The effect of egg yolk fatty acid composition on essential fatty acid utilization by the developing chick embryo was studied by feeding laying hens a fat-free diet supplemented with oils containing widely divergent contents of the essential n-6 and n-3 fatty acids. A control hen was fed a commercial feed for laying hens. The diets contained 20 to 4370 mg/100 g n-3 fatty acids and 360 to 8020 mg/100 g n-6 fatty acids. Fertile eggs were collected in pairs: one was incubated and the other served as an unincubated control. The fatty acid content of the unincu-bated egg and the newly hatched chick from each pair was compared. Some 50% of the total fatty acids in the egg yolk were incorporated into the tissues of the newly hatched chick. Regardless of diet, more yolk n-6 fatty acids were incorporated into the chick compared to saturated or monounsaturated fatty acids. The percentage of incorporation especially increased from the eggs containing relatively low amounts of n-6 fatty acids. The percentage of incorporation of n-3 fatty acids was similar to that of saturated and monounsaturated fatty acids when n-3 fatty acids were plentiful in the egg yolk, but increased significantly when n-3 fatty acids were low in the eggs. There was a generally linear relationship between essential fatty acids in the egg and in the chick, although levels of docosahexaenoic acid [DHA; 22:6(n-3)] in the brain did not respond proportionally. The developing chick preferentially removed DHA from the yolk, but did not synthesize more DHA when the amount of the DHA precursor, 18:3(n-3), in the yolk was increased. We concluded that the developing chick embryo requires 0.4-1.1% of egg energy as n-3 fatty acids and 4.8-6.2% as n-6 fatty acids, or a “dietary” ratio of n-6/n-3 of 5 to 14. This requirement may have relevance for humans as well.
ASJC Scopus subject areas
- Pediatrics, Perinatology, and Child Health