The most important components of a swine herd health management program appear to be all-in/all-out pig flow, segregated weaning, vaccinations, biosecurity and sanitation. However, these powerful tools are often inadequate and other tools are needed. Antibiotics are also important for protecting pig health, whether delivered through the feed or other routes, but legitimate concerns about antibiotic resistance are bringing pressure on the pig industry to reduce their use.
There is another set of potentially powerful health technologies associated with the feed. Most of these are special feed ingredients or feed additives, although some relate to formulations or feeding methods. Several of the feed technologies suggested to improve pig health are listed in Table 1. Some of these technologies, such as probioticsand low-protein diets,are believed to have direct effects on microbial populations in the digestive tract which result in improved pig health. Others, such as yeast-based mannans and spray-dried plasma, alter immune function. Two examples of these technologies, low-protein diets and yeast-based mannans, are highlighted in this paper.
There is no reason to believe that all of these technologies are equally effective, or even that they are all effective at all. Some have not been adequately tested. Responses to some appear to be inconsistent or weak, based on the data currently available. On the other hand some are clearly beneficial, as shown by the following discussion.
Table 1. An incomplete list of potential dietary technologies to improve pig health and productive performance
When the digesta in the lower gut contains a high concentration of nitrogenous compounds, that encourages the proliferation of undesirable bacteria such as Clostridia. Fermentation of the nitrogenous compounds by these bacteria produces various end-products that are potentially detrimental to the host; p-cresol and putrescine are two examples. High concentrations of nitrogenous compounds in the digesta of the lower gut may be caused by a diet with a high protein concentration and/or poorly-digestible protein. Thus, lowering the dietary protein level may be expected to reduce the production of the detrimental end-products and improve gut health.
Several studies confirm the benefit of low-protein diets on the health of young weaned pigs. Care must be taken to maintain relatively high amino acid levels in the diet when the crude protein level is reduced, to avoid sharp reductions in growth performance. It is often beneficial to lower protein levels even if that reduces performance slightly for a short time, as the pigs can often compensate by faster growth later.
The pig's immune system is vital, as its proper functioning protects the pig from disease and death. When the immune system is stimulated, it triggers a cascade of protective mechanisms including production of acute-phase proteins in the liver and pro-inflammatory cytokines in many tissues,activation of protective immune cells, fever, inhibition of appetite, and eventually production of protective antibodies. The immediate response is called inflammation and contributes to the animal's ability to fight off infection. Unfortunately, inflammation also reduces growth. The inhibition of appetite reduces feed intake, limiting the pig's nutrient supply and therefore its growth. Production of acute-phase proteins, cytokines and immune cells takes amino acids and energy that are then not available to support growth.
The ideal situation when a disease challenge arises would be a vigorous immune response, but then a prompt reversion to normal growth as soon as the danger has passed. Unfortunately, the inflammation often continues for a prolonged period. Livestock immunologists now believe that reducing inflammation would improve growth performance of pigs amid the challenges of commercial pig production. We and others have shown that several feed ingredients or additives can do just that, as shown by the examples below.
Research in this area has been facilitated by use of the endotoxin lipopolysaccharide (LPS), a component of some bacteria, which causes a strong inflammatory response.
Two prominent examples of yeast-based mannan products are Bio-Mos and Actigen. Our research shows that both of these products affect the immune system.
Several years ago we analyzed the known data on the effect of Bio-Mos on growth performance of young pigs. The results showed faster growth and better feed efficiency of pigs fed MOS than of the controls. The response was larger where pigs grew more slowly. The addition of MOS was most effective immediately after weaning, but a smaller response may persist for several weeks. Our recent data provide a potential explanation for how Bio-Mos improves performance.
There is now considerable evidence that Actigen also improves growth performance, perhaps through similar mechanisms.
An in vitro study from our lab suggested that Bio-Mos may have direct effects on immune cells collected from pig lungs. Adding Bio-Mos to the cells in culture caused them to produce more of the pro-inflammatory cytokine TNF-α. However, when cells were stimulated by LPS to produce a high level of TNF-α, adding Bio-Mos reduced the production of this cytokine. This pattern of response suggests that Bio-Mos may provide protection by stimulating the immune system, but may also protect against costly excessive and prolonged inflammation. Other types of data support this desirable pattern of response. For example in pigs challenged with the porcine reproductive and respiratory syndrome (PRRS) virus, feeding Bio-Mos increased leukocyte populations and antibody titers, providing stronger protection against disease. It also reduced the serum concentrations of proinflammatory cytokines, and increased anti-inflammatory cytokines, changes that likely lead to improved growth performance. One notable overall clinical effect of Bio-Mos was to shorten the duration of the fever caused by the PRRS infection, which is consistent with reduced inflammation. Gene expression data also support the pattern, as the expression of several genes important in the immune response were increased by Bio-Mos in unchallenged pigs but decreased in challenged pigs.
In a parallel PRRS-challenge experiment, Actigen also increased leukocyte populations and antibody titers, suggesting that it also enhances protection against disease. It improved feed efficiency of pigs challenged with PRRS. A controlled experiment on a commercial farm appeared to support the protective effects of Actigen, showing a tendency to reduced mortality of pigs fed the product.
Feed-based technologies can be important in managing pig health. Several such technologies have been suggested. Benefits of low-protein diets, of Bio-Mos and of Actigen are described here.
This paper was presented at the XI National Congress of Swine Production (CNPP), Salta, Argentina, August 14-17, 2012.