PIT-1 GENE POLYMORPHISM, MILK-YIELD, AND CONFORMATION TRAITS FOR ITALIAN HOLSTEIN-FRIESIAN BULLS

The growth hormone factor-1/pituitary-specific transcription factor Pi t-1 is responsible for the expression of growth hormone in mammals. Mu tations in Pit-1 have been found in growth hormone disorders of mice a nd humans. We studied the eventual association between Pit-1 polymorph ism using the HinfI enzyme and the milk yield and conformation traits of 89 Italian Holstein-Friesian bulls. A strategy employing polymerase chain reaction was used to amplify a 451-bp fragment from semen DNA. Digestion of polymerase chain reaction products with HinfI revealed tw o alleles: allele A was not digested (451-bp fragment), and allele B w as cut at one restriction site, generating two fragments of 244 and 20 7 bp. Three patterns were observed; frequencies were 2.2, 31.5, and 66 .3% for AA, AB, and BB, respectively. Fixed and mixed linear models we re fitted on daughter yield deviations for milk yields and on deregres sed proofs for conformation traits. Predictions were weighted using th e inverse of the estimated variance of records. The models used contai ned mean and gene substitution effects for Pit-1 A allele as fixed eff ects and random sire effect for the mixed model. The A allele was foun d to be superior for milk and protein yields, inferior for fat percent age, and superior for body depth, angularity, and rear leg set, which is difficult to explain. A canonical transformation revealed that Pit- 1 had three actions, one linked to milk yield traits and angularity, a second linked to body depth and rear leg set, and a third linked to l ower fat yields and to higher angularity.