CHANGES IN FUNCTIONAL QUALITIES OF TURKEY EGGSHELLS IN STRAINS SELECTED FOR INCREASED EGG-PRODUCTION OR GROWTH

Much past research has been devoted to physical eggshell qualities, i. e., weight, deformation, or egg density, but little research has inves tigated the functional eggshell qualities when expressed in terms of e ggshell conductance to gases. Conductance is a measure of the ease wit h which gases diffuse across the pores of the shell and is (by Fick's law) determined by the number and geometry of the individual pores. Th e objective of the present study was to determine changes that have oc curred in functional eggshell characteristics (eggshell conductance) f ollowing selection for egg production or growth over nearly 30 generat ions. Major changes have occurred in the physical dimensions of eggs f rom selected lines of turkeys compared with their respective randombre d controls. Egg weights increased 11% due to selection for growth and decreased 14% due to selection for egg production. Other measurements such as length and width increased allometrically with egg weights. Se lection for egg production has decreased the physical dimensions (egg weight, volume, or surface area) of eggs, and selection for growth has increased the same measurements, but adjustments have not been made b y selected hens to increase or decrease the functional characteristic (conductance) allometrically (conductance constants). An interaction w as observed in eggshell conductance constants as the hens aged, sugges ting that genetic selection may affect functional characteristics. Thi s suggests that the energetics of embryonic development may be differe nt in eggs from turkey hens of various ages. Energetics may result in poor hatchability and poult quality. It can be concluded that as the h ens aged the conductance and conductance constants did not change allo metrically with increasing egg weight. This may suggest a reason for i ncreased embryonic mortality seen in the selected lines compared with their randombred control lines.