Growth hormone gene polymorphism associated with selection for milk fat production in lines of cattle.

Fifty-eight calves of both sexes from lines of Red Danish dairy breed selected for high (n = 36) and low (n = 22) milk fat production, and 32 heifers from lines of Norwegian Red dairy breed selected for high (n = 16) and low (n = 16) milk fat yield were typed for two previously reported restriction fragment length polymorphisms (RFLPs) in the growth hormone gene. The RFLPs are consistent with: (1) an insertion(I)/deletion(D) of approximately 0.9 kb in the 3'-region of the growth hormone gene and (2) a polymorphic MspI(+/-) site in the third intron. A traditional RFLP procedure was used for typing the I/D polymorphism and a polymerase chain reaction (PCR) procedure was developed for typing the MspI polymorphism. Only the I-MspI(+) and D-MspI(-) haplotypes were found. In the Red Danish lines the frequency of D-MspI(-) haplotype was 0.28 in high line and 0.05 in low line calves, this difference was significant (P < 0.01). The corresponding frequencies in the Norwegian Red lines were 0.09 in the high line and 0.0 in the low line. Attempts to screen for RFLPs in the growth hormone receptor gene and in the insulin-like growth factor-I gene were unsuccessful.