An Evaluation of Methionine Hydroxy Analog Free Acid Using A Nonlinear (Exponential) Bioassay

Two experiments were conducted to determine the bioefficacy of methionine hydroxy analog free acid (MHA-FA) using the nonlinear (exponential) bioassay method. Male broiler chicks were fed a low methionine diet composed primarily of ground yellow corn and soybean meal for the 1st wk. The experimental diets, which varied in eight levels of DL-methionine and in eight equimolar levels of MHA-FA, were fed from 7 to 21 days of age. The source of protein was soybean meal and isolated soybean meal (15% of each) in the first experiment and soybean meal and peanut meal (23 and 21%, respectively) in the second experiment with glucose as the primary source of energy. Compared with DL-methionine on an equimolar basis, the bioefficacy of the MHA-FA was 72 ± 5 and 73 ± 7% using weight gains and feed conversions, respectively, from the first experiment and 85 ± 11 and 79 ± 8% using weight gain and feed conversion from the second experiment. These results clearly show that DL-methionine is much superior to MHA-FA on an equimolar basis.