Lipid composition of pigeon cropmilk—I. Total lipids and lipid classes

1. Cropmilk of pigeons consists of cells loaded with fat. The composition of these lipids at different stages of the lactation period was determined by thin-layer and gas chromatographic procedures. 2. One day after hatching the lipids comprise 8.1% of the fresh weight of the cropmilk. They consist primarily of triglycerides (81.2%) and to a lesser extent of phospholipids (12.2%). Minor components are cholesterol, cholesteryl esters, free fatty acids, diglycerides and monoglycerides (each less than 2.5%). 3. After the first week of lactation the lipid content of the cropmilk drops gradually, due to a decrease of triglycerides. 4. Phosphatidyl choline, sphingomyelin and phosphatidyl ethanolamine are the major phospholipids of the cropmilk averaging respectively 52.8, 21.9 and 20.4% of the total phospholipids. Cardiolipin and phosphatidic acid, lysophosphatidyl choline and lysophosphatidyl ethanolamine are only present in trace amounts (each less than 2.5%).