Milk testing is able to provide a valuable, non-invasive resource for monitoring the biometrics of an animal, in particular for the agricultural monitoring of cows. Information of interest includes the presence and concentrations of such compounds as lactose, antibiotics and hormones. The former two can give an indication of animal health as well as the suitability for human consumption, while the latter provides information on animal fertility. Within the milk matrix exists a range of compounds including proteins, fats, and sugars that can serve to complicate the detection of target species, or may indeed be the target compounds of the sensors. Biosensor platforms can combine the selectivity and sensitivity of biological systems together with the potential for straightforward sensor read-out, rapidity, portability and automation for online analysis. However, there are hurdles to overcome to provide stable, sensitive, reproducible sensors able to perform measurements in the real-sample milk matrix. This chapter describes milk components, specific compounds that may be detected in milk, biosensing methodologies for milk sample analysis, and a review of selected literature, focusing specifically on the milk matrix and real sample testing.