Modifying egg yolk cholesterol in the domestic fowl—a review

SummaryMuch controversy exists regarding the specific relationship between diet, plasma lipids and development of heart disease in humans. Irrespective of the controversy, there is growing public concern over dietary cholesterol consumption. There is also debate concerning the specific relationship between egg consumption and human plasma lipids causing much of the health profession to recommend a decrease in egg consumption regardless of an individual's propensity for coronary heart disease. This recommendation is due to the relatively high cholesterol content of the egg (200–300 mg). Currently, it appears that it would be economically advantageous for the egg producer to be able to market a low cholesterol egg. Many research efforts have been directed toward this goal. Numerous factors have been demonstrated to alter cholesterol deposition in the egg. Cholesterol content of egg yolk is increased by dietary cholesterol and fats. Dietary fiber and administration of certain drugs reduce yolk cholesterol concentrations but only marginally. Although selection studies have indicated sufficient genetic variability in yolk cholesterol to make a genetic selection program possible, selection for lower egg cholesterol has not been successful or has resulted in only modest (5–7 %) reductions in egg cholesterol levels with an associated decrease in egg production to perhaps maintain a minimum level of cholesterol in the egg. The inability to reduce markedly yolk cholesterol concentrations is possibly due to natural selection pressures to maintain a certain level of cholesterol in the egg for use by the developing embryo. Currently, therefore, there is little evidence to suggest that a commercially significant reduction in egg cholesterol content is going to occur by means of conventional nutritional manipulation or genetic selection programs. It appears that future efforts to modify yolk cholesterol levels should focus on the mechanism(s) responsible for monitoring/regulating cholesterol deposition in the egg and the potential for manipulating such mechanism(s) without invoking the cessation of lay associated with reducing yolk cholesterol through conventional means.