Going beyond current limits in defining and using milk infrared spectra based phenotypes

Mid-infrared (MIR) spectral data has been recognized as a major source for novel milk-based phenotypes for breeding and management. Current limits exist however in defining and using these phenotypes that are related to: (1) type of infrared technology and the associated sampling methods; (2) scope of reference traits; (3) used prediction models; (4) portability of prediction equations; and (5) use of results for breeding and management. The first limit is currently falling as on-farm in-line near-infrared (NIR) tools become available. This will also add real-time capacity to many novel applications pioneered in MIR. But due to sampling frequency, and ioff-line nature, MIR is lacking this capacity. Recently the scope of reference traits was considerably enlarged extending beyond milk components, the prediction of methane emissions, being an example. Also milk MIR spectral data is in general an excellent tool to check for the status of the cows (e.g. body energy). Two other recent examples reported here are the ongoing research on identification of cow’s heat stress status and the detection of early pregnancy in milk composition. Work on heat stress is starting to detect milk spectra based signatures of reduced intake and increased body reserve mobilization. Results based on pregnancy validated test-day records showed that in the period up to 90 days pregnant the relative reaction of certain MIR wavelengths were at least 2× larger than that of milk yield. The recently finished OptiMIR project has been instrumental in pushing back boundaries allowing improved portability of equations and novel applications. A final issue is the correct use of indirect (M)IR predictors, distinguishing (i.e. genetic correlations <1) MIR based indirect index traits from breeding goal (e.g. direct) traits. If the required (genetic) parameters become available, direct, and therefore optimal, use of MIR spectral data to complement direct traits will become possible.