Some Effects of Using Progesterone and Gonadotrophin Releasing
Hormone on the Reproductive Performance of Inseminated Cows
V.K. Taufa, K.L. MacMillan, A.M. Day, M.J. Ashcroft and S.Morgan
Dairying Research Corporation, Private Bag 3123, Hamilton
Proceedings of the New Zealand Society of Animal Production. 1998,
58: 92-94
The administration of progesterone (P4) within 3 days following
insemination can reduce pregnancy rates. In contrast, an injection of
gonadotrophin releasing hormone (GnRH) at about 12 or 13 days after
insemination can increase them by around 10%. This field trial tested
the hypothesis that the negative effects reported for the P4 treatment
on fertility could be eliminated by strategically injecting GnRH to
convert the two ovarian follicle waves per cycle created by using P4,
into three wave ones, with increased fertility. A total of 830 cows in
13 dairy herds received comparative treatments involving: (i) the
insertion of a P4 intravaginal device 2 or 3 days after first
insemination (1st insem.) for 10 days, with an injection of 10 mg of
GnRH at device removal (P4 + GnRH); (ii) the same GnRH treatment but
without P4 pre-treatment (GnRH); and, (iii) no post-insemination
intervention (Control). Pregnancy status and conception date were
confirmed by rectal palpation of uterine contents Calving data were
recovered from 10 herds to monitor gestation length, dystocia and calf
birth weight. The conception rates to 1st insem. were highest for the
255 cows treated with GnRH (64%; p = 0.05), but similar in the other two
groups of 273 and 302 cows (57%). Second insemination results were not
affected by the treatments; neither were final pregnancy rates. Birth
weights were higher for bull than heifer calves (36.9 vs 33.0kg;
p<0.01), but were not affected by treatment. The results of this trial
showed that the P4 + GnRH treatment did have normal fertility and that
GnRH injected 12 or 13 days after first insemination could increase
conception rates.
Keywords: NZSAPAB;
Gonadotrophin releasing hormone, progesterone, pregnancy.
Last Updated 12-09-1998
