Isoelectric focusing reveals additional casein variants in German sheep breeds

Isoelectric focusing (IEF) was applied for screening milk protein variants in milk samples from altogether 1078 sheep of different breeds, in detail Black Faced Mutton sheep (SKF; n = 57), East Friesian Milk sheep (OMS; n = 254), Gray Horned Heath (GGH; n = 190), Merinoland sheep (MLS; n = 363), Merino Mutton sheep (MMS; n = 88), and Rhön sheep (RHO; n = 126). Besides the known genetic variants of αs1-casein (CSN1S1) (A, C, D), αs2-casein (CSN1S2) (A, B), and β-lactoglobulin (LGB) (A, B, C) additional variants could be demonstrated in CSN1S1 (H, I) and CSN1S2 (C, D) and their genetic control confirmed by segregation analyses. CSN1S1*H corresponds to a previously mentioned phenotype “X” occurring in OMS, whereas CSN1S1*I was identified for the first time in GGH. CSN1S2*C appeared in OMS, GGH, MLS, and RHO in low frequencies and CSN1S2*D in MLS. Within LGB all three alleles occurred in Merino breeds while α-lactalbumin (LAA) and κ-CN (CSN3) were monomorph at protein level. The haplotype CSN1S1*C–CSN1S2*A was predominant in five out of six breeds with frequencies between 0.325 and 0.919.