SEQUENCE VARIATIONS IN THE BOVINE GROWTH-HORMONE GENE CHARACTERIZED BY SINGLE-STRAND CONFORMATION POLYMORPHISM (SSCP) ANALYSIS AND THEIR ASSOCIATION WITH MILK-PRODUCTION TRAITS IN HOLSTEINS

Sequence variations in the bovine growth hormone (GH) gene were invest igated by single strand conformation polymorphism (SSCP) analysis of s even amplified fragments covering almost the entire gene (2.7 kb). SSC Ps were detected in four of these fragments and a total of six polymor phisms were found in a sample of 128 Holstein bulls. Two polymorphisms , a T-->C transition in the third intron (designated GH4.1) and an A-- >C transversion in the fifth exon (designated GH6.2), were shown to be associated with milk production traits. GH4.1(c)/GH4.1(c) bulls had h igher milk yield than GH4.1(c)/GH4.1(t) (P less than or equal to 0.005 ) and GH4.1(t)/GH4.1(t) (P less than or equal to 0.0022) bulls. GH4.1( c)/GH4.1(c) bulls had higher kg fat (P less than or equal to 0.0076) a nd protein (P less than or equal to 0.0018) than GH4.1(c)/GH4.1(t) bul ls. Similar effects on milk production traits with the GH6.2 polymorph ism were observed with the GH6.2(a) allele being the favorable allele. The average effects of the gene substitution for GH4.1 and GH6.2 are similar, with +/-300 kg for milk yield, +/-8 kg for fat content and +/ -7 kg for protein content per lactation. The positive association of G H4.1(c) and GH6.2(a) with milk production traits may be useful for imp roving milk performance in daily cattle.