The relationship between yolk cholesterol and total lipid concentration throughout the first year of egg production in the domestic fowl.

1. Variation of egg yolk cholesterol and total lipid concentration (mg/g wet yolk) throughout the first year of egg production for the domestic fowl is described. 2. Yolk cholesterol concentration decreases between 20 and 30 weeks of age, and then remains constant until 70 weeks of age. Yolk total lipid concentration increases to a maximum at 40 weeks of age before decreasing to its original value at 60 and 70 weeks of age. 3. Bird means for yolk cholesterol and total lipid concentration are negatively related at 20 weeks of age, and essentially independent for the remainder of the first year of egg production. 4. Variation for yolk cholesterol concentration between 30 and 70 weeks of age appears to be a consequence of differences in the proportion of cholesterol to other lipid components. 5. Uptake of plasma lipoproteins characteristic of the immature bird is likely to be responsible for the high yolk cholesterol concentration at 20 weeks of age.