M. Binelli et al., COMPARISON OF GROWTH HORMONE-RELEASING FACTOR AND SOMATOTROPIN - BODYGROWTH AND LACTATION OF PRIMIPAROUS COWS, Journal of dairy science, 78(10), 1995, pp. 2129-2139
Growth hormone-releasing factor is the main endogenous stimulator of s
omatotropin secretion. Our objective was to compare the effects of rec
ombinant growth hormone-releasing factor and recombinant bST on somato
tropin secretion, mammary function, and body composition of lactating,
primiparous dairy cows. Cows (118 d of lactation) served as uninfused
controls or were infused for 63 d with 12 mg/d of releasing factor or
with 29 mg/d of bST. These doses elevated somatotropin in serum to co
ncentrations of similar magnitude. The releasing factor and bST each s
imilarly increased milk yield, yield of milk components, weight of mos
t organs, mobilization of adipose tissue, accretion of lean tissue in
the carcass, and metabolic activity (RNA) of mammary tissue. Relative
to controls, neither releasing factor nor bST significantly affected c
ell numbers (DNA) in mammary glands or concentrations of plasmin in mi
lk. None of the variables measured provided evidence for galactopoieti
c effects of releasing factor independent of somatotropin.