There is not one golden solution that makes the use of antibiotic unnecessary, neither for disease treatment nor for preventive use or for growth promotion. All possible aspects around health care for pigs are at stake, like biosecurity, housing conditions, vaccination, breeding, and management around parturition, lactation and weaning. They all play a role in the prevention of clinical and subclinical disease. However, the role of a qualitative good feed should not be underestimated.
New born piglets have a very high energy requirement for activity and thermoregulation. They use three different sources of energy, namely their own glycogen deposits, colostrum and milk. Piglets are born with limited amounts of energy in glycogen depots in the liver and muscle tissues. The fat and lactose from colostrum must supply a sufficient amount of energy directly after birth. Thus colostrum intake is critical for survival and weight development. Piglets that have a lower birth weight, that are later in birth order, or that start late with suckling will consume less colostrum. So they are at risk for not taking in enough colostrum. Selection for large litters has increased the chance that some piglet in a litter will not get enough colostrum, because this genetic selection indirectly decreased birth weight and has increased the competition for milk between littermates; sometimes sows give birth to more piglets than they have tits.
Colostrum and milk are not only supplying energy, water and protein. They are an important source of immunoglobulins too. Unlike primates, pigs are dependent on the IgG absorbed in the intestines during the first two days after birth in order to obtain maternal antibodies. Therefore colostrum uptake during the first hours immediately after birth is crucial. Also during further suckling the immunoglobulins have an immune function. They can no longer be absorbed, but on the intestinal level they have a local immunological effect; the so called lactogenic immunity. In nature this lactogenic immunity is provided for at least 6 weeks, whereas under today's commercial circumstances pigs are weaned at 2, 3 or 4 weeks of age, so the lactogenic immunity stops at that moment, i.e. the direct protective effect of IgG is stopped at a moment where the immune system of the piglet is still immature. Other functional components in milk and colostrum are oligosaccharides, lactoferrins, and lactoperoxidase. These components have an influence on the gut health as well.
Piglet mortality is the highest during the first days after birth. An effective, although labor intensive method to increase the survival is to drench the lightest and weakest piglets in a litter during the first days after birth. To drench piglets they are lifted and the fluid is given in the mouth, where the piglets preferably swallow the fluid themselves. Drenching can be done with sugar solutions, milk replacer, and specific preparations. It has been questioned whether young piglets have to be drenched with a glucose solution instead of milk replacer. The experience is that some milk replacers may induce diarrhea in very young piglets. Whether milk replacers cause diarrhea in neonatal piglets depends on the kind of milk replacer. Well-designed non-plant-protein based milk replacers do not appear to have this negative effect. This relates to the source of protein and the digestibility of it. We have good experience at commercial farms with feeding milk replacer in combination with a plasma based colostrum supplement. (This supplement replenishes antibodies that piglets missed by not drinking sufficient colostrum). The number of weaned piglets increased with one piglet per litter. The high quality milk replacer that was used contained no plant protein and proteins in the formulation were chosen to regulates the time the milk stays in the stomach.
Immediately after weaning there are different things happening on the gut level that are strongly interrelated, namely anorexia, villus atrophy, reduction of digestive capacity and post-weaning diarrhea. A good diet can orchestrate this situation in a favorable direction.
Directly after weaning there is a period of transient villous atrophy and crypt hyperplasia. It takes time before piglets start eating after weaning. This post-weaning anorexia is the main etiological factor for damage to villi. Energy intake after weaning is positively related to villus height and intestinal integrity. During post-weaning anorexia crypt hypertrophy and local inﬂammatory responses are found. In the epithelial cell of the small intestine enzymes are present to digest disaccharides and (oligo-) peptides. When the villi become shorter the enzyme activity in the brush border is negatively affected. So this is an extra negative effect on carbohydrate and protein digestion. Moreover, even when there would be no anorexia related villus atrophy the digestive capacity has not yet reached its full capacity in the young piglet.
The major disease in weaned piglet is diarrhea, i.e. post-weaning diarrhea (PWD). An important cause of this diarrhea is the E. coli bacteria. Adhesion of E.coli results in the colonization of the intestinal tract. The pathogenic E.coli produce enteroxins(ETEC's). The enterotoxin production results in hypersecretion of water and electrolytes into the small intestinal lumen that exceeds the absorptive capacity of the colon. This process results in diarrhea, dehydration, reduced feed intake, reduced nutrient digestibility, reduced growth and even death. One of the most critical factors that affects the health of piglets experiencing PWD is the damage to the intestinal epithelium and hence weakened mucosal and cellular barrier functions. Lack of active immunity and damage to gut integrity generally increase adhesion of pathogenic bacteria to the mucosal layer. Therefore, a key factor for dietary interventions to minimize PWD is the ability of these diets to reduce the total number of pathogenic E. coli or to prevent adhesion of the ETEC to enterocytes, or a combination of both.
Another important cause of post weaning infections and post-weaning antibiotic treatments are infections caused by Streptococcus suis. Feed composition has an effect on the occurrence of S. suis related disease symptoms. Feed quality can prevent the piglet from becoming diseased or vulnerable for infection.
An appropriate pH value of the stomach is rarely maintained at weaning. This relates to diet changes and the physical incapacity of the young piglet to produce sufﬁcient HCl . Also high protein levels exert a buffering effect. The dietary electrolytes, calculated as the Base-excess or electrolyte balance, should be in balance . The acidiﬁcation in the stomach, which is the primary physiological defense mechanism to reduce the introduction of pathogens, should work to decrease the risk on PWD. The low pH is also important to have the right environment for pepsin to exert its digestive function. If protein is not digested fast enough it will reach the hind gut, where it can be fermented, as described above.
To promote health and to replace antibiotics there is a great interest in alternative feed additives, like organic acids, pro- and pre-biotics, and essential oils. Efforts have been made to find alternatives and to prove their functionality. A multitude of products is offered to the market. Nevertheless, a lot of understanding is lacking to make an educated choice for the right additive.
One step in finding alternatives for antibiotics in feed is understanding the mode of action of antibiotics. When antibiotics are used to treat intestinal infection it is clear that they help the host in overcoming infections by killing the infectious pathogen. For this purpose antibiotics are used at inhibitory concentrations. Antibiotics used as growth promotor mostly work at concentrations below inhibitory levels of pathogens. There is not a full understanding why antibiotics used as growth promotors exert their positive effect. At genus levels shift in the bacterial ecosystem are seen, as well as selection of resistance genes. But how and whether they really select for an beneficial microflora is not easy to understand. Niewold (2007) suggested that the function of antibiotic growth promotors is related to their direct influence on the immune systems of the host, by suppressing inflammation. When this hypothesis is true this requires alternative interventions that target this immune-modulation.
To find alternatives to steer intestinal health one prefers to understand how the intestinal ecosystem can be regulated. The intestinal ecosystem is a highly complex system that is kept in balance through multiple interactions between the host's immune system, the microbiota in the intestine, and the feed that is fed. On forehand it will be a challenge to shift the complex balance in a desired direction. Organic acids; especially in-vitro showing positive effects; but how is this effect in the buffered in-vivo system? The inconsistency in the reports of pro- and pre-biotic effects indicates the high degree of complexity in the development and application of probiotics. Essential oils have been extensively studied and used in a wide range of food systems to increase the safety and shelf life of foods. However, their impacts on growth performance of newly-weaned pigs have been inconsistent, even though changes in gut microbiota composition were observed .
The contribution Plasma proteins can have
In 2010 De Lange, Pluske et al. reviewed the possibilities to improve gut health and they wrote: "The addition of (spray-dried) plasma products to diets has revolutionized the feeding of newly-weaned pigs, and especially of pigs weaned before 18 days of age, in the last 15 years." More than any other animal protein porcine plasma protein is an excellent ingredient for piglet milk replacers and weanling diets. There is on the one side the amino acid profile and the excellent digestibility that make it an excellent protein source, but more important is that the functionality of the bio-active components in the blood product make it a superior ingredient. Studies have shown that porcine plasma performance better than milk proteins, hinting to the bio-functional components. Several studies have shown that plasma from porcine origin gives better performance than bovine plasma, suggesting species specific effects. There is a crucial role for immunoglobulins in plasma. The antibodies have a central role in the immune system and regulation. They capture pathogens, they opsonize them, they cause complement being released, they have a role in improving the integrity of epithelial layers, and so forth. Only in the first one or two days after birth they will be absorbed, later on they will have a local effect like the mother's milk has its lactogenic immunological effect. Spray drying of plasma protein is the preferred way of processing to guarantee all functionality is preserved in the dried powder.
The suckling and weaning phase in a piglet's life are a period where the smallest amounts of feed are consumed. It is also the phase where high mortality is seen and where the health of the pig needs support. Good quality milk and feed should be a part of the support strategy. Given the complexity one simple solution cannot be given. Nevertheless, it is evident that the emphasis in formulating milk supplements and starter diets has to be primarily on feeding the gut in the best way. The feed has to be attractive for the young piglet and the used proteins must be highly digestible, well tasting, not having adverse effects by themselves, and should be included at a limited – digestible - level. Plasma protein combines all these demands, for both milk replacers and starter diets, and has additional bio-functional properties.
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Article made possible through the contribution of Lourens Heres, Sonac and Ronald Mors, Morsvit Feed Consultancy