, but they have no specific need for the generic proteins in plasma (immunoglobulins are also proteins). This generic protein fraction can be replaced by other, equally digestible, sources of proteins, such as whey protein, soy protein isolate, pea protein, wheat gluten, potato protein, fish meal, etc. 

Indeed, adding any such protein source to a simple diet never brings about the dramatic effects of plasma, which further enhances the notion that it is not the protein quality in plasma that enhances growth performance in piglets. Following an old rule of thumb from the days before plasma, it is recommended to have a minimum 4 percent of animal protein in Phase I diets and 2 percent in Phase II diets. Today, of course, this requirement can be met from highly purified vegetable protein sources. 

Finally, it needs no reminder, but it is worth mentioning, that purified amino acids that have 100 percent digestibility can be used to replace part of the protein in plasma. This is true assuming L-Lysine-HCl does not exceed 0.5 percent in the final feed and total crude protein concentration is not decreased by more than 2 percentage points by the removal of plasma.

Glutamine benefits gut health

Glutamine is a unique amino acid in that it can help restore damaged gut epithelium tissue and enhance overall immunity status of the gut, which is beneficial when piglets are offered low-quality diets that depress appetite. But, for glutamine to be effective, concentrations should exceed 0.5 to 1.0 percent in the complete diet, something rarely achieved by common plasma levels.

In fact, glutamine supplied by 4 percent plasma in feed is about 0.3 percent, which is well below the minimum recommended level of supplemental glutamine. Nevertheless, if glutamine is required, then wheat gluten (27 percent glutamine) can be used to provide this special amino acid.

Bring in the lactose

Research has indicated that diets based on plasma do not require as high levels of lactose as diets without plasma. In fact, about 5 to 10 percent of lactose can be removed when high levels of plasma (4 to 6 percent) are employed in Phase I diets and about half of that in Phase II diets. 

Since plasma emerged, there has been a gradual decrease in the lactose levels in most commercial piglet feeds. Now, if plasma is to be removed, lactose levels should be re-evaluated to ensure piglet requirements are met. In general, for the U.S. market, levels of about 15 percent and 10 percent lactose in Phase I and II diets, respectively, should be considered as absolutely minimum in any diet devoid of plasma. In fact, an extra 5 percentage points of lactose would ensure high levels of acceptance — especially for Phase I diets. 

Of course, instead of lactose, it is possible to use other simple sugars, such as dextrose, maltodextrins, fructose, sucrose or molasses (on a lactose equivalent level).

Supplement the sodium

Plasma is rich in sodium. When removing it from a formula, this nutrient must be enhanced by adding salt or any other source of sodium. Fish meal is rich in sodium, but salt is usually the least expensive option. If high sodium levels were employed in a plasma-based diet, e.g. 0.35 percent Na, and then lower levels are accepted in the plasma-devoid diet, e.g. 0.25 percent, growth performance might be negatively affected, even though the new sodium level is still above minimum requirement of 0.20 percent. 

Research has demonstrated that in Phase I and II diets, piglets benefit from extra salt, up to 0.4 to 0.5 percent, under certain (yet unclear) circumstances. Thus, it is important to maintain sodium levels in commercial diets when reformulating to remove plasma. 

Finally, it should be noted that sodium bicarbonate should not be used as a sodium source in piglet diets because it buffers the already limited acidity in the stomach, resulting in reduced protein digestibility, resulting in pathogenic diarrheas.

Enhance the taste of the feed

The first obvious “symptom” of feeding plasma-based diets is enhanced feed intake. Many believe this is due to its meaty taste, but research has demonstrated that this is not actually true — taste has nothing to do with the beneficial effects of plasma. 

Indeed, meat flavors (umami) have not been able to improve feed intake to levels sufficient to compete with plasma. Nevertheless, we cannot deny plasma imparts a “good” taste in simple diets or diets with off-flavors. If this is the case and plasma is removed, feed intake will drop, albeit slightly, unless we also replace this feature. Adding an artificial flavor can mask certain off-flavors, whereas using “tasty” ingredients (whey, sucrose, cooked cereals, extruded soya, fish meal) can bring back the taste factor in simple diets.

Replacing plasma is difficult, if only because it has enabled nutritionists for too long to depend on simple diets. To effectively replace plasma, we must get back to technology used before the advent of plasma, and study again how to construct a high-quality diet from scratch. In fact, certain European manufacturers of piglet feeds never adopted plasma because their diets were “tasty” or “complex” enough that plasma never managed to improve them.

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