6 modes of action can be distinguished in pigs.

Zinc and the gastro-intestinal tract

Zinc is associated with the maintenance or function gastrointestinal tract from taste buds of the tongue to the function of villus and crypt in the intestine. In intestinal tract, for instance, zinc helps maintain the stability of the intestinal microflora, to support a large diversity of coliforms in weaned piglets, and to reduce the susceptibility of pigs to E. coli infection. Further study has also reported that supplementation of pharmacological doses of zinc as zinc oxide act as an antimicrobial agent and improves the gastrointestinal tract function by increasing mucosal thickness, villi height, and width of the small intestine.

Zinc and enzyme activity

The enzyme copper/zinc superoxide dismutase (Cu/Zn SOD) has a vital role in normal body functions. In mammalian tissues, reactive oxygen species, such as superoxide radicals, hydroxyl radicals and hydrogen peroxide are continuously generated during aerobic metabolism. Excessive generation of reactive oxygen species can cause detrimental changes. Therefore these free radicals should be elemented from the body. Among the other enzymes that detoxify the free radicals, Cu/Zn SOD is one the most important enzyme that catalyses the elimination of free radicals.

Zinc and metabolic hormone activity

A normal thyroid status is dependent on the presence of many trace elements for both the synthesis and metabolism of thyroid hormones. The role of zinc in thyroid metabolism has been investigated in animals but with conflicting results. Recent findings in 2014 indicated a higher and lower, tri-iodothyronine and thyroxin concentration in zinc supplemented and zinc deficient pigs.

Zinc and growth

Dietary zinc enhances growth in livestock by activating the various enzyme systems that are essential for cell division and proliferation.

Zinc and pig reproduction

In case of male animals, zinc plays an important role in spermatogenesis. Reports have indicated that in zinc-deficient animals, Leydig cell development may be retarded and the response to luteinising hormone (LH) as well as testicular steroidogenesis reduced.

In sows, the control of zinc on oestrus behaviour, length of oestrus cycle and age at puberty is well described. However, zinc also plays a role in reproductive problems in animals – delayed puberty and lower conception rates, failure of implantation and reduction of litter size are also reported. Zinc has a significant role in repair and maintenance of uterine lining following parturition and early return of post-partum oestrus. Zinc deficient animals have been shown to have lower concentrations of follicle-stimulating hormone (FSH) and LH.

Zinc and the immune system

Zinc plays a very important role in controlling the immune system, and zinc-deficient animals experience increased susceptibility to a variety of pathogens. Zinc affects multiple aspects of the immune system, from the barrier of the skin to gene regulation within lymphocytes. Zinc is crucial for normal development and function of cells mediating non- specific immunity such as neutrophils and natural killer cells. Zinc deficiency also affects development of acquired immunity by preventing both the outgrowth and certain functions of T lymphocytes such as activation of Th1 cytokine production, and B lymphocytes.