Based on reference method measurements and Fourier transform infrared (FTIR) spectra, prediction equations for casein in raw milk were calculated. Subsequently casein content was predicted from multiple milk samples of 1.3 million cows from March 1, 2012, until February 23, 2013. After editing 8.5 million test-day records were available for analysis. The average casein content observed in milk was 2.77% (m/m), 77 percent of the total milk protein, with a standard deviation of 0.37% (m/m). Genetic parameter estimation was carried out on 61 000 Holstein cows, with 480 000 test days. The found heritability was 0.30, 0.34 and 0.39 for first, second and third lactation, respectively. The genetic correlation among the lactations ranged from 0.52 to 0.60. Genetic correlation with overall protein was 0.982. The genetic standard deviation for casein:protein ratio was 1.36 percent, with an heritability of 29 percent. The genetic correlation between casein:protein ratio and casein and protein yield was 0.23 and 0.35 respectively, while the phenotypic correlation was 0.01 lower, showing the ratio trait is independent from the yield traits. A genetic evaluation for protein yield and content, casein yield and content and casein:protein ratio was carried out on the whole population. This showed that selection for casein:protein ratio increases casein content but decrease casein and protein yield. In conclusion, casein yield showed to be a promising parameter in a cheese merit index. Efficient assessment of casein using the novel FTIR prediction equation allowed for access to sufficient data being available. This research was supported by the EU and the province of Gelderland, the Netherlands.