University of Nebraska researchers compared the bioavailability of iron in two different sources of iron proteinate with that in feed-grade iron sulfate. Pigs which were iron deficient and anemic at weaning were given diets with no supplemental iron, nor supplements of iron sulfate or iron proteinate.

Weight gain and hemoglobin at the end of the three-week study increased as the iron supplementation increased. When hemoglobin repletion was compared, there were no significant differences between iron sulfate and either of the iron proteinate sources. The researchers concluded results indicate the iron in iron sulfate and the two iron proteinate sources were similar in bioavailability. Thus, price per unit of total iron should be the primary criterion when selecting among these iron sources.

Iron is a critical trace mineral for young pigs because the iron content of sows' milk is very low. Most newborn pigs are given an iron injection that meets their needs until weaning. After weaning, supplemental iron must be provided in the diet because the iron content of most ingredients is not adequate to meet the pigs' needs, especially during periods of rapid growth.

Iron sulfate is the most commonly used source of supplemental iron. The iron is in a form that is readily available to the animal (bioavailable) and it is relatively inexpensive.

However, other sources of iron are also marketed. Many of these sources are referred to as "organic" sources, because the iron is combined with an organic molecule such as an amino acid or protein. Organic sources are usually more expensive per unit of total iron than inorganic sources and therefore must offer some advantage if they are to be justified for inclusion in swine diets. If the iron in organic sources is more bioavailable than the iron in inorganic forms, this may justify their purchase and inclusion in swine diets.

Pigs selected for the experiments were given no supplemental iron (either oral or injectable) from birth until weaning at approximately 21 days post-farrowing. Blood hemoglobin concentrations were measured at weaning. Seventy-two barrows and 72 gilts were selected for each experiment based on hemoglobin concentration. The average initial weights were 11.6 and 11.1 lb. in experiments 1 and 2, respectively.

During the experimental periods, pigs were allotted to a basal diet or to diets that were formulated to contain 75 or 150 mg./kg. (ppm) of supplemental iron from feed-grade iron sulfate, or diets formulated to contain 50, 100 or 150 mg./kg. of supplemental iron from iron proteinate. The same source of iron sulfate was used in both experiments.

Pigs were allowed ad libitum access to feed and water throughout the three-week experimental period. Pigs were bled at the end of each week, and hemoglobin concentrations were determined. Hemoglobin repletion was calculated.

Pigs fed the diet without iron supplementation gained very little weight and their hemoglobin concentration declined as the experiment progressed. Addition of supplemental iron increased weight gain, feed intake, and feed efficiency linearly (P<.001) regardless of whether the supplemental iron was from iron sulfate or iron proteinate. The changes in growth performance per unit of supplemental iron were approximately equal.

Blood hemoglobin concentrations in the first experiment were also affected by iron intake. At the end of the experiment, (week 3) blood hemoglobin increased linearly (P<.001) as the supplemental iron concentration increased. The effects were particularly evident at the end of the experiment.

To calculate the relative bioavailabilities, hemoglobin repletion was related to supplemental iron intake. The increases in hemoglobin repletion were slightly greater for iron proteinate than for iron sulfate. Statistical analysis revealed the two sources were similar in iron bioavailability.

Results of the second experiment were very similar to Experiment 1. Both growth performance and blood hemoglobin concentration increased linearly (P<.001) as supplemental iron increased. The increase was somewhat lower for iron proteinate than for iron sulfate. As in Experiment 1, the value was not statistically different, indicating the two sources are similar in iron bioavailability. Researchers: Austin J. Lewis, Phillip S. Miller and Hsin-Yi Chen, Department of Animal Science, University of Nebraska, Lincoln, NE. Phone Lewis at: (402) 472-6423. L