Efficacy of the Calcium Salt and Free Acid Forms of Methionine Hydroxy Analog for Chicks

Abstract

Four chick assays were conducted to assess the efficacy of commercially available DL-2-hydroxy-4-methylthiobutyrate in both the calcium salt (OH-M) and free-acid (OH-MFA) forms and a freeze-dried preparation of OH-methionine free acid polymers (OH-MFAP) relative to DL-methionine (DL-M). Young male New Hampshire × Columbian chicks were fed chemically-defined diets devoid of sulfur amino acid (SAA), or methionine-deficient semipurified feather meal diets supplemented with graded levels of DL-M to produce a linear growth response, or OH-M, OH-MFA, or OH-MFAP at a level isosulfurous to the highest addition of DL-M. The slope-ratio procedure was used to estimate the molar efficacies of OH-M, OH-MFA, and OH-MFAP relative to DL-M. Comparative toxicities of these compounds were also determined.OH-M, OH-MFA, and OH-MFAP were inferior to DL-M when fed as the sole source of SAA in a chemically-defined diet. Molar efficacies of OH-M and OH-MFA relative to DL-M were 87% and 78%, respectively. The OH-MFAP had an efficacy value of 69%, an indication that the trimers and higher-order polymers may not possess full M activity. All OH-methionine compounds were inferior to DL-M as sources of supplemental M in the feather meal diet. Molar efficacies of OH-M and OH-MFA were 84% and 77%, respectively. Again, OH-MFAP was inferior t o DL-M, OH-M, and OH-MFA. Thus, OH-MFAP had an efficacy of only 54%. The distinct superiority of DL-M over OH-M and OH-MFA in the feather meal diet was unexpected, but it may be explained by the diet's extreme deficiency of M coupled with an excess of cystine.Toxicity, as judged by magnitude of growth depression and severity of hemolytic anemia together with splenic hemosiderosis, was lower for the M analogs than for DL-M.