Evaluating the impact of housing modifications on milk infrared spectra as indicators of dairy cow welfare status.

The objective of this study was to explore whether milk mid-infrared (MIR) spectral patterns could reflect physiological responses to improved housing conditions aimed at enhancing dairy cow comfort and ease of movement. Three controlled animal trials were conducted to test the effects of housing modifications related to tie chain length (TCL), stall width (SW), and a combination of manger wall and stall length (MW/SL). A hybrid analytical approach combining principal component analysis (PCA) and mixed models was applied to identify spectral differences across treatments. In all three trials, housing modifications were associated with significant differences in spectral patterns, even in the absence of major shifts in traditional milk composition metrics. For example, cows with longer chains (TCL trial) showed spectral trends suggestive of changes in components such as milk non-protein nitrogen (NPN), trans fatty acids, fat, and protein, which aligned with patterns reported in association with changes in rumen pH. These results were consistent with concurrent behavioral observations indicating improved comfort. This study provides preliminary evidence that milk MIR spectra may be sensitive to subtle physiological changes linked to housing design, with differences observed between the most and least restrictive treatments, translating into improved or reduced animal welfare status. While not intended as a predictive tool for welfare status, the approach offers a non-invasive framework for investigating animal-environment interactions. Limitations related to sample size and scope are acknowledged, and further work is needed to validate these findings across larger and more diverse populations.