J. King Saud Univ., Vol. 10, Agric. Sci. (1), pp. 33-41, Riyadh (A.H. 1418/1998)
The Relationships between Egg Yolk Cholesterol, Egg Production and Age of the Hen in Three Australian Layer Strains
T.M. Shafey*, J.G. Dingle **and M.W. McDonald**
* Department of Animal Production, College of Agriculture, King Saud University, Riyadh, Saudi Arabia
** Department of Animal Production, Gatton College, University of Queensland, Lawes, Queensland, Australia, 4343
Abstract. This paper reports the relationships between egg yolk cholesterol and egg weight, yolk weight, egg production and age of the hen in three strains of Australian commercial layers. Genotypes differed in egg weight, yolk weight, rate of lay, yolk cholesterol concentration (mg cholesterol/g yolk) and egg cholesterol content. Differences among strains were not significant when cholesterol was calculated as the concentration of the egg (mg cholesterol/g egg). Smaller eggs contained a significantly lower cholesterol content than larger eggs. The percentage increase in egg cholesterol content of large eggs was approximately equivalent to the percentage increase in their egg and yolk weights. Age of the hen was significantly positively correlated with yolk cholesterol concentration, egg cholesterol content and daily egg cholesterol output. Egg cholesterol content at 30 weeks of age was approximately 19% lower than that produced at 56 weeks of age whereas average egg weight was only 9% less at that age. It was concluded that differences in yolk cholesterol that occurred among strains of laying hens were mainly due to differences in responses in egg traits and not to responses in daily cholesterol output. A greater proportion of lower cholesterol eggs can be produced by choosing laying strains that are more highly productive at a younger age.