RbST is a proteohormone that can be used to increase milk production, but its administration is illegal in the EU [16 ] and of consumer’s concern in the USA. To detect rbST abuse, it has been shown that rbST-dependent protein biomarkers in serum and milk of dairy cows can be monitored, but levels are typically low (10 ng mL -1 range) [17 –19 ].
Source: wiktionary