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In Pursuit of a Better Broiler: Tibia morphology, breaking strength, and ash content in conventional and slower-growing strains of broiler chickens

2021 CPRF
The rapid growth rate observed in fast-growing strains of broiler chickens has been linked to bone disorders that can cause lameness. Thus, the use of slower-growing (SG) strains has been suggested as an alternative for improved bone quality. To determine the impact of growth rate on bone traits, a total of 7,216 mixed-sex birds representing 14 strains were investigated, including 2 conventional (CONV) strains (strains B and C: ADG0-48 > 60 g/d), and 12 SG strains categorized in 3 groups based on their growth rate. The SG strains were classified as FAST (strains F, G, I, and M; ADG0-62 = 53 – 55 g/d), MOD (strains E, H, O, and S; ADG0-62=50 – 51 g/d), and SLOW (strains D, J, K, and N; ADG0-62 < 50 g/d). The birds were sexed at hatch and placed in 164 pens (44 birds/pen, 30 kg/m2). Each strain was represented in 4 pens over 2-3 production cycles, totaling 8-12 pens per strain in a randomized incomplete block design. From each pen, 4 birds (2 males and 2 females) were individually weighed and euthanized at 2 target weights (TWs) according to the time they reached 2.1 kg (TW1: 34 d for CONV and 48 d for SG strains) and 3.2 kg (TW2: 48 d for CONV and 62 d for SG strains). Tibia samples were dissected, length and diameter recorded. Left tibia was used for bone-breaking strength at both TWs and tibia ash at TW2. Data were analyzed using Proc Glimmix in SAS 9.4. For all of the models, category, strain, sex, TW, and the interactions were fixed effects, and block and production cycle random effects. For comparisons at the same age (48 d), category, strain, and sex were fixed effects, and the interactions were kept if significant. At TW1, CONV birds’ tibia were narrowest and shortest (P < 0.001), yet had similar tibia breaking strength (TBS) compared to the other categories (P > 0.69). At TW2, categories (P > 0.50) had no effect on tibia diameter, yet CONV birds had the shortest tibia (P < 0.001). The CONV birds had greater TBS:BW ratio than FAST and MOD birds at TWs 1 and 2 (P < 0.039). The CONV birds had the lightest tibia ash weight relative to BW (P < 0.001) and lighter absolute tibia ash weight than FAST and MOD birds (P < 0.009), yet similar ash content to the other categories (P > 0.22). At the same age, CONV birds had the greatest absolute TBS (P < 0.003), yet lower TBS:BW ratio than SLOW birds (P < 0.001). At a similar age (48 d), tibia from CONV birds were longer than MOD and SLOW birds, and thicker in diameter than the other categories, yet CONV birds had the lowest relative dimensions (P < 0.001). In conclusion, both genetic selection for growth and age affected bone traits. Future studies should investigate if the differences observed impact walking ability and welfare of broiler chickens.
Tags :
bone health,slow growing broilers
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PhD Student

University of Guelph

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