Lipid profile in eggs of Araucana hens compared with Lohmann Selected Leghorn and ISA Brown hens given diets with different fat sources

1. In a cross-over trial, the egg cholesterol and fatty acid composition of Araucana hens was compared with those of two commercial breeds (Lohmann Selected Leghorn and ISA Brown) under two feeding regimes, either high (Hn-3) or low (Ln-3) in long-chain n-3 fatty acids. 2. The Hn-3 diet was formed by isocaloric substitution of animal fat in the control diet (Ln-3) by a dry product containing stabilised fish oil with standardised concentrations of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). 3. Both breed and diet had influences on egg composition, without interactions. 4. The Araucana breed showed lower feed intake and lower egg weights than the other two breeds. The yolk weight was similar, leading to a much higher yolk:albumen ratio in the Araucana eggs. 5. In comparison to commercial breeds, Araucanas produced eggs with higher cholesterol content per g of yolk, which was even more pronounced when expressed per g of egg, due to the high yolk content of the eggs. The cholesterol content of an egg remained unchanged by the diet, irrespective of the dietary fat source. 6. Changing to the Hn-3 diet led to greater concentrations of polyunsaturated fatty acids (PUFA) and lower concentrations of monounsaturated fatty acids (MUFA) contents in the yolk, without a change in the ratio of saturated (SFA) to unsaturated fatty acids (UFA). 7. Within the PUFA, the n-3 fatty acids increased at the expense of the n-6 fatty acids, indicating a competition between n-3 and n-6 fatty acids for incorporation in the yolk.

Variation in egg yolk cholesterol concentration between and within breeds of the domestic fowl

1. The pattern of variation for egg yolk cholesterol concentration between 5 commercial egg layer lines and a cross of Gallus domesticus is described. 2. Yolk cholesterol concentration in the cross was lower than in the lines, and 6.7% lower than the midparent value. 3. It is proposed that the reduced yolk cholesterol concentration of the cross may be a consequence of heterosis, although sex-linkage and/or maternal effects cannot be discounted. 4. The difference between the cross and parental lines is consistent with a physiological relationship between yolk cholesterol concentration and rate of egg production, but not between yolk cholesterol concentration and yolk weight.

Yolk cholesterol in eggs from various avian species

Studies were conducted to establish the differences in yolk cholesterol concentrations in eggs from various avian species. Cholesterol was determined by a modification of the colorimetric procedure of Pearson et al. (1953). Species listed in increasing concentrations of cholesterol per gram of yolk, were guinea fowl, chicken, pheasant, quail, turkey, duck, goose, and dove with an overall range of 12.77 to 21.99 mg of cholesterol per gram of yolk. Significant differences in cholesterol concentrations also were found between domestic and wild genetic groups for turkeys and ducks. In a second study, eggs from 7 inbred lines of chickens showed significant differences in yolk cholesterol. The same general result was found in an analysis of eggs from 17 commercial test strains of chickens at two different ages. Yolk cholesterol tended to decrease as age of hen increased. These results confirm the possibility of genetically selecting for decreased yolk cholesterol if economic or other conditions warrant. The increased efforts required to decrease yolk cholesterol by this approach would undoubtedly be expensive.

Protein and cholesterol content of Araucana chicken eggs

Comparative data collected over two years are presented which refute the popular press claims that blue-shelled eggs of Araucana chickens have higher protein levels and lower cholesterol levels than market eggs. These comparisons were made between the eggs from the strains of Araucanas and those of White Leghorns and Sex-links. None of the differences found between test groups in % protein/g. albumen and % protein/g. yolk were shown to be consistently related to any one test group type. However, all Araucana test groups were significantly (P less than .01) lower in their total egg protein content than either control group by from 2.8--6.5%. This lower total protein content was the result of a consistent increase in the yolk/albumen ratio of the Araucana eggs over the market eggs. The Araucana eggs were consistently higher in their cholesterol levels on a mg./g. yolk basis than either of the market eggs. These increased concentrattions ranged from 2.0--6.9%.