Serum lipidomics analysis reveals yolk sac absorption differences in newly hatched chicks

The yolk sac provides nutrients to a newly hatched chick with maternal nutrient substances including large amounts of lipids. Higher resorption of the yolk sac is generally considered positive for chick development. However, it is hard to determine yolk sac absorption differences among living chicks with similar body weight for assessing chick quality. In this study, we explored the serum lipidome changes using a lipidomics strategy to elucidate the underlying mechanisms of yolk sac absorption difference in day-old chicks and determine some effective indicators for chick quality evaluation. A total of 588 hatching eggs were collected from a breeder flock and classified into 7 weight categories (56-70 g, with 2 grams in each category). After hatching, the chicks were grouped into 12 groups based on sex (male or female) and body weight (≤39 g, 39-41 g, 41-43 g, 43-45 g, 45-47 g, >47 g). The quality of the chicks and yolk sac index were assessed. Then, 12 male chicks from 45 to 47 g and 12 female chicks from 39 to 41 g were sacrificed to perform serum lipidome detection using liquid chromatography-mass spectrometry (LC-MS). The results showed that the yolk sac index was significantly positively correlated with body weight in both male and female day-old chicks (P < 0.01). The yolk sac index did not affect the concentration of glucose, triglycerides, or cholesterol in the serum (P > 0.05). A total of 1271 lipid species across 40 subclasses were identified in the serum. 221 lipids in male birds and 284 lipids in female birds with yolk sac index variation were significantly different (P < 0.05). As the yolk sac index increased, the serum levels of triglyceride, sphingomyelin, phosphatidylcholine ether bond, lysophosphatidylcholine, and lysophosphatidylethanolamine decreased in male birds, while those of triglyceride, ceramide-NS, and phosphatidylcholine increased in female birds. Phosphatidylglycerol (PG) (18:1_18:1), PG (18:0_18:2) and glycosphingolipid Hex2Cer (d18:1/18:0) contents were significantly downregulated in both male and female birds, which could serve as candidate biomarkers for yolk sac absorption, pending further validation in larger cohorts. Overall, the findings provide a novel understanding of yolk sac absorption and utilization in newly hatched chicks.