Comparison of organic and inorganic zinc sources to maximize growth and meet the zinc needs of the nursery pig.

Zinc is the trace element involved in more biological functions than any other micromineral in the nutrition of the newly weaned pig. Its role in growth via protein synthesis and antioxidant defense makes it a key nutrient in the diet of the newly weaned nursery pig for maximum lean tissue growth and health. In this study, 500 pigs (5 pigs/pen) were weaned at approximately 18 d of age and fed 0, 25, 50, 75, or 100 mg/kg of Zn supplied as organic or inorganic Zn or 50 mg Zn/kg combination with 50% Zn from each source. Pigs were killed at 0, 10, and 35 d of the study to determine mineral tissue concentrations and antioxidant activity in the liver and the amount of metallothionein (MT) protein in the liver, duodenum, and jejunum. Growth performance did not differ for the pigs supplemented with Zn but were greater than those fed the basal diet with no added Zn (P ≤ 0.05). Hepatic Zn concentration was numerically maximized with 75 mg/kg of organic Zn, but 100 mg/kg of Zn of inorganic Zn was necessary to achieve a similar concentration. At d 10, Mn superoxide dismutase in pigs fed no supplemental Zn was lower than when pigs were fed organic Zn (P ≤ 0.05). Hepatic MT responded in a linear manner with organic Zn (P ≤ 0.01) and pigs fed the basal diet had less than those supplemented with Zn (P ≤ 0.01). Duodenal MT was greater at d 10 with organic Zn (P ≤ 0.01) than pigs fed the basal diet, and at d 35, there was a linear response to both organic and inorganic Zn (P ≤ 0.01). As expected, jejunal MT was reduced compared to this protein in the duodenum. The provision of Zn at 50 mg/kg from either source resulted in greater jejunal MT than when Zn was fed as a combination of both sources at the same concentration (P ≤ 0.05). Our data indicate that the needs of the nursery pig, that is, Zn requirements for health and well-being, have changed since the data used to establish the 2012 Nutrient Requirements of Swine (NRC, 2012) was published. Organic minerals are shown in this study to be managed biologically in a different manner than inorganic Zn (sulfate) in the young pig. The newly weaned pig, while changing nutritional sources and physical environments, has extremely high biological demand for antioxidant defense. Our data show that to maximize growth, health, and well-being, 75 mg/kg of organic Zn in a complex nursery diet benefits today's fast growing pigs with a very high lean tissue composition.