Plasma hormone concentrations in pasture-fed Friesian cows
treated with recombinantly-derived bovine somatotropin (bST)
S.N. McCutcheon, C.J. Hoogendoorn, G.A. Lynch, B.W. Wickham,
B.H. Breier, P.D. Gluckman
Department of Animal Science, Massey University, Palmerston
North, New Zealand
Proceedings of the New Zealand Society of Animal Production.
1991, 51: 235-238
Friesian cows (25 per group) were treated with excipient or
recombinantly-derived bovine somatotropin (bST, 25 mg/day) by two-
weekly injection of a controlled release formulation for 26 weeks
commencing 7 to 11 weeks after calving. Responses in fat yield were
significant during weeks 1 to 13 of treatment (spring/early summer) and
weeks 21 to 25 (autumn) but not during the intervening dry summer period
when pasture allowance was low. Ten randomly-selected cows per group
were blood sampled (tail vein, 2 hours off pasture) in weeks 5, 9, 13,
17, 21 and 25 of treatment. Treatment of cows with bST significantly
elevated plasma concentrations of immunoreactive bST (12.4 vs 18.5
ng/ml,Pooled se = 0.8 ng/ml, P<0.001) and insulin-like growth factor-1
(IGF-1) (178.5 vs 246.1 ng/ml, Pse = 7.5 ng/ml, P<0.001). Treatment x
sampling date interactions were non-significant for plasma levels of both
bST and IGF-1, reflecting parallel changes in the concentrations of
these hormones across the treatment period. It is concluded that the
inability of cows to respond to exogenous bST during periods of low
pasture availability does not reflect a diminished IGF-1 response to
bST at this time.
Keywords: NZSAPAB;
Bovine somatotropin, insulin-like growth factor-1; lactation
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Last Updated 25-01-1997
