Calcium Homeostasis in Pullets of Two Lines Selected for Differences in Eggshell Strength

Abstract

Lines were selected from the Cornell K Single Comb White Leghorn strain for two generations for high (HES) or low (LES) eggshell strength. Laying hens of both generations showed significant differences between lines in shell breaking strength. Hens of the second selected HES generation produced eggs with significantly better shell quality than did LES hens, as measured by shell breaking strength, shell thickness, or absolute or relative shell weight. However, the two lines had similar intrauterine egg residence times and times between successive ovipositions. The LES pullets showed significantly elevated ionized calcium and total calcium concentrations in blood in response to increased dietary calcium at 18 weeks of age. These results demonstrate fundamental differences in regulation of calcium homeostasis between the HES and LES lines which may relate to selected differences in their abilities to produce strong eggshells.

Percent Shell and Plasma Mineral Concentrations in Three Strains of Domestic Fowl Selected for Thick or Thin Egg Shell Production

“…Hens__producing TK or TN egg shells have similar intervals between successive ovipositions and similar in utero residence times (Stout and Buss, 1980), as do lines established elsewhere forjiigh or low egg shell jtrength (Combs et al, 1979). Because TK hens deposit more shell calcium than TN hens during the same length of time, and the sizes of TK and ^TN eggsjlo not differ_sjgnjficantly, the rate-of shell gland, calcium secretion_jiecessarily must be higher for 'Paper No.…”

“…Recent independent observations provide added support for these findings, because hens producing high specific gravity eggs have significantly higher plasma calcium levels than hens producing eggs of low specific gravity (Grander et al, 1983;Hamilton, 1981). Independent evidence also supports the finding that significant differences in shell quality can occur within one generation of selective breeding (Combs et al, 1979).…”

Fluorosis in the Laying Hen

“…The two strains had been developed as closed breeding populations with significantly different (by 15 to 20%) average eggshell breaking strength but with comparable egg sizes and levels of egg production (Combs et al, 1979). The two strains had been developed as closed breeding populations with significantly different (by 15 to 20%) average eggshell breaking strength but with comparable egg sizes and levels of egg production (Combs et al, 1979).…”

“…These strains have been selected in this laboratory (Combs et al, 1979) for differences in eggshell breaking strength as measured by quasi-static loading. For this purpose, two different strains of Single Comb White Leghorns were used.…”