7.2. Assessing the pregnancy status of dairy cows by mid-infrared analysis of milk

In dairy cattle, unlike other species, performance recording schemes make it possible to provide advisory tools which integrate information across the whole population. Mid-infrared (MIR) analysis of milk provides a spectrum for each individual cow’s milk sample. The MIR spectrum represents the whole milk composition and can be used to assess the status of the animal (e.g. health, pregnancy, feeding). The main objective of the European project OptiMIR (INTERREG IVB North West Europe Programme) is to develop innovative advisory tools based on the MIR data collected by milk recording organizations. One of the objectives is to develop a tool to assess the pregnancy status of cows. The tool uses an innovative comparison of observed spectra with expected spectra predicted from a set of spectra with a known cow status, in this case open. Development was carried out using Walloon milk recording data. A training dataset (348,191 spectral data from 49,849 cows) was used to obtain residual spectra (i.e. difference between observed and expected spectra). Based on the fact that the pregnancy status of all cows was known, a predictive discriminant function was constructed using 7,524 residual spectra randomly selected from the initial dataset. The discriminant function was then applied to the rest of the dataset (24,278 residual spectra) for validation. When considering the period from 21 to 50 days after insemination, the error rate was about 7.5 with a specificity of 95.3 and a sensitivity of 87.2\%. These results showed a high potential for directly using the MIR spectrum of milk to detect a change in the pregnancy status of dairy cows. This methodology can also be applied to predict other types of physiological status changes (e.g. udder health related) and can be used on other types of biomarker data (i.e. collected from on-farm sensors). Similarly, integration of on-farm information on expected pregnancy status could improve the off-farm tool presented here.