Representing tissue mass and morphology in mechanistic models of digestive function in ruminants

Representing changes in morphological and histological characteristics of epithelial tissue in the rumen and intestine and to evaluate their implications for absorption and tissue mass in models of digestive function requires a quantitative approach. The aim of the present study was to quantify tissue mass (M) and absorptive area (AA) from parameters that are easily derived from morphological inspection and histology of tissue biopsies, and to compare this representation with approaches in current model of digestive function. Relatively small changes of 5% in some morphological and histological characteristics were calculated to affect absorptive area (AA) and epithelial tissue mass (M) strongly in the rumen and the intestine of cattle. The cumulative effect of changes in volume, height and width of primary protrusions and of secondary protrusions of the rumen wall was 18% for rumen mucosal AA and 29% for rumen serosal AA. It was 24% for intestinal mucosal AA. The cumulative effect on rumen and intestinal M was 20% and 22%, respectively. The simulations indicate that allometric functions that relate volume or weight to AA and M require exponentiation with an exponent higher than those based on geometric shape or volume.