RELATIONSHIPS OF POLYMORPHISMS FOR GROWTH-HORMONE AND GROWTH-HORMONE RECEPTOR GENES WITH MILK-PRODUCTION TRAITS FOR ITALIAN HOLSTEIN-FRIESIAN BULLS

Allelic variation in the structural or regulatory sequences of growth hormone and its receptor genes might directly or indirectly affect mil k traits. This possibility prompted us to investigate the eventual rel ationships of restriction fragment length polymorphisms at the locus o f bovine growth hormone (using TagI and MspI restriction enzymes) and its receptor (using TaqI restriction enzyme) production traits of bull s. Holstein-Friesian bulls were used in this experiment, and data were analyzed with a fixed linear model. The restriction fragment length p olymorphisms at the growth hormone locus did not affect the milk trait s studied. Six restriction enzyme TaqI bands of 7.1, 6.2, 5.7, 5.4, 4. 2, and 3.3 kb with nine patterns were observed after hybridization by a cDNA probe containing the coding sequences for the intracellular C-t erminal part of the receptor. The effect of this polymorphism on PTA f or milk protein percentage was highly significant and was favorable fo r the rare (6.6%) 5.7- and 5.4-kb pattern. Our results indicate that f urther study is needed to explain the DNA polymorphism and to obtain m ore definite conclusions about effects on milk traits.