Effects of Canola oil-based high fat diets on growth, fat deposition and serum triglyceride and cholesterol levels in lines of mice selected for high and low fat percentage

This study was conducted to determine if there are biologically important interactions of: genotypes of mice, differing in polygenically controlled body fat percentage, with levels of dietary fat from Canola oil which is rich in monounsaturated fat and low in saturated fat. Four levels of fat (12.5, 25, 37.5 and 50% of dietary energy) were provided nd libitum from four to seven, or four to 10 weeks of age to three lines of mice (HF, high body fat content; LF, low body fat content, and RC, random control with intermediate fat content). The lines were developed by directional selection for epididymal fat pad weight as a percentage of body weight (EFP%) which is highly correlated with body fat percentage. The HF line exceeded (P < 0.05) LF in weight gain, feed intake, feed efficiency, body weight, EFP% and serum cholesterol and triglyceride levels. Body water percentage, a measure of lean tissue percentage, and liver weight as a percentage of body weight were greater:(P < 0.05) in the LF line compared to HF. The 50% fat diet resulted in a reduction (P < 0.05) in energy intake, suggesting low palatability. Mice consuming 12.5, 25 and 37.5% fat did not differ in growth rate (P > 0.05), but feed efficiency at 25 and 37.5% was greater (P < 0.05) than at 12.5% since feed intake on a weight basis was reduced. There were no important biological effects of diet on EFP% or serum cholesterol level. At seven weeks of age serum triglyceride levels increased as dietary fat increased from 12.5 to 37.5% fat, but no clear trend was apparent. However, the LF line displayed a resistance to change in triglyceride levels as fat level increased. In general, while statistically significant genotype by dietary level interactions were detected for some traits, there were no biologically important interactions since the ranking of lines was not affected when compared across different levels of fat. The effects of dietary monounsaturated fat levels were generally smaller than the genetic line differences established by selection for high and low body fat percentage.