P.J. Eppard

Variants of somatotropin in cattle: gene frequencies in major dairy breeds and associated milk production

The amino acid sequence of bovine somatotropin (bST) varies at position 127 where either valine or leucine is found. The frequencies of leucine127 and valine127 bST gene alleles in cows (n = 302) and sires (n = 70) from major dairy breeds (Holstein, Brown Swiss, Guernsey, Jersey, and Ayrshire) were determined using DNA extracted from whole blood or spermatozoa. A 428 base pair fragment of the bST gene was amplified using polymerase chain reaction (PCR) and variants of the bST gene were detected as polymorphisms by Alu I restriction endonuclease digestion of PCR products. Restriction enzyme DNA fragments for the leucine127 variant were 265, 96, 51, and 16 base pair and for the valine127 variant were 265, 147, and 16 base pair as a polymorphism of bST was present in the 147 base pair DNA fragment. Frequencies of leucine127 and valine127 alleles for cows (n = 302) were 1.0 and 0 for Brown Swiss, .93 and .07 for Holstein, .92 and .08 for Guernsey, .79 and .21 for Ayrshire, and .56 and .44 for Jersey, respectively. In Holstein sires used for artificial insemination (n = 70), the frequency of leucine127 and valine127 alleles was .96 and .04. Estimates of transmitting ability for milk production tended to be greater for Holstein cows that were homozygous for leucine127 bST and Jersey cows that were homozygous for valine127 bST whereas Holstein sires with different bST genotypes were similar. In summary, frequencies of alleles for the bST gene were not similar in different dairy breeds and estimates of milk production were correlated with bST gene variant in cows but not sires.

BIOLOGICAL ACTIVITY OF AMINO-TERMINAL AMINO ACID VARIANTS OF BOVINE SOMATOTROPIN

Publisher Summary This chapter discusses the biological activity of amino-terminal amino acid variants of bovine somatotropin (bST). Recombinant DNA techniques were used to produce individual analogues of the bST species found in pituitary preparations. The purified analogues were tested to determine the biological activity of the individual components of pituitary bST preparations. Oligonucleotide-directed, site-specific mutagenesis of the bST structural gene was used to prepare genes coding for the 6 analogues of pituitary bST species which includes ala(l) leu(127) bSTand ala(1) val(127) bST and met(1) leu(127) bST and met(1) val(127) bST and deletion (aa 1 -4) leu( 127) bSTand and deletion (aa 1-4) val(127) bST. The purified 191 amino acid proteins leu(127) bST, ala(1) val(127) bST, met(1) leu(127) bST, and met(1) val(127) bST, showed equivalent activity when tested in a bovine liver radioreceptor assay, in an anti-insulin assay utilizing 3T3L1 adipocytes, and in rat weight gain assays. It is found that when administered to dairy cows as a 25 mg daily intramuscular injection, all 4 somatotropins increased 3.5% fat-corrected milk production above control. N-terminal methionine and alanine bSTs increased FCM to the same extent.