Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

John A. Hebert, Jr


Several experiments were conducted to evaluate the influence of various lipids on laying hen cholesterol metabolism. Hens of equal age and production status were used and housed in individual cages with individual feeders. Main responses measured were yolk, liver and serum cholesterol, and fatty acid composition of serum cholesterol esters. Preliminary results showed a significant linear yolk cholesterol increase on day 9 with 0, 0.5, and 1% dietary cholesterol. Added levels of up to 4% cholesterol for 21 days failed to significantly increase further yolk cholesterol. Serum cholesterol was unaffected. In six subsequent experiments, the following lipid comparisons were made with or without 1% dietary cholesterol; one, hydrogenated coconut oil (HCO), lard and tallow; two, HCO, safflower oil (SO) and olive oil (OO); three, coconut oil (CO), OO and SO; four and five, SO + OO and OO + TO respectively at 8-0, 6-2, 4-4, 2-6 and 0-8% combinations; six, tripalmitin (TP) and TO at 0 and 9% levels. The lipids themselves did not affect most variables measured. Dietary cholesterol significantly increased yolk and liver cholesterol with all lipids used. With cholesterol, HCO versus OO and SO, and TP versus TO promoted significantly higher yolk cholesterol. Likewise, liver cholesterol was increased by TP but the opposite was true with HCO or SO as compared to OO, lard and tallow. Increasing TO in the OO-TO mixture depressed liver cholesterol. Cholesterol significantly increased serum cholesterol (total, ester, free) and most esters particularly cholesterol oleate (C18:1) but ester/free ratios were unaffected. With cholesterol, OO promoted higher serum cholesterol, cholesterol myristate, palmitate, palmitoleate steareate, oleate, and linoleate (C18:2) then HCO or SO. Likewise effects were seen with higher TO to OO ratios especially on C18:1. HCO promoted more C18:1 than SO. TO diets significantly increased serum cholesterol ester, C18:1 and C18:1/C18:2 ratios above the TO or triglyceride-free diets in presence of cholesterol. Similarly, OO increased C18:1/C18:2 ratios and TO enhanced them as compared to SO. Cholesterol increased bile volume and seemed to increase and decrease liver and yolk weights respectively. Lower cholesterol absorption was observed with HCO, CO, and TP. Feed intake and egg production were unaffected.