Largescale analysis of chronic stress in dairy cows using hair cortisol and blood fructosamine (general introduction)

Stress in dairy herds can come from many sources. When stress becomes chronic due to long duration and inability of
animals to adapt, it can affect the emotional state, health, immunity, fertility and milk production of cows. It therefore
has a negative impact on the welfare, economy and social acceptability of dairy farms. Knowing the practices that
influence chronic stress would allow proposing strategies to improve animal welfare on farms. The study aims to
better understand the relationship between two chronic stress biomarkers and potential explanatory variables related
to production, management, health and housing. From a past research, two molecules were identified as biomarkers
of chronic stress: capillary cortisol and blood fructosamine. Based on 1,372 ELISA measurements of hair cortisol
and blood fructosamine, we studied their variability from 23 qualitative and quantitative features related to the herd
management practices collected in 77 farms from 5 different countries (Austria, Belgium, France, Germany, and
Luxembourg). The qualitative variables included information on cow diet type, management and housing system.
The quantitative features included information on cow characteristics, milk composition, housing conditions, udder
health, body condition score, and lameness. Principal components analysis and multivariate regressions highlighted
the differences in cortisol and fructosamine results between farms, and relate them to the different herd management
practices implemented on each farm. Preliminary results show that there may be multiple sources of stress, but that
cortisol and fructosamine levels appear to be strongly influenced by overcrowding. These first and subsequent results
could help to identify sources of chronic stress and provide useful guidance to dairy farmers to improve animal welfare.