The fatty liver of newly-hatched pigeons is caused by an accumulation of sterol esters (STE) amounting to 620 mg/g total lipids of which 80% was sterol oleate. Triglycerides (TG) accounted for only 20 mg/g of total lipids. 2. After hatching, the relative amount of STE in the liver tissue decreased considerably while that of TG increased. The proportion of phospholipids (PHL) remained essentially constant. 3. The fatty acid composition of the liver lipids changed significantly, but specifically for each individual class during postnatal growth. Striking differences were the higher values of long-chain polyunsaturated acids (20: 4 omega 6 and 22: 6 omega 3) in PHL, TG and free fatty acids (FFA) and the higher proportion of oleic acid in the STE at hatching compared with those at older ages. 4. The predominant alterations in the relative composition of the liver lipids (lipid classes and fatty acids) occurred in the first week after hatching and may be accounted for by the decreasing yolk utilisation and adaptation to ingested food. The change within the diet itself from cropmilk to grain (starting around the 4th day) influenced the development of the lipid and fatty acid content only in a minor way. 5. The large weight decreased of the pigeon liver after the 19th day was accompanied by a decrease in absolute PHL content while TG stores were unaltered.
