PHYSIOLOGICAL DIFFERENCES IN LATE EMBRYOS FROM TURKEY BREEDERS AT DIFFERENT AGES

Physiological mechanisms were measured in embryos from turkey hens of different ages to determine associations with declines in hatchability as breeder hens age. As the hens aged from 32 to 54 wk of age, embryo nic viability declined (P < 0.05). The greatest proportional increase (P < 0.01) in embryonic mortality of aging hens occurred at the platea u stage in oxygen consumption or immediately thereafter at pipping Egg shell conductance constants increased (P < 0.01) as hens aged but did not change after mid-lay, suggesting an alteration in respiration for the embryos in eggs produced by older hens compared to eggs produced b y the same hens at younger ages. The alteration may cause embryos in e ggs from older hens to reach the plateau stage in oxygen consumption ( approximately 25 to 26 d of incubation) earlier in development than em bryos from young hens. Hepatic and cardiac glycogen concentrations wer e greatest (P < 0.001) in embryos from hens at the youngest age and th en declined (P < 0.05) as the hens aged. Embryonic blood plasma glucos e concentrations declined (P < 0.05) similarly. Plasma thyroxine (T-4) and triiodothyronine (T-3) concentrations were measured in embryos fr om the hens at different ages as well. Increased (P < 0.05) T-4 was ev idenced in embryos from the youngest hens, whereas increased (P < 0.05 ) T-3 activity was evident in embryos from hens of older ages. It was concluded that the decline in hatchability seen as turkey breeder hens age may have a basis in the differences seen in the physiology of hat ching in embryos. Specifically, thyroid influences on growth and carbo hydrate metabolism may be involved in decreased embryonic viability.