A non-therapeutic method of enhancing the growth of an animal, the method comprising causing the animal to ingest or absorb an effective amount of one or more Fe III complex compounds of Formula I: Fe x (ligand) y Formula I wherein x is an integer value of 1-2, y is an integer value of 1-3, and each ligand present is independently a conjugate base of an α-hydroxy acid selected from the group consisting of citric acid, tartaric acid, lactic acid, glycolic acid, isoleucic acid, malic acid, and mandelic acid; or each ligand is a conjugate base of an amino acid independently selected from the group consisting of glycine, alanine, aspartic acid, cysteine, glutamic acid, isoleucine, leucine, methionine, phenylalanine, proline, serine, threonine, and valine; and salts and/or hydrates thereof, wherein growth of the animal is enhanced compared to an untreated control, wherein the enhanced growth is based on measurements of one or more characteristics selected from the group consisting of body weight, average body weight, feed intake or average feed intake, weight gain or average weight gain, and mortality adjusted feed conversion ratio (MFCR), and wherein the animal is a mammal or bird, and wherein, when the animal is poultry, then: (a) the animal is caused to ingest or absorb an effective amount of the one or more Fe III complex compounds in the form of a composition that consists essentially of the one or more Fe III complex compounds and a poultry feed, or in the form of an animal drinking water that consists essentially of the one or more Fe III complex compounds and water; and/or (b) the animal is caused to ingest or absorb an effective amount of the one or more Fe III complex compounds in the form of a composition that does not include an antibiotic as an additive. x is an integer value of 1-2, y is an integer value of 1-3, and each ligand present is independently a conjugate base of an α-hydroxy acid selected from the group consisting of citric acid, tartaric acid, lactic acid, glycolic acid, isoleucic acid, malic acid, and mandelic acid; or each ligand is a conjugate base of an amino acid independently selected from the group consisting of glycine, alanine, aspartic acid, cysteine, glutamic acid, isoleucine, leucine, methionine, phenylalanine, proline, serine, threonine, and valine; and salts and/or hydrates thereof, wherein growth of the animal is enhanced compared to an untreated control, wherein the enhanced growth is based on measurements of one or more characteristics selected from the group consisting of body weight, average body weight, feed intake or average feed intake, weight gain or average weight gain, and mortality adjusted feed conversion ratio (MFCR), and wherein the animal is a mammal or bird, and wherein, when the animal is poultry, then: (a) the animal is caused to ingest or absorb an effective amount of the one or more Fe III complex compounds in the form of a composition that consists essentially of the one or more Fe III complex compounds and a poultry feed, or in the form of an animal drinking water that consists essentially of the one or more Fe III complex compounds and water; and/or (b) the animal is caused to ingest or absorb an effective amount of the one or more Fe III complex compounds in the form of a composition that does not include an antibiotic as an additive. (a) the animal is caused to ingest or absorb an effective amount of the one or more Fe III complex compounds in the form of a composition that consists essentially of the one or more Fe III complex compounds and a poultry feed, or in the form of an animal drinking water that consists essentially of the one or more Fe III complex compounds and water; and/or (b) the animal is caused to ingest or absorb an effective amount of the one or more Fe III complex compounds in the form of a composition that does not include an antibiotic as an additive.