אסיף מאגר המחקר החקלאי

The effect of GnRH administered to dairy cows during oestrus on plasma LH and conception in relation to the time of treatment and insemination

Year:

1991

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Volume :

24

Co-Authors:

Rosenberg, M., Institute of Animal Science, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel
Chun, S.Y., Institute of Animal Science, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel
Kaim, M., Institute of Animal Science, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel
Herz, Z., Institute of Animal Science, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel
Folman, Y., Institute of Animal Science, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel

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Abstract:

The ocstrous cycles of 480 dairy cows were synchronized with prostaglandin F2α and progesterone coils during two consecutive years. Within 20 h of oestrus detection, cows were treated with saline, 100 or 250 μg GnRH, or 10 μg of the GnRH analogue Buserelin. When GnRH was administered before the spontaneous preovulatory LH surge, the height of the LH surge was 25.8 ± 2.1 ng ml-1 compared to 9.7 ± 0.7 ng ml-1 when GnRH was administered after the spontaneous surge and compared to 12.0 ± 0.8 ng ml-1 in saline-treated cows (P < 0.001). During experimental periods when first-insemination conception rates of control primiparous and multiparous cows were 30.0% and 33.3%, respectively, GnRH administered within 3 h of oestrus detection increased conception to 64.3% in primiparous cows (P < 0.005) and 56.1% in multiparous cows (P < 0.05). When GnRH was administered 16-20 h after oestrus detection or during experimental periods when conception of control animals was higher than 50%, treatment with GnRH had no effect on conception. Multiparous cows which required two to four inseminations and were treated with GnRH within 3 h of oestrus detection had a conception rate of 28.6% when inseminated within 3 h of oestrus detection compared to 67.9% when inseminated 4-30 h following oestrus detection (P < 0.05). Primiparous cows had a significantly higher conception rate than multiparous cows among GnRH-treated animals (65.1% vs. 50.4%) but not among control animals (53.0% vs. 46.2%). © 1991.

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