Identifying an optimum ω3:ω6 dietary content to improve bone health for laying hens with minimal detrimental impacts on production endpoints

Introduction Keel fractures in laying hens is a serious welfare issue with up to 70% of birds within a flock having fractures. Their occurrence is likely owed to a combination of factors, including poor calcium retention and housing system. Our group has been researching using ω3-enhanced diets as a means to improve bone strength and reduce fractures following preliminary experiments indicating short chain ω3-based diets reduced fractures by 30-50% in commercial settings. Despite this finding, more recent work using a mixture of long and short chain ω3 content failed to deliver similar benefits to bone health and fracture level while increasing production losses. The current study was undertaken to identify whether reduced long chain content could yield benefits to bone health while minimizing negative impacts on production. Materials and Methods Thirty two Lohman Brown poultry layers were delivered to the University of Bristol, Langford Campus at approximately 23 weeks of age hereafter referred to as wk 0. Birds were randomly placed into one of eight pens across two rooms (4 birds/pen, 4 pens/room) and each pen provided ad-libitum access to one of four diets ranging in an ω3:ω6 of 0.12 to 1.35. Birds remained there until wk 12 whereupon they were killed by cervical dislocation, dissected with the keel, humeri, tibia, and caecal contents removed, which were then frozen at -80˚C until analysis. At weekly intervals, records were made of hen daily average, feed consumption, shell quality, and three normal eggs collected for assessment of shell width and biomechanic testing of two shell sections. At wk 7, a single egg from each pen (2 eggs/treatment) was collected for fatty acid analysis. Dissected tibia and humeri were used for quantification of bone mineral density and content using dual energy X-ray absorptiometry followed by biomechanic testing. To assess presence of keel fractures, birds were palpated upon arrival and again at wk 8 to assess the presence of keel fractures (Wilkins, et al. 2004) . At dissection, removed keels were visually assessed for fractures and then frozen until biomechanic testing. Lastly, to identify whether diet had an impact on the natural presence of campylobacterinfection rate in tissues, the presence and numbers of Campylobacter in the caecum and liver was established by direct plating of serial dilutions on mCCDA from samples collected during post-mortem. Data was statistically analyzed with MlwiN. The various responses were modelled as continuous variables with the exception of the presence of fractures which was modelled as a binary response. ω3:ω6 ration, week, and their interactions were included as continuous prediction variables with polynomial terms where applicable. Where repeated measures were taken (e.g., weekly production data), week was included in the model structure accordingly. Table 1 Biomechanic impact of diet on the tibia ω3:ω6 Measure 0.12 0.36 0.83 1.35 Pooled SD Diet1 x^n2 Ultimate Force (N) 210.48 222.20 206.18 223.55 35.82 ns - Ultimate Strain (mm) 1.84 2.07 2.06 2.04 0.28 ns - Ultimate Joule (E-1) 2.51 2.90 2.81 2.79 0.69 ns - Yield Stress (N) 95.45 93.99 96.01 103.52 19.98 ns - Yield Strain (mm) 0.31 0.30 0.34 0.31 0.06 ns - Young's Modulus 32.02 29.86 26.50 33.03 7.12 0.04 2 Elastic:Plastic 0.08 0.05 0.06 0.06 0.03 ns - 1P-value of the treatment term with the greatest polynomial; ns = non-significant. 2Value of the highest polynomial associated with the treatment effect. Results The number of poor quality eggs was found to exhibit a positive dose-dependent correlation with ω3:ω6 ratio (p = 0.03). The side section of the shell exhibited a linear negative correlation to ω3:ω6 for work required to reach structural failure, i.e. greater ω3:ω6 resulted in weaker shells (p = 0.02). Several parameters assessing tibia bone biomechanics manifested a treatment effect, although only ultimate work exhibited the anticipated increase where ω3:ω6 ratio positively correlated to the amount of work required (p = 0.04; Table 1). No treatment effect was found for the presence of keel fractures (p>0.5), though portions of the keel where found to exhibit a treatment effect in biomechanic strengthultimate stress albeit in a non-linear fashion with values greatest in birds receiving the 0.36 and 1.35 rations. PUFA analysis of egg yolks found dose dependent increases in ALA and EPA though total long chain content appeared to level off beyond the 0.83 ration. Campylobacter concentrations in the caecum exhibited a treatment effect (p = 0.04) of a parabolic nature with the greatest value in birds receiving the 0.36 ω3:ω6 ration. Conclusions. Our data indicate that some of the long chain ω3 diets’ negative impacts (i.e., poor egg quality) can be alleviated relieved while sufficient ω3 egg yolk quantity is maintained by providing a mixture of short and long chain ω3 content. Benefits of mixed ration to bone and overall health are less clear and will require further research. Acknowledgements The authors wish thank Rossyew, Optivite, and Noble Foods and BBSRC for funding. References Wilkins LJ, et al. Vet Rec 2004;155:547-9.

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