Comparative effects of dietary protein and cholesterol-fat content on genetically lean and obese pigs

Interactions of a high fat-high cholesterol diet with low and high dietary protein levels were tested in genetically obese and lean growing pigs. Sixty-four growing swine (32 obese and 32 lean) were utilized in a 9-wk experiment in which four diets were fed in a 2 X 2 factorial arrangement with two levels of plant protein (8 and 16%) and two levels of fat and cholesterol (0 added or 11% beef tallow-3% dried egg yolk added). Daily gain and gain-to-feed ratio were significantly reduced by low protein (P less than 0.01) and increased by high fat-high cholesterol. Obese pigs gained weight faster than lean pigs but were less efficient in feed utilization (P less than 0.02) except when consuming low protein diets (P less than 0.001). Plasma cholesterol was increased by low protein (P less than 0.01) and by high fat-high cholesterol (P less than 0.02); highest values were in pigs fed low protein-high fat-high cholesterol. Lean pigs showed a greater rise than obese pigs in plasma cholesterol when fed low protein diets, reflecting a higher dietary protein requirement for lean pigs as indicated by plasma total protein, albumin and urea nitrogen (urea-N) responses to diet. Percentage of aortic surface area stained by Sudan IV tended to be higher in lean than in obese pigs but the difference was not statistically significant (P less than 0.25). The data show the hypercholesterolemic effect of dietary protein restriction in growing swine and establish that genetic differences related to body composition and quantitative protein requirement affect the response.