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Impact of rearing environments on growth trajectories and sexual maturation in layer chickens

2022 CPRF,Layers
Our recent studies showed metabolic triggers can independently initiate sexual maturation when a threshold is met. Moreover, previous research showed that growth and body composition of layer pullets are influenced by rearing environments. Thus, this study aimed to determine whether different housing systems (HS) affect the metabolic threshold required to activate the reproductive axis in layers. Day-old Lohman LSL lite (W, n=224) and Lohman brown (Br, n=224) chicks were randomly assigned to either Conventional cages (CC, n=18), Aviary 1 (AV1, n=52, confined for the first 6 weeks), Aviary 2 (AV2, n=64, access to vertical space for the first 6 weeks) or Aviary 3 (AV3, n=90, open concept for the first 6 weeks) on a 2 x 4 factorial arrangement of treatments. At 6 weeks of age (woa) all systems (except CC) were opened to provide access to a litter area. All hens received ad-lib feed and lighting was scheduled as per the breeder’s recommendation. Body weight (BW) and blood samples (n=10 per group) were collected throughout the study and estradiol (E2) profiles were determined. At 16 and 23woa a subset of birds were euthanized (n=6) and carcass composition was determined by Dual-energy X-ray absorptiometry (DEXA). Statistical analyses were performed using the MIXED procedure in SAS. Results show that Br pullets were heavier (P < 0.001) than W and pullets in CC had higher BW compared to AV systems for both strains. The impact of HS was more pronounced for Br than W with pullets in AV1 and AV3 displaying the lowest BW (P < 0.001). The HS impacted sexual maturation in a strain-dependent manner with the E2 peak delayed by 2 weeks for W in AV3 and 3 weeks for Br in AV1 (P < 0.001). Egg-laying was also delayed for W in AV1 and AV3 (P < 0.001). Regardless of HS, Br started laying 1 week before W. Results of DEXA show that HS had a significant impact on carcass fat (P < 0.001) with pullets in CC reaching 20% fat ratio at 16woa for both strains while all 3 AV systems resulted in levels below 16%. At 23woa, the fat ratio in CC remained unchanged while levels in AV systems caught up, except for W in AV1. Bone mineral density was significantly reduced (P < 0.001) in CC pullets at 16woa, however, at 23woa, no difference was observed between treatments. At 16woa, W pullets displayed lower (P < 0.001) bone mineral density than Br. In summary, the results show that rearing pullets in CC results in increased body weight and carcass fat percentage while lowering bone mineral density at 16woa. The type of aviary system also had an impact on body weight and body composition, however, a significant concomitant impact on egg production was only observed in W birds.
Tags :
growth trajectory,rearing,sexual maturation
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PhD Candidate

University of Guelph

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