Overview of Iron Toxicity in Newborn Pigs
Reports of toxicity after SC or IM injection of iron preparations in newborn piglets are sporadic, and the risk is not high; however, toxicity does occur occasionally. In some litters, death occurs quickly, from 30 min to 6 hr after injection; in others, death is delayed for 2–4 days. (Also see Nonregenerative Anemias in Animals.)
Toxicity may be seen in three forms. In the first form, damage to the muscles around the injection site causes potassium, among other substances, to be released; the blood potassium level rises and interferes with cardiac function. Usually, the whole litter is affected. Piglets may appear anemic, become weak, cannot stand, and have muscle tremors followed by convulsions. Respiratory distress may be seen. There is swelling at the injection site. On necropsy, skin and muscles may appear pale, and there is edema and a brownish black discoloration at the injection site. Waxy degeneration of skeletal and heart muscle may be seen; there may be hemorrhages in the heart and necrosis of the liver and kidneys.
In the second, less acute form of toxicity, the excess iron appears to block the body’s defense mechanisms by overwhelming the phagocytic cells, which increases the likelihood of infection. Death occurs in ~2–4 days. In young piglets, the most likely infection is an Escherichia coli enteritis and, although some of the changes seen in the first form may be seen at necropsy, they are less obvious, and the enteritis contributes markedly to death.
The most important precipitating factor of iron toxicosis in pigs is a low vitamin E or selenium status of the sow. If either nutrient is low in the sow, pigs will either be born deficient in vitamin E or selenium or the colostrum will not be able to provide adequate amounts of these nutrients to meet the antioxidant needs of nursing piglets. Supplementing the sow’s diet with 50 IU of vitamin E/kg and 0.15 mg of selenium/kg will improve the status of the sow and prevent iron toxicity in the piglets. Injections of vitamin E/selenium during late gestation may also help prevent iron toxicity in piglets.
A third, more rare form of toxicity is associated with calciphylaxis, the massive mobilization of calcium after injection of iron preparations, both in the presence and absence of supplementary vitamin D. It occurs within several days of iron injection and is associated with development of hard swellings at injection sites. Death may occur, and calcification in other parts of the body may be seen at necropsy.