Use of a four-parameter logistic model to evaluate the protein quality of mixtures of Mormon cricket meal and corn gluten meal in rats.

Weanling Sprague-Dawley rats were fed diets containing corn gluten meal (CGM), Mormon cricket meal (MCM), MCM supplemented with methionine (MCM + Met) or CGM-MCM mixtures as the sole source of dietary protein in purified diets. Animal response (weight or nitrogen gain) was analyzed as a function of nitrogen intake and described by a series of curves using a four-parameter logistic model. Parameter sharing was used to differentiate statistically between the response curves. When used for maximum nitrogen retention the quality of the protein sources could be ranked as follows: MCM + Met greater than 40 CGM-60 MCM greater than 50 CGM-50 MCM greater than 60 CGM-40 MCM greater than MCM greater than CGM. When used for maximum weight gain the ranking was as follows: MCM + Met greater than 40 CGM-60 MCM greater than 50 CGM-50 MCM greater than 60 CGM-40 MCM greater than MCM greater than CGM. The rankings of the protein sources when used for weight maintenance or nitrogen equilibrium were similar to those seen for maximum weight or nitrogen gain except for the ranking of MCM, which changed from fifth to first. These results show MCM to be a good quality protein source and that methionine is the first limiting amino acid when used for growth but not for maintenance. The shape of the response curves was dependent upon the response criteria as well as the source of dietary protein. The factors that may affect the shape of the dose-response curves and the application of nonlinear models toward animal feeding programs are discussed.