The importance of milk proteins and the positive effect of administration
of growth hormone (GH) on milk production, and the presence in some dairy
cattle
lines of greater GH concentrations prompted us to examine the presence
of
restriction fragment length polymorphism at the GH gene using the restriction
enzyme TaqI and to investigate associations between this polymorphism
in
Simmental cows and bulls, as well as milk protein variants in Simmental
cows, and
milk production traits. Blood and milk were sampled from 279 Italian Simmental
cows and semen was collected from 148 bulls of the same breed. Two fragment
bands,
denoted A and B, of 6200 and 5200 bp respectively, were examined and three
patterns, AA, AB and BB, were found in both animal samples. All variants
previously reported in other studies, for κ, β, and
αs1-caseins, and β-lactoglobulin,
were found in the cows' samples. For the cows' samples, a BLUP
(Best Linear
Unbiased Predictor) analysis of results was performed using a REML (Restricted
Maximum Likelihood) program and known heritabilities, whereas for bulls
we have
performed a General Linear Model analysis. The effect of GH gene polymorphism,
using TaqI restriction enzyme, on milk production traits was
not significant, but
bulls of BB pattern had a higher breeding value for milk yield than AA
bulls
(P<0·05). For the κ-casein genotypic effects,
cows of AB genotype gave milk with
1·53±0·70 g/kg less fat than cows of
AA genotype. In addition, breeding values for
milk protein content were significantly higher in BB bulls, with
0·87±0·32 and
0·71±0·34 g/kg more milk protein than AA and
AB bulls respectively. Thus, our
results revealed a GH gene polymorphism and indicated significant effects
of milk
protein polymorphisms on milk production traits in the Italian Simmental
breed.
Growth Hormone Gene Polymorphism and its Relation to Quail Growth and Carcass
