A process for determining a tissue composition characteristic of a live animal or carcass involves the steps of: (a) obtaining either or both of at least one infrared thermographic image of the animal while it is alive, taken from at least one view, or at least one image of the carcass of the animal after slaughter, taken from at least one view, each thermographic image being capable of being represented as an array of pixels providing temperature data representative of temperature information at the corresponding part of the image; (b) calculating the value of at least one statistical measure of the temperature data for each thermographic image; (c) providing a predictive model wherein the tissue composition characteristic is included as an output variable, and the statistical measures of temperature data for each thermographic image are included as input variables; and (d) solving the predictive model to provide the value of the tissue composition characteristic. The process of the invention is useful in a wide variety of homoeotherinic animals. Tissue composition characteristics of interest include, without limitation, lean body mass, grade, carcass yield and rib eye area. An apparatus for performing the processes of the invention includes: (a) image acquisition means for obtaining the infrared thermographic images; (b) computing and storage means for storing each image as an array of pixels, calculating the value of statistical measures of the temperature data for each thermographic image, and providing and solving the predictive model; and (c) output means for providing an output of the value of the tissue composition characteristic.