Fine-tuning zinc nutrition for sows

By Lee Johnston, Professer of Swine Nutrition and Management

October 2018

Just like humans, pigs have daily dietery needs such as water, energy, protein (more specifically amino acids), vitamins, and minerals. As a percentage, vitamins and minerals are required in very small amounts but they play a very important role in ensuring pigs maintain healthy, productive lives. Zinc is one mineral that is required in the diet of pigs. Zinc is called a “trace” mineral because it is required in trace amounts (think parts per million). To provide some perspective on the size of a part per million, one part per million is like traveling one inch on a 16 mile journey. Typically, pigs require dietary zinc at 50 to 100 parts per million. Even though zinc is required in very small amounts, it plays important roles in development of reproductive organs, wound healing, tissue repair, skin integrity, bone development, soundness of the skeleton, and other bodily functions. 

The dietary requirements for zinc in swine diets were established using pigs in the 1950’s and 1960’s with little recent research conducted on modern, highly productive pigs. Since the 1960’s, sows have increased productivity from about 8 pigs per litter to modern levels of 14 or more pigs per litter. This increased productivity presumably would increase the sow’s zinc requirement, but this idea has not be tested thoroughly. Furthermore, the efficiency with which pigs extract zinc from dietary sources, called digestibility, has been studied more completely in growing pigs than in breeding sows. Some sources of zinc are more easily digested by growing pigs than others but these differences have not been evaluated in sows. 

Pork producers and feed industry nutritionists need to formulate diets regularly and feed sows on farms daily. In the absence of up-to-date information on zinc requirements and zinc digestibility of feed ingredients, nutritionists use the old information and add an additional amount called a “safety margin”. Safety margins ensure that diets will not be deficient in zinc and will support optimal sow health and performance. However, the added zinc may not be needed by the sow. If the extra zinc is not needed, it will be excreted in feces which ultimately is spread on cropland. Consequently, outdated knowledge of zinc requirements and zinc digestibility of feeds may be contributing to undesirable loading of soil and the environment with zinc. 

Our swine nutrition group at the University of Minnesota with the financial support of QualiTech Corporation (Chaska, MN) is studying the digestibility of zinc in two zinc supplements commonly used in sow diets. One source is inorganic zinc sulfate and other is zinc complexed with a polysaccharide (SQM Zinc). The complexed zinc has been shown to be more easily digested by finishing pigs but digestibility of this complexed zinc has not been evaluated in sows. If we learn that the zinc in SQM Zinc truly is more highly digestible than the zinc in zinc sulfate, nutritionists can reduce supplementation levels in sow diets which will reduce excretion of zinc in feces and ultimately into the environment without compromising sow performance and health. 

This research advances the long standing practice of continually fine-tuning nutrition of pigs with the goal of improving pork production efficiency and reducing negative environmental effects of pork production. Read more about our swine nutrition studies.