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Feeding for immunity

By Elsje Pieterse, Charles Street Veterinary Consultants
Immunity protects the body against invading foreign bodies and is closely linked to the presence of antibodies. These antibodies recognise and bind specific corresponding disease agents and render them harmless.Over the past years a number of concerning issues have been noted in production units. These include an increase in the number of sows returning to service (even after pregnancy has been confirmed), increase in the number of abortions, increase in the proportion dead born piglets and an increase in pre-weaning mortality. In piglets the occurrence of PMWS and PDNS, mulberry heart disease, umbilical cord bleeding, death after iron injection and accumulation of fluid in the chest and abdominal area have been noted.
Many of these factors are influenced by the presence/or lack of certain immune activating agents and anti-oxidants.
Changes that occurred on farm level include improvement in housing, management and genetics. While a move away from therapeutics towards alternatives and vaccinations have also taken place. A major change was also seen in the way that animals are fed. The use of animal proteins has decreased substantially and producers have moved to the use of “corn soy” diets.
These changes are mainly due to legislation around the feeding of mammalian protein, the poor quality of avian protein and the high cost of marine protein. There has also been an increase in fat levels of diets while fibre content tended to decrease in many instances. Non-medicinal feed additives found their way into feeds and these included organic acids, enzymes, anti-oxidants, pre- and pro-biotics and neutraceuticals.
On the vitamin and mineral premix side the packs were combined in such a manner as to replace multiple packs with single packs and methods have been devised to protect certain vitamins from oxidation.
Nutritional factors that must be kept in mind is the role of certain vitamins and minerals in the immune systems. Vitamins are a chemically unrelated group of organic substances that must be ingested. Vitamins can be classed as fat- or water soluble. Fat soluble vitamins include Vit’s A,D,E and K of which Vit’s A,D and E have an influence on the factors discussed earlier.
Shortages of Vit A can lead to failure to fertilisation and resorption due to placental abnormalities. Vit D has an effect on the absorption of Calcium (Ca) and Phosphorous (P) and depres-ses the effect of phytate. Vit E is generally also known as the fertility vitamin and shortages can lead to the death of and resorption of fetuses. Vit E also serves as an anti-oxidant in preventing peroxidation and protection of Vit A.
Water soluble vitamins mainly include Vit C and the B Vitamins. The function of the B vitamins with relation to the immune system is mainly through acting as co-enzymes for metabolic pathways. Vit C plays a role in the mobilisation of Iron (Fe) and also plays a role in the formation of collagen (umbilical cord).
Minerals constitute the ash of the body and are classed as being macro or micro minerals. Macro minerals include Ca, P, Na, K, Cl and Mg while micro minerals include Fe, Cu, Mn, Zn, I, Co, Mo, F, As, Pb, Cu and Se. Macro minerals are mainly involved in skeletal, muscle and blood functions. They also act in energy transfer systems and play a vital role in maintaining water balance (NaCl – salt) and maintenance of gut pH (HCl — hydrochloric acid). Factors affecting the absorption of the macro minerals from the gut include gastric pH and the presence of phytate. Iron (Fe) is further dependant on the presence of a reducing agent (Vit C) and is negatively influenced by high fat diets.
Chief micro minerals directly affecting reproduction and immunity include Manganese (Mn),Zink (Zn), Iodine (I) and Selenium (Se). Shortages of these minerals generally lead to reproductive failure including delayed oestrus, foetal resorption, placental problems and sperm abnormalities. The absorption of these minerals, especially Zn, is greatly affected by the presence of phytate.
During pregnancy the sow mobilises nutrients to the conceptus. In high producing sows this mobilisation, of especially micro minerals, often represents more than what can be absorbed from the feed. This inability to absorb sufficient nutrients is linked to a number of factors. Amongst these factors is her physical ability to absorb inorganic minerals and anti-nutritional factors in the feed. The piglet once again obtains its ability to absorb these elements in utero meaning that it has to be exposed to these in the uterus in order for it to be able to absorb these after being born. As high producing sows can not absorb sufficient amounts it leads to a piglet being born with sub-optimal levels, suckling sub-optimal levels and not being able to absorb these substances from the feed as the ability was not developed in utero.
In the newly weaned piglet weaning shock due to the change in dietary and environmental factors should be considered. These changes have a detrimental effect on gut health and are associated with increased gastric pH and decreased digestibility and absorption of nutrients. These undigested nutrients flow to the lower digestive tract where it serves as nutrient source for microbes that in turn migrate up the tract where it causes digestive upsets or it forms toxins that can lead to metabolic disturbances and death.
The move toward soya bean products as main protein source in pig diets raise a number of issues. Soya contains sufficient proteins and a relatively good balance of amino acids and can therefore be the basis of pig diets. It does, however, also contain a number of anti nutrients including enzyme inhibitors (depresses protein digestion), haemaglutinin (clot promoting agent), goitrogens (depresses thyroid function) and phytate which is an active chelating agent binding to minerals in the gut and actively blocks the uptake of Ca, Mg, Cu, Fe, Zn and Se.
The move away for bran and fish also has an effect as the inclusion of fish leads to increased absorption of minerals. The fatty acid composition and especially the presence of q3 and q6 has a positive influence on the immune systems. It serves as an organic source of Ca and Zn and decreases the chelating properties of phytate. Bran is mainly used as a fibre source and negative effects are the decreased efficiency of feed utilisation, the mycotoxin threat and the presence of phytate while it serves as a source of organic minerals (Mg, Fe, Cu and Zn).
In weaners the main aim should be to look after the gut health of the piglet, thereby maximising digestion and absorption of nutrients. The identification and use of save fibre sources can be beneficial while the use of organic acids (pure/combinations/buffered), enzymes, pre- and pro-biotics and certain therapeutics can also be of value.
Methods to curb these negativities in sow diets include simple measures like the inclusion of animals proteins (fish meal) in sow diets, the inclusion of organic minerals in order to bypass the chelating effect of the phytate and to increase absorption from the gut while the addition of phytase, an enzyme that breaks down phytate, can also be added to the diet to reduce phytate levels.
Replacing approximately 30% of inorganic Se, Zn, Mn, and Cu with organic sources together with the inclusion of low levels of fish meal in dry sow diets have shown substantial benefit in terms of reproduction and piglet health.

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