Genetic parameters and characterization of egg content spreading area in White Leghorn chickens

Uncharacteristically large spreading area on a flat surface of broken egg negatively affects egg quality assessment and reduces eggs' economic value. In this study, we investigated the heredity of the egg content spreading area as well as the relationships between the egg content spreading area and egg quality traits and properties. We measured the total egg content spreading area (TECA), outer thin albumen area (OTAA), inner thick albumen area (ITAA), yolk area (YA), and egg quality traits for 1414 newly laid eggs from 487 27-wk-old White Leghorn pure line pullets. The genetic parameters of egg content spreading areas were estimated. The phenotypic and genetic correlations between egg content spreading area and egg quality traits were analyzed. The differences in the properties of eggs with similar egg weight but markedly different TECA were also analyzed. The heritability estimates for TECA, OTAA, ITAA, and YA were low to moderate, with values of 0.214, 0.176, 0.340, and 0.280, respectively. Egg weight was related to TECA with a phenotypic correlation of 0.450 (P < 0.01) and a genetic correlation of 0.349. A high genetic correlation (-0.731) was found between TECA and Haugh unit. In eggs with larger TECA, the weight and total solid content of outer thin albumen (OTA) and moisture content of inner thick albumen (ITA) were significantly higher, whereas the weight and total solid content of ITA was markedly lower, but no differences (P > 0.05) were found in the pH of OTA and ITA, moisture content of OTA, as well as the eggshell strength, thickness, and non-destruction and fracture deformation between eggs with similar egg weight but markedly different TECA. These results suggest that the egg content spreading area can be regulated via the direct selection strategy or indirect selection of the ratio of OTA to ITA in the breeding program.

Effects of dietary L-carnitine on the performance and egg quality of laying hens from 65-73 weeks of age

The effects of L-carnitine supplementation (50-500 mg/kg diet) of a practical layer diet, based on maize, soyabean and wheat, on the performance of laying hens and some indices of egg quality were studied for 8 weeks, using 65-week-old hens kept in cages. Albumen quality (albumen height and Haugh (1937) unit score) was improved, while yolk index and yolk colour score were not affected by dietary L-carnitine. The percentage of egg-white increased and that of egg yolk decreased in response to dietary supplementation of L-carnitine. Dietary L-carnitine did not influence laying performance (egg production rate, mean egg weight, daily feed intake, daily egg mas and feed conversion) or external egg quality measured by egg weight, egg-shape index or by eggshell quality, either measured directly as shell breaking strength or indirectly as shell weight, shell thickness or shell weight per unit surface area. Based on the results of the present study, L-carnitine had a beneficial effect on albumen quality and could modify the components of the edible part of the egg, during the late laying period.

Source of carbon for the biosynthesis of eggshell carbonate in the hen. Comparison of six 14C labeled compounds as sources of carbon in eggshells, albumen, and yolk

Laying hens received single-dose intravenous injections of one of six U-14C labeled metabolites (bicarbonate, acetate, D-glucose, glycine, L-leucine, and palmitate) at times coinciding with maximum shell formation. Eggs were collected and 14C activities in shell, yolk, and albumen were measured. Typical patterns of 14C incorporation were observed with each of the three egg fractions; in shells highest 14C activities were obtained on the first postinjection day (D+1 day), albumen on the D+2 day, while yolks increased gradually their activities from zero levels on the D+1 day, reaching a plateau at around the D+4 day. In the second experiment, the 14C entry into albumen was slower than in the first one, with bicarbonate effecting higher albumen activities in D+3 than in D+2 eggs. Levels of 14C entry into shells of eggs laid on the D+1 day by hens injected with bicarbonate, glucose, or acetate were similar; significantly lower levels were obtained with (listed in descending order) glycine, leucine, and palmitate. Highest activities in albumen were induced by the two amino acids, with leucine causing higher activities than glycine; progressively lower entries were obtained with glucose, acetate, bicarbonate, and palmitate. In yolks, highest activities were obtained with glucose, followed by leucine, acetate, glycine, palmitate, and bicarbonate. Unexpectedly high activities obtained in the albumen of the D+1 eggs, particularly with 14C supplied from glucose, indicate that 14C was transported during the shell formation stage into the egg. The physiological implications are discussed and a suggestion is made that the possibility of carbonate for shell formation being delivered to the site of this formation from the inside of the egg should not be overlooked.