Effect of genotype on whole-body and intestinal metabolic response to monensin in mice

Two lines of mice, M16 selected for rapid growth and a randomly,elected control ICR as well as their reciprocal crosses were used to stud), the effects of genotype on whole-body energetics and intestinal responses to monensin. Six mice, eight weeks of age, from each line or reciprocal cross were assigned to one of two treatments, 1) drinking water containing 20 mol/l. monensin dissolved in 0.5% V/V ethanol, and 2) drinking water containing 0.5% V/V ethanol (control) for two weeks, After 11 days (age of 9 weeks and 4 days), whole-body O-2 consumption was measured. At the end of two weeks. jejunal O-2 consumption. intestinal tissue composition and histomorphometrics as well as the rate and efficiency of glucose absorption were estimated. In comparison with the control, monensin administration in drinking water resulted in less daily water intake (13.4 vs. 15.5 ml/mouse, p 0.05) effect on whole-body O-2 consumption and jejunal function, whilst selection for rapid growth resulted in an apparent down-regulation of intestinal function. These data suggest that genetic selection for increased growth does not result in concomitant changes in intestinal function. This asynchrony in the selection for production traits and intestinal function may hinder full phenotypic expression of genotypic growth potential