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 import ant interactions of: genotypes of mice, differing in polygenically con trolled body fat percentage, with levels of dietary fat from Canola oi l 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 li nes of mice (HF, high body fat content; LF, low body fat content, and RC, random control with intermediate fat content). The lines were deve loped by directional selection for epididymal fat pad weight as a perc entage of body weight (EFP%) which is highly correlated with body fat percentage. The HF line exceeded (P < 0.05) LF in weight gain, feed in take, feed efficiency, body weight, EFP% and serum cholesterol and tri glyceride levels. Body water percentage, a measure of lean tissue perc entage, 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) t han at 12.5% since feed intake on a weight basis was reduced. There we re no important biological effects of diet on EFP% or serum cholestero l 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 a pparent. However, the LF line displayed a resistance to change in trig lyceride levels as fat level increased. In general, while statisticall y 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 l evels of fat. The effects of dietary monounsaturated fat levels were g enerally smaller than the genetic line differences established by sele ction for high and low body fat percentage.