Following my last blog on the use of immunoglobulins from hyper-immunised eggs as a means of controlling diarrheas and replacing animal plasma, I have received many emails asking me how animal plasma works and on what grounds egg immunologlobulins can replace it. I think we should take time this week to discuss this issue!
First, let me say this before anything else. There is no 100% precise explanation on how animal plasma actually works. There are many theories and different data supporting each theory. Then, there is personal experience and common sense. I am offering here my interpretation of scientific literature.
So, to begin with, let's dispel the myth about animal plasma having a 'taste' effect. First, data to such an effect are very ambiguous, in that they are open to more than one interpretation due to unclear experimental designs. Common sense also tells that had plasma had any 'taste' effect, this response would be dependent on ingredient composition of the formula plasma was used in. In truth, plasma response depends on base animal growth performance and similar effects are seen with 'bad' and 'good' formulas!
Second, there is a notion that animal plasma's effect is due to its highly digestible amino acids. True, plasma protein is very digestible, but so is the protein of many other animal and even some vegetable proteins, all of which do not offer an effect comparable to that of animal plasma. Only in extremely poor formulas would animal plasma's high quality protein be of real benefit, but at what an extremely expensive price! So, when replacing animal plasma a high quality protein source is needed to cover the difference in amino acids.
Third, some have hinted, without even data, that it is the minerals and even the salt in plasma that enhance feed intake. True again, minerals are needed and piglets like their feed salty (check the work done by D. Mahan at The Ohio State University). But, responses to minerals are never so dramatic as those from plasma!
So, what is left?
Immunoglobulins and especially IgG. Plasma contains up to 15% IgG and this is quite unique among most if not all ingredients used in piglet nutrition. How immunoglobulin's work? Very simple...yet, very effective is their mode of action. They neutralize pathogens so that they cannot attach themselves to the intestinal mucosa to exert their harmful properties.
Therefore, the closer the match between IgG and the pathogen (here the lock and key analogy fits very well), the better the effect. And, it is the generic nature of IgG in plasma that prevents it from being effective against pathogenic diarrhoeas. As plasma contains low levels of a wide plethora of most generic IgG for a great range of pathogens, when piglets are truly hit with an E. coli infection, plasma derived IgG are not enough to overwhelm the invading pathogens.
Here is where egg-derived immunoglobulins from hens immunised against specific piglet pathogens are at their strongest controlling diarrhoea. Have a look at the table below where infected piglets (challenged with K88) animals receiving different levels of egg antibodies experienced less days of diarrhoea and higher survival rates compared to negative control (adapted from Infection and Immunity, 1992, Vol (60):998). And, following that, a couple photos showing the dramatic effect of enterotoxemic E.coli infection and the protection offered by egg antibodies.
Negative egg IgG
A study conducted many years ago (3 identical trials), but never got much publicity, at the Iowa State University by R. Gatnau at Dr. D.Zimmerman's laboratory clearly demonstrated that the heavy-molecular-weight fraction of plasma (the one containing IgG) is responsible for its beneficial effects. Other fractions were of without any consequence (see graph, adapted from Journal of Animal Science, 1995, Vol 73(1):82).
In addition to this report, I have seen at least four more to the exact same effect all pointing to the fact that IgG are the active component in animal plasma. Looking at the data again while writing this blog, I now notice that pure immunoglobulins almost invariably give numerically superior performance to that of plasma across all trials. This was something that puzzled me in my own trials but I dismissed it as biological 'noise'. Is there something in pure immunoglobulins making them even more effective than plasma... More research is needed for sure!