The role of dietary protein source in the development of cholesterol metabolism in rabbits

Twenty-one male 4-week-old New Zealand white rabbits were assigned to one of three dietary treatments (seven rabbits/treatment) in which protein source was derived from varying casein to whey ratios (100:0, 80:20, 40:60). Blood was collected at 10, 14, 18, and 20 weeks and animals were killed at 24 weeks and blood, livers, and aortas were removed. From weeks 20 to 24, a 0.4% cholesterol diet was fed. Results showed that animals fed the 40:60 diet had highest blood cholesterol concentrations prior to the cholesterol challenge (P < 0.05). After the challenge, differences disappeared. Low density lipoprotein and high density lipoprotein cholesterol concentrations in 40:60 animals were also higher than in 80:20 animals until 20 weeks of age (P < 0.05). Total triglycerides were highest in 100:0 fed animals at 10 and 14 weeks of age (P < 0.05) and stayed highest in this group after the challenge (P < 0.05). Rabbits fed 40:60 diet had higher 3-hydroxy-3-methylglutaryl coenzyme. A reductase activities than the 100:0 rabbits (P < 0.05). Total liver lipids were also higher in the 40:60 than 100:0 group (P < 0.01), and fecal cholesterol content was higher in the 80:20 than 100:0 group (P < 0.05). Bile acid excretion and atherosclerotic plaque formation were not affected by dietary treatment. These results indicate that plasma lipids are influenced by dietary protein source during the postweanling period, but the mechanism for this response remains to be defined.