Production and health responses of laying hens and growing broilers to dietary omega-3 fatty acid supplementation
Omega-3 fatty acids, specifically alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) are known for possessing anti-inflammatory and bone modulating properties in murine and in vitro models. Health conscious consumers have created market demand for value-added omega-3 fatty acid enriched food, as demonstrated by the fact that specialty eggs make up 26.4% of the shell egg market. This has led producers to supplement poultry diets to create enriched eggs and meats and satisfy consumer demand. Thus far, omega-3 fatty acid research has primarily focused on creating value-added foods for the consumer with little attention paid to the effects of supplementation on the animals. The overarching goal of this dissertation research was to investigate the potential positive effects related to poultry health of dietary omega-3 fatty acid supplementation as a secondary benefit for producers. Two models were used to pursue the overarching goal: aged hens with mature immune systems at risk of osteoporosis and growing broilers with naïve immune systems prone to leg bone pathology. The experimental objectives of this dissertation were as follows: 1) Evaluate how dietary ALA sources affect the fatty acid transfer rate from laying hen diet to the egg yolk; 2) Determine if dietary supplementation of ALA or the combination of EPA and DHA improves performance and bone health of aged laying hens and whether protective anti-inflammatory effects would be exerted during acute inflammation; 3) Investigate if dietary supplementation of ALA or EPA and DHA impact bone health and performance in growing broilers, and 4) Examine the protective anti-inflammatory and bone modulating effects of ALA or EPA and DHA on broiler performance and health during a period of repeated inflammation. To evaluate dietary ALA sources and their fatty acid transfer rate to egg yolk (Objective 1, Experiment 1), diets supplemented with flaxseed oil or ground flaxseed were fed to Hy-Line W-36 laying hens near peak production for 8 wk. Egg yolk fatty acid profiles were measured to determine the transfer rates for the ALA sources. To determine if ALA or EPA and DHA affect bone health and inflammatory status of aged hens (Objective 2, Experiment 2), near end-of-second-cycle laying hens (122 to 134 wk of age) were fed diets supplemented with flaxseed oil or fish oil for 12 wk, followed by an acute lipopolysaccharide (LPS) inflammatory challenge. During the 12 wk dietary supplementation period, feed intake (FI), egg production, and egg weight were measured; and eggs and tibia were measured for strength prior to the inflammatory challenge. Liver inflammatory gene expression was measured 12 h post-LPS challenge. To investigate if ALA or EPA and DHA affect the bone health and performance of growing Ross 308 broilers (Objective 3, Experiment 3), diets supplemented with flaxseed oil or fish oil were fed for 28 consecutive d. FI, body weight (BW), breast yield, lameness, and bone mineral content (BMC) and density (BMD) were evaluated. Finally, to examine the protective anti-inflammatory effects of ALA or EPA and DHA on broiler performance and health (Objective 4, Experiment 4), the broilers from Experiment 3 were subjected to a 7 d repeated LPS inflammatory challenge, with the LPS dosage continually increasing by 20% every 48 h. Broiler BW and FI were measured from 35 to 42 d of age. Liver, muscle, and bone were measured for gene expression and composition. Results of the first experiment showed that the laying hens deposited ALA into egg yolk at a rate of 1.9 times more when fed flaxseed oil compared to ground flaxseed and total omega-3 fatty acids (ALA, EPA, and DHA) at a rate of 2.0 times more at the same dietary flaxseed oil concentrations, demonstrating the use of an extruded oil as a more efficient omega-3 fatty acid supplement than a ground seed (P ≤ 0.01). It was also observed that it might take up to six wk for transfer efficiency to stabilize and plateau in laying hens. The results from Experiment 1 were used for predicting omega-3 fatty acid transfer to egg yolk in Experiment 2 and as the basis for using oil as an ingredient source and selecting timeframes for diet acclimation for the experiments. The second experiment revealed that feeding aged hens EPA and DHA reduced average daily FI by 0.8 ± 0.19 g/hen and egg weight by 2.39 ± 0.556 g compared to control hens (P ≤ 0.01). Feeding hens ALA supplemented diets resulted in increased average daily FI by 1.2 ± 0.19 g/hen g compared to control hens (P ≤ 0.01). Feeding dietary ALA or EPA and DHA did not affect keel bone conformation score, tibia bone ash, tibia breaking strength, or eggshell breaking strength in aged hens (P ≥ 0.13). However, in response to the acute inflammatory challenge, feeding hens ALA or EPA and DHA resulted in intermediate gene expression levels of liver pro-inflammatory cytokines interleukin 1 beta (IL-1β), IL-6, and IL-18, and the adipogenic mediator peroxisome proliferator factor gamma as compared to the control hens (P ≤ 0.05), demonstrating anti-inflammatory protection. Further testing was conducted using a broiler model with growing bones and developing immune system to determine if administration of ALA or EPA and DHA at an earlier age would result in health and performance benefits. Results of the third experiment demonstrated that feeding broilers diets supplemented with ALA or EPA and DHA did not improve BMC (P = 0.21) or BMD (P > 0.05) compared to the control. However, ALA supplementation increased broiler BMD by 10% compared to EPA and DHA supplementation (P ≤ 0.05), while control was intermediate. Feeding EPA and DHA decreased 34 d broiler breast muscle yield by 1.301 ± 0.3553% compared to the control. Moreover, the broilers fed EPA and DHA decreased 34 d BW by 9% and increased feed conversion by 11% compared to the control and ALA supplement (P ≤ 0.05). Results of the fourth experiment demonstrated that the repeated LPS challenge in broilers reduced 42 d BW by 4% and FI by 6% compared to saline injections (P ≤ 0.01). Feeding EPA and DHA resulted in increased total lean tissue body composition in broilers by > 4% compared to the control and ALA supplemented diet (P ≤ 0.01). A protective effect was observed in broilers fed EPA and DHA, resulting in reduced liver gene expression of pro-inflammatory cytokines IL-1β, IL-6, IL-18, and IFNγ by 0.38, 0.21, 0.62, and 0.62-fold, respectively, compared to the control (P ≤ 0.05). Broilers fed EPA and DHA also experienced reduced liver gene expression of anti-inflammatory cytokine IL-10 by 0.41-fold compared to the control (P ≤ 0.01). Feeding broilers ALA or EPA and DHA supplemented diets increased total BMC by ≥ 0.2 ± 0.03 g and BMC accretion by ≥ 3.625 ± 0.9263% compared to the control (P ≤ 0.01). Collectively, omega-3 fatty acid supplementation did not improve or mitigate performance losses during periods of inflammation regardless of poultry model. The only instance where supplementation demonstrated a benefit to bone health was at therapeutic levels (4.1% ALA or EPA and DHA) during repeated inflammation in growing broilers. However, therapeutic levels of oil (14% oil used in Experiments 3 and 4) may not be practical to use in commercial broiler diets due to the limitations of feed manufacturing. Anti-inflammatory effects were achieved in the aged laying hen and naïve broiler models, but actively suppressing the immune system may not necessarily equate to a benefit to animal health. Anti-inflammatory effects in poultry housed in research or clean environments with low bacterial loads would allow a shift in metabolic activity from the immune system to productive activity. Commercial poultry live in microbial laden environments and immune suppression may allow opportunistic infections to occur, such as with Gram-positive bacteria or viruses; therefore anti-inflammatory effects would not be a benefit in these scenarios. Based on the experiments in this thesis, omega-3 fatty acid supplementation in poultry diets would not provide a practical secondary benefit for producers.
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