Adding animal plasma to piglet nutrition is known to improve weight gain and feed intake up to 50% - so its beneficial effects are indispensible. This feed additive, however, also comes with some major issues. Knowing its mode of action enables nutritionists to bypass these problems.
It was in the early 1990s when the beneficial effects of animal plasma on piglet growth and feed intake were first reported in the scientific community. In fact, the first report (Gatnau and Zimmerman, 1990) revealed an extreme response to diets with animal plasma (Table 1) compared to diets based on whey, or even skim milk, both of which were considered, at the time, top ingredients for piglet diets. This magnitude of response, around 50% over the unsupplemented diet, continued for some time until further work brought to the scene the benefits of using other complex ingredients. Today, in complex diets the response to animal plasma is reduced to about half of what it used to be back then. Nevertheless, animal plasma continues to be an integral part in many piglet nutrition programmes, worldwide, having reached an almost ‘indispensable’, but not indisputable status.
Issues with animal plasma
Indeed, nothing is perfect, and animal plasma comes with its own issues, which create considerable problems for field nutritionists. The two major issues with which animal plasma is faced today are:
Extremely high price
Among protein sources, animal plasma is the most expensive per unit of protein (or amino acids). With an average price of €3-4/kg, and an average inclusion range of 5%, in first-stage piglet diets, it is clearly evident that animal plasma costs about €150-200/ metric tonne of complete feed. This can easily account for up to one-third of total ingredient cost. Without doubt, this is a huge expense for any ingredient or additive. Currently, with the ongoing tight economic situation, animal plasma is pricing itself out of many piglet formulas, with the inevitable (but preferred) depression in piglet growth performance.
Possible carrier of diseases
Work conducted at Kansas State University (USA) has revealed that sterilised plasma supports even greater animal performance than normal, commercial, animal plasma. This was deemed as an indication of animal plasma being a possible carrier of certain pathogens or antigens that cause a subclinical activation of the immune system that reduces growth performance. This is currently disputed by plasma suppliers, but the fact remains that animal plasma was banned in the European Union for a number of years because it was considered a carrier of the ‘mad cow’ disease prions. Up to this day, animal plasma is prohibited from all diets for ruminants in the European Union. This last fact alone precludes the use of plasma in many feed plants where there cannot exist a separate line for production of piglet products containing animal plasma.
Clearly then, it is imperative to look for a viable alternative, but first we must understand how animal plasma works so that we can replace its most important function with success.
Erroneous theories on plasma
There have been a number of theories on how animal plasma works in piglet diets. Most of them have been tested and rejected, others remain untested. The three most important theories are:
Highly digestible protein
Indeed, animal plasma’s protein digestibility is high, around 90%, and comparable to the digestibility of other animal proteins, such as fish meal, blood meal, poultry meal, and dairy proteins, such as whey protein and casein. Yet, none of these alternative animal proteins are capable of improving animal performance to the extent that animal plasma does; often even when added on top of such ingredients. If it were protein digestibility that lies behind animal plasma’s properties, then it would be easy to replace it with crystalline amino acids, which are 100% digestible – lamentably, this is not the case!
High glutamine concentration
The amino acid glutamine has been implicated in improving gastrointestinal health in recently weaned piglets, especially those with disease or other gastrointestinal stress issues. This has been demonstrated in a number of scientific trials, but there is still considerable debate regarding its relevance under practical conditions. Nevertheless, the protein in animal plasma contains about 10% glutamine (so, animal plasma with 70% to 80% protein contains 7%-8% glutamine on an as-is basis). At 5% inclusion rate in a typical piglet diet, animal plasma brings about 0.35% extra glutamine to the complete diet. This is on par with what has been reported in glutamine trials (0.5%-1.0% is required for any effect to be easily discerned). In fact, wheat gluten protein (which contains about 25% glutamine) has been shown to partially replace animal plasma, but not totally. Thus, we can conclude that animal plasma is indeed a good source of glutamine, and perhaps part of its effect is due to glutamine, but as not all piglet diets require supplementation with glutamine, we can not ascribe the whole benefits of animal plasma to this amino acid alone. For those diets that require glutamine supplementation, wheat gluten is a less expensive alternative.
Improved taste characteristics
There is no doubt, animal plasma is a tasty ingredient. But, so are other sources of (good quality) animal proteins, such as fish meal and even (small quantities) of blood meal. Yet, as in the case of protein digestibility, none of these alternative ingredients can replace animal plasma based on taste alone. In fact, there are certain commercial ‘flavour’ products that try to mimic the taste effect of animal plasma, but these have not enjoyed the success many expected.
In addition, a scientific study (Ermer and others, 1994) has clearly indicated that it is not improved ‘taste’ that drives piglets in consuming greater quantities of diets with animal plasma. In fact, without given a choice, piglets will consume the same amount of a good quality with or without any flavours (of course, this is a generalisation based on a large number of trials).
As it happens, the exact mechanism of how plasma works has been elucidated by the same pioneer workers who first discovered animal plasma. In an ingenious research effort, Gatnau and Zimmerman (1995) fractioned animal plasma in its component parts: albumin, immunoglobulins, and the rest. They then compared each part against plasma, and against casein as a negative control. The results were unequivocal (Table 2): only immunoglobulins were able to replace animal plasma.
Here, we should mention as a reminder, that immunoglobulins are the ultimate weapon of the animal’s natural immune system. They are designed to attach to specific pathogens resulting in their elimination. Apparently, providing an external source of immunoglobulins aids the animal’s natural immunoglobulins to clean the gastrointestinal system better, resulting thus in higher health. It is already known and well-proven that healthier animals eat more because they have the ability to grow more (and not vice versa as it was up until recently the common notion), and this further explains the apparent increase in feed intake with diets based on animal plasma. The work of Gatnau and Zimmerman was later verified by other researchers with the exact same conclusion (Figure 1). Nevertheless, with the exception of one, Pierce and others, 2005, the rest of these reports were published only as abstracts in the Journal of Animal Science (USA); and as such they were soon forgotten (as it is usual with almost all abstracts), perhaps because at that time there was no practical way to either isolate or replace the immunoglobulins part of animal plasma.
Today, with the need to replace animal plasma more pressing than ever, we have one more way of verifying its mode of action. Egg immunoglobulins produced by hyper-immunised hens (against specific piglet pathogens) have been tested against animal plasma with seminal success.
This has been demonstrated not only under research conditions (Table 3) but also under practical, commercial situations (Table 4). In fact, the use of egg immunoglobulins has reached a high level of recognition among industry professionals as the only true replacement of animal plasma.
Especially in Europe, most piglet products of high quality today contain exclusively only egg immunoglobulins, instead, or in some distinct cases, even in addition to plasma. In fact, egg immunoglobulins offer four advantages over animal plasma:
• They are clearly less expensive, with savings up to €100/metric tonne of complete feed being possible;
• They carry none of the disease/BSE transmition risks of animal plasma;
• They contain a standardised level of immunoglobulins (whereas in animal plasma this depends on the chance exposure of slaughter animals to pathogens); and
• Egg immunoglobulins are specific against piglet diseases (by design), again, as compared to the chance mix found by necessity in any animal plasma source.