Choosing immunoglobulins for piglet feed: milk, plasma or eggs

Immunoglobulins are anexciting, powerful, yet little acknowledged, component in modern piglet diets. Usingthem at the right amount and form can create the most competitive pigletformulas in terms of cost and animal performance.

Immunoglobulins are an exciting, powerful, yet little acknowledged, component in modern piglet diets. Using them at the right amount and form can create the most competitive piglet formulas in terms of cost and animal performance.

What are immunoglobulins?

Immunoglobulins are all-natural globular glycoproteins produced by all animals as part of their immune system. Immunoglobulins are the last and most powerful line of defense against invading pathogens, and as such, their production is quite taxing. Thus, they are only produced when the pathogens are not cleared by the first-line systems of defense. Immunoglobulins are designed to attack specific pathogens in a lock-key model, effectively “tagging” pathogens for elimination or destruction.

There are many classes of immunoglobulins (IgA, IgG, IgM, IgD, IgE, IgY). Some are involved in allergic reactions, others have a more local function, others are prevalent in milk and eggs, and yet others have a more widespread reach. There is a certain degree of overlapping in various functions, whereas species differences exclude IgG in birds to the preference of IgY. Egg immunoglobulins (IgY) are characterized by higher avidity (number of binding sites) and affinity (strength of attachment per molecule) compared to IgG, but otherwise, these two immunoglobulins perform the same functions.

Immunoglobulins exert their effects on pathogens in a number of ways. They can neutralize bacterial toxins by binding tightly and blocking a part of the toxin. They can also neutralize viruses by binding and blocking a system vital to their biological activities. In microbial infections, immunoglobulins bind to pathogens and inhibit their attachment to mucosal epithelial cells or cause agglutination (pathogens are eventually excreted) to the same effect. They may also activate the complement pathway (another part of the immune system), leading to destruction of the cell on which the pathogen may be attached. Finally, immunoglobulins can attract phagocytes that eliminate infected cells.

Immunoglobulins from milk products

We have been formulating piglet feeds with immunoglobulins since we first started using dairy products, specifically skim milk and whey powder. A good quality whey contains about 3-4 percent immunoglobulins (IgA), which although are of a weak “potency” still make their presence felt when whey is added at 20-30 percent in a piglet feed. Although IgA are an important source of immunoglobulins, their role is not as specific as that of IgG (or IgY) in that their actions are more generic in protecting the gut epithelium. In addition, in many cases of over-heated (low-cost) dairy products, immunoglobulins may be destroyed, like any other protein.

Of course, bovine colostrum is a rich source of IgG (Figure 1). Indeed, there has been some evidence that providing such an ingredient to piglets may increase post-weaning growth performance. The real problem with bovine colostrum is its very expensive price (more than 30 euros per kg) relative to its required high inclusion rate (10-20 kg per metric ton of feed). In addition, there is usually a limited availability of bovine colostrum in the market, and what limited quantities exist are usually added into calf milk replacers.

Immunoglobulins from animal plasma

A rich and more potent source of immunoglobulins is of course that of animal plasma. This ingredient contains 8-25 percent immunoglobulins, and its presence in piglet feed at levels of around 30-70 kg/metric ton has been shown to dramatically increase piglet performance, especially during the first couple weeks post-weaning.

The original work to demonstrate the fact that animal plasma exerts its beneficial effect through its immunoglobulin concentration was pioneered at the University of Iowa (Figure 2). When plasma was fractioned into several component parts, only the fraction containing the immunoglobulins enhanced piglet performance comparable to whole plasma. This was verified later in many other studies by different research groups and has been well published in scientific journals (the latest is by Pierce et al., 2005). 

According to this paper: “...porcine and bovine plasma are beneficial to young pig performance during the first week after weaning and that the IgG fraction of plasma is the component that is responsible for the enhancement in growth rate and feed intake.”

Problems with animal plasma

Like most ingredients, however, animal plasma is not without its own problems. First, it must be pointed out that although animal plasma contains a relatively high level of immunoglobulins, these are “generic” immunoglobulins. This is due to the fact that animal plasma is derived from blood at the slaughterhouse. As such, its immunoglobulin concentration is hugely variable and, consequently, of extremely unpredictable composition.

As the potency of immunoglobulins depends on the actual health of the animals slaughtered and their exposure to different pathogens, it is entirely possible for one batch of plasma to contain 15 percent immunoglobulins and another as little as 8 percent, yet there is no guarantee the richer animal plasma will be more effective. As such, the level of immunoglobulins is entirely irrelevant, whereas their specificity to piglet pathogens is of paramount importance. Furthermore, many researchers and field nutritionists have expressed a concern regarding the safety of animal plasma, because it might be the carrier of pathogens itself, something that has created quite a stir, but is still unclear and rather overreaching.

In my opinion, we cannot deny the powerful position of animal plasma in modern piglet diets, but on the other hand, neither can we deny the fact that this ingredient is extremely expensive, exceeding at various times 4 euros per kg. Assuming a typical commercial prestarter diet with a ceiling of 600 euros per metric ton for ingredient cost, it is quickly evident that animal plasma added at the usual rate (5 percent) will require 200 euros or one-third of the total ingredient cost. This allows very little room for other specialty ingredients, and it is perhaps the reason why some modern formulas either contain very little plasma or very little in terms of lactose! Clearly, plasma is too expensive, perhaps because it is in such high demand from the pet food industry.

Immunoglobulins from eggs

Fortunately, a more sophisticated and less expensive source of immunoglobulins exists in the market, in the form of egg immunoglobulins. These are derived from eggs produced by hens hyper-immunized with specific piglet pathogens. As such, their eggs are extremely rich in immunoglobulins with a high specificity (both avidity and affinity) for piglet pathogens. Early research has demonstrated that piglets infected with various pathogens and then fed with egg immunoglobulins recover faster and with less loss of performance than unsupplemented piglets. More importantly, mortality due to disease is reduced drastically compared to the unsupplemented controls, with huge economical significance under practical conditions.

More recently, research and empirical evidence has provided compelling evidence that egg immunoglobulins are also effective in replacing animal plasma completely. In fact, many high-quality piglet formulas in Europe contain egg immunoglobulins instead of plasma, and this trend has intensified with the recent hike in ingredient prices.

Personal experiences with immunoglobulins

As a field nutritionist, I have always advocated the use of immunoglobulins in piglet diets. I basically started my career by using animal plasma to convert very expensive European-type diets (rich in expensive skim milk) into less expensive products by relying heavily on this ingredient as the driving force for feed intake. When an outbreak of hemolytic Escherichia coli epidemic was finally controlled only by the use of egg immunoglobulins (in diets that also contained animal plasma), I became interested in the role of immunoglobulins as a functional health component in piglet diets, using the egg immunoglobulins to enhance gut health in sensitive farms.

Much later, due to animal plasma being so expensive that it was nearly impossible to use, I was convinced by my own trial work that egg immunoglobulins could totally replace animal plasma. I switched gradually until I was able to retain plasma only where local market conditions required its presence, and that in limited amounts. In my own consulting practice, I have advocated the use of egg immunoglobulins based on my previous field experiences and those of my clients. In 2012, when I launched my own antibiotic- and zinc oxide-free piglet formulas, I elected egg immunoglobulins as the sole source of immunoglobulins. 

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