Single fluff spray application of MHUSA (mother hen uropygial secretion analogue) positively influences Bursa of Fabricius development and the Heterophil to Lymphocyte ratio in ROSS 308 chicks

ABSTRACT Stress is an important cause of illness and mortality in chick production. Stressors such as manipulation, absence of maternal care, transport and housing can lead to welfare issues, immunodepression and decreased productivity. The mother hen uropygial secretion analogue (MHUSA), a synthetic analogue of a maternal semiochemical secretion, has been proven to protect chicks and broilers against stress, significantly reducing the heterophil to lymphocyte ratio. The aim of the present study was to test the effects of MHUSA on chicks’ stress when single-sprayed on their fluff at the age of 1 day. Two-hundred and eighty ROSS 308 chicks were included in the study. At day 1, each chick received a spray of 200 μl of a 2% MHUSA aqueous solution (140 chicks) or the same amount of the excipient (control group, 140 chicks), and then chicks were housed in two separate rooms. To assess the persistence of MHUSA after this single application, fluff was sampled from 10 chicks every day for 7 days and at day 13 and 19, weighed, placed in dichloromethane and analyzed by gas chromatography. Blood smears and the bursa of Fabricius were collected every 3 days from 10 chicks of each group for 36 days to assess the heterophil to lymphocyte ratio and the bursa weight to body weight ratio, respectively. Gas chromatography analysis showed that MHUSA was present on chick fluff until day 5. The statistical analysis revealed that the heterophil to lymphocyte ratio was lower in the MHUSA group at day 4, 7 and 9 (p