Comparison of Embryo Physiological Parameters During Incubation, Chick Quality, and Growth Performance of Three Lines of Broiler Breeders Differing in Genetic Composition and Growth Rate

ABSTRACT In broiler breeder management, stringent feed restriction is practiced to reduce body size in order to improve egg production and meet broiler production demand, but this practice has raised welfare issues. The potential for the dwarfing (dw) gene to reduce feed intake and body size of breeders under ad libitum feeding or less stringent restriction while maintaining improved egg production has been reported. In this study, we compared embryo physiology, quality of chicks, and performance of broilers from eggs of dwarf breeders with those from a standard broiler breeder. Hatching eggs from 3 commer-cial lines of broiler breeders were compared for incuba-tion parameters, 1-d-old chick weight, chick quality, and broiler growth to 41 d of age. The lines included a stan-dard heavy (S) line, an experimental (E) line, and a label-type (L) line. The E and L line breeders carry the sex-linked dw gene and are being used to assess the potential for dw to reduce feed intake or lower feed restriction and improve reproductive performance in heavy female broiler parent stock. Two separate experiments were con-ducted. All female parent stocks were mated to Cornish males, and fertile eggs were collected. In the first experi-ment, eggs were incubated for 21 d under standard condi-tions to determine, during final stages of incubation, corti-costerone and thyroid hormone levels (triiodothyronine, T3; thyroxine, T4) in embryos and hatchlings, CO2 partial pressure (pCO2), and O2 partial pressure (pO2) in air cells, heat production by eggs and 1-d-old weights. In the sec-ond experiment, eggs were incubated for 21 d to compar