Replacement of Yolk of the Chicken Embryo in ovo with Fresh Yolk or Yolk Varying in Granule and Cholesterol Content

Abstract

A method has been devised to study the nutritional role of yolk cholesterol in the development of the chicken ( Gallus gallus domesticus) embryo using egg yolk replacement. Preliminary experiments revealed that 11 mL of yolk in medium-sized eggs were adequate to support embryos from 4 to 20 days of incubation, and that low levels of β-cyclodextrin (β-CD) and amyloglucosidase (AG) in yolk were tolerated by the embryo. Fresh egg yolk was treated with β-CD at 50 °C, centrifuged to remove the insoluble β-CD-cholesterol complex, and incubated with AG to degrade residual β-CD. The cholesterol content was reduced from 13.1 mg g−1 in fresh egg yolk to 1.3 mg g−1 in cholesterol-reduced yolk supernatant (CRYS). Yolk granules co-precipitated with the β-CD-cholesterol complex. The cholesterol concentration of CRYS supplemented with granules from fresh yolk ( i.e. CRYSg) was 3.2 mg g−1. When yolks of early 5-day embryos were replaced with 11 mL of CRYS, the maximum survival was 17 days of incubation. When yolks were replaced with 11 mL CRYSg, 30% of embryos survived to 20 days, a significant increase in survival compared to CRYS ( P < 0.05). Sixty per cent of embryos receiving fresh yolk (yolk controls) and 83% of embryos in intact eggs (intact controls) survived to 20 days. The controls did not differ significantly ( P > 0.05). Embryos in the CRYS and CRYSg groups had shorter survivals than yolk controls ( P < 0.001) and intact controls ( P < 0.005). These results suggest a methodological approach for investigations of egg yolk cholesterol and yolk granules in chick embryo development.