Calculation of cholecalciferol transfer efficiency
The efficiency of vitamin D3 transfer in eggs as a function of dietary intake is expressed as cholecalciferol transfer efficiency
(Naber 1993; Walker and others 2012): transfer efficiency (%) =
100 × [yolk cholecalciferol concentration (IU/g) × yolk mass
(g) × egg production (% day−1 per hen)]/[feed cholecalciferol
concentration (IU/g) × feed intake (g/d per hen)]. The average
daily feed intake of 100 g/d per hen (weeks 3 to 40), the average egg mass of 53 g per egg (week 3 to 40), and the average egg yolk mass of 28% (or 15 g) of the egg (with shell) were used in the calculation of transfer efficiency. The determination of these production data is described in details in another report under preparation. The transfer efficiency at week 3 and its average value during weeks 3 to 40 for each enrichment level were obtained.
Egg yolk lipid analysis
The crude lipids of egg yolk were extracted by using the mod- ified Folch method (Christie and Han 2010). Briefly, 3 g of egg yolk was extracted twice with CHCl3 -MeOH (2 : 1, v/v). The liquid extract was washed with 0.74% KCl. The desolventized
egg yolk lipids were then dissolved in CHCl3 and stored at −26
◦C in the dark until analysis. The phospholipid composition of
egg yolk lipids was determined by 31 P NMR following a proce- dure described by Yao and Jung (2010). The yolk lipids (15 mg) were