Serum lactate as a physiological indicator of broiler welfare

ONCE Director of Biologic Research and Development, Aaron Stephan, has presented our insights to use serum lactate as a physiolocical indicator of broiler welfare, at the annual meeting of the Poultry Science Association in Texas, July 13th 2022. Find below the abstract of the lecture.

 

Serum lactate as a physiological indicator of broiler welfare

Aaron Stephan*1, Curtis Leyk1, Jack Tieberg1
1Once Innovations, Chanhassen, Minnesota, United States

Abstract Body: Outcome-based measures of broiler welfare often require subjective scoring by trained personnel and rely on crude outcomes such as feather quality or scoring wound or gait impairments. Additional methods to quantify broiler welfare are accessible to the research community such as fear or stress-induced behavior tests and blood indicators of stress, such as Heterophil:Lymphocyte (H:L) ratios and corticosterone levels. However, these measures require a significant effort and associated cost and are therefore not feasible to be used as an audit tool in commercial applications. Stress activates the adrenergic pathway, which results in secondary elevations in lactate. Given the documented effects on the long-term metabolism of humans, other mammals, and reptiles resulting in chronic stress hyperlactatemia, we hypothesized that broilers housed in different environments may have measurable differences in blood lactate (lactic acid). To test this hypothesis, we first conducted an experiment where broilers were raised under commercial conditions using two light recipes: a standard white-light recipe and a second light recipe shown to reduce stress biomarkers and fear. H:L ratios were measured as well as five behavioral assays of fear and stress. Serum lactate was quantified via colorimetric microplate assay (Sigma Milipore Lactate Assay Kit II) and subsequently by a portable lactate meter using test strips (Nova Biomedical Lactate Plus). Serum lactate was detectible in a range from 0.3-25 mmol/L. Individual serum samples showed a significant correlation (linear regression analysis, p<0.001, R version 4.0.3) between the microplate assay and portable lactate meter values. Broiler chickens grown under the low-stress light recipe resulted in statistically significant reductions (average 8.003 vs 9.505 mmol/L) (p=0.00044, Student’s t-test, R version 4.0.3) in serum lactate compared to broilers grown under standard light recipe conditions. The Hypothalamic-Pituitary-Adrenal (HPA) axis was induced via repeated injection of dexamethasone, the resulting serum lactate levels were measured and analyzed via two-way ANOVA with Tukey’s post-test considering dexamethasone treatment and light treatment as factors (R version 4.0.3). The interaction between dexamethasone and light treatment was significant (p<0.001), suggesting that the HPA stress response may partially counteract stress-induced lactate. The advantages of using serum lactate as an indicator of welfare thus include speed (<1 minute per sample), low cost (<$2 per sample), and a highly quantitative nature. Further exploration of lactate as an indicator of broiler welfare is warranted.