New Zealand Journal of Agricultural Research abstracts
Long-term bromocriptine treatment during late pregnancy has differential
effects on milk yields of single- and twin-bearing ewes
S. W. PETERSON
D. D. S. MACKENZIE
S. N. MCCUTCHEON
Department of Animal Science
Massey University
Palmerston North, New Zealand
K. R. LAPWOOD
Department of Physiology and Anatomy
Massey University
Palmerston North, New Zealand
Abstract Treatment with 2[[alpha]]-bromoergocriptine mesylate
(CB154) was used to determine the effects on ovine lactogenesis of short-
versus long-term suppression of circulating prolactin (PRL) concentrations in
single- and twin-bearing ewes and whether the effects were associated with
changes in plasma concentrations of progesterone or insulin. Ewes were housed
under constant photoperiod (18 h light:6 h dark) from 3-4 weeks pre-partum
until 8 days post-partum, then grazed outdoors. Ewes were treated daily with
subcutaneous injections of 2 mg CB154 for 20 +/- 1 days pre-partum (CB20
group, n = 10), or for 9 +/- 1 days pre-partum (CB9 group,
n = 10), or with excipient injections for 19 +/- 2 days pre-partum (Control
group, n = 9), and milked daily for the first week, then on Days 14, 21,
and 28 post-partum. CB154 inhibited PRL secretion and delayed lactogenesis with
no consistent effects on plasma progesterone or insulin concentrations. PRL
concentrations were higher (P < 0.05) in CB9 than in CB20 ewes from
14 days pre-partum until 1 day post-partum and plasma PRL concentrations in the
two groups converged as they approached parturition (P < 0.01). There
was no significant treatment group by pregnancy rank interaction for
circulating PRL concentrations. Although the delay in lactogenesis did not
differ between CB20 and CB9 ewes, CB154 treatment was more effective in
reducing milk yield in twin-bearing than in single-bearing ewes when used for
20 days, but not for 9 days, pre-partum (P < 0.05). These results
indicate that, during the period 20-10 days pre-partum, CB154 treatment had a
marked effect on milk yield in twin- but not single-bearing ewes which can not
be explained by corresponding effects on plasma PRL, progesterone, or insulin
concentrations.
Keywords prolactin; progesterone; insulin; bromocriptine;
sheep; lactogenesis
New Zealand Journal of Agricultural Research, 1997, Vol. 40: 249-259
0028-8233/97/4002-0249 $7.00/0 (c) The Royal Society of New Zealand
1997
PDF file of entire paper: medium quality (903K); (scanned from paper original: notes about this process)
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