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Impact of growth trajectory on sexual maturation in layer chickens

2021 CPRF
While domestic chickens are seasonal breeders, recent studies in our lab showed that apart from photostimulation, metabolic triggers may independently activate sexual maturation and egg production when a threshold is met. However, the origin, mode of action, and specific target(s) of this metabolic control, and whether it is strain dependent, remain unknown. Rather than body weight (BW), we hypothesize that body composition (BC) and associated specific metabolic signals are involved. Thus, this study was conducted to determine the BW and BC thresholds triggering spontaneous sexual maturation in 2 strains of layers under differing growth trajectories. Day old Lohman LSL lite (W) and Lohman brown (Br) layer chicks (n=210 each) were raised in brooding cages (n=15; 14 chicks/cage) under ad libitum (AL) feeding, with lighting schedule as per breeder’s recommendation. At 8 weeks of age (woa), pullets were randomly allocated into individual cages across two rooms (n=210 cages/room) and assigned to one of 3 experimental growth profiles, including AL, breeder’s target (T), restricted 20% below target (R), (n=70 birds /profile/ strain). All hens were maintained on 10 h of light (10 lux) throughout the rest of the study, with no photostimulation. Feed allocation for T and R birds were determined individually on a weekly basis based on actual BWs, with all hens fed the same commercial diet. Blood and tissue samples were collected throughout the study to measure estradiol (E2) levels and organ weights, respectively, and carcasses were subjected to DEXA (Dual-energy X-ray absorptiometry) analyses. All analyses were completed in SAS using the MIXED procedure. Our results show that R treatment slowed (P < 0.001) body growth, delayed age at first egg (FE) and egg production (P < 0.001), and resulted in lower BW at FE (P < 0.001), lower ovary weight and number of follicles (P < 0.001), and attenuated plasma E2 levels in both strains. In Br hens, a further delay in the E2 peak was observed. Interestingly, AL feeding resulted in higher growth rate and earlier age at FE (P < 0.001) for Br hens only. However, birds fed AL had a higher BW at FE (P < 0.001), higher follicle number and ovary weight (P < 0.001) in both strains. For DEXA, AL feeding (P < 0.001) increased tissue weight, lean weight, and fat deposition while R significantly reduced them (P < 0.0001). Of interest, fat deposition remained below 10% in Br hens until 22 woa, time at which a delayed peak in plasma E2 was observed. In conclusion, feed allocation impacted growth and BC in a strain dependent manner, resulting in differing sexual maturation and egg production. Whether these effects are mediated through hypothalamic input is under investigation.
Tags :
growth trajectory,layers,sexual maturation
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PhD Candidate

University of Guelph

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