Induction of early post-calving ovulation and oestrus in suckled beef
cows
W.H. McMillan, D.R.H. Hall, A.P. Oakley
Dairy and Beef Division, AgResearch Ruakura, Private Bag 3123,
Hamilton, New Zealand
Proceedings of the New Zealand Society of Animal Production. 1995,
55: 261-264
The aim of this study was to compare the efficacy of exogenous
progesterone, either without or with a single injection of gonadotrophin
releasing hormone (GnRH), at initiating early post-calving ovulatory and
oestrous activity. Six days (d)after the first post-partum follicle had attained
dominance cows were allocated to either an untreated control group; treated
with a progesterone-impregnated CIDR’ device for 5 d; or treated with a
progesterone-impregnated CIDR’ device for 5 d plus 250 mg GnRH given
30 h later. The mean (± s.e.) interval from calving to first ovulation was
longer (P<0.01) in untreated cows (47 ± 6) compared with CIDR-treated
cows either with GnRH (32 ± 4) or without GnRH (27 ± 1). Similarly, the
interval from calving to first oestrus was longer in untreated cows, 73 ± 10
days compared with 57 ± 6 and 36 ± 6 respectively, (P<0.01). These result
demonstrate that the interval to first ovulation and to first oestrus can be
reduced in suckled cows.
Keywords: NZSAPAB;
beef cow; ovary; dominant follicle; post-partum; anoestrus;
progesterone; GnRH; CIDR
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Last Updated 25-01-1997
