[Use of gonadorelin[6-D-Phe] at day 0 or 12 after insemination to increase the conception rate in a large dairy herd in Saxony/Germany].
OBJECTIVE
To increase conception rates in lactating dairy cows by the application of a gonadotropin-releasing-hormone (GnRH)-agonist after insemination.


METHODS
A total of 3125 inseminations of 1634 cows were included in this study. The animals were randomized into three groups at the time of insemination (day 0) using the final numeral of the ear-tag number: The cows of the GnRH0 group were treated using 100 μg gonadorelin[6-D-Phe] intramuscularly immediately after insemination (day 0), while those of the GnRH12 group were treated similarly at day 12. The cows of the control group received no hormonal treatment after insemination. An examination for pregnancy was performed at day 28 using transrectal ultrasonography. Analysis of the data sets was conducted for the number of inseminations (NI) 1-4 and for the last observed insemination of the respective cow during the experimental period, respectively. In a second step, statistical analysis was performed for the first service of cows with a lactation number of 1 versus > 1, with emphasis on the daily milk yield. In addition, a metritis diagnosed after the previous parturition was investigated as a possible factor influencing NI 1.


RESULTS
Pregnancy risk at day 28 was decreased for NI 2 (n = 792) in the GnRH0 group compared to the control group (odds ratio [OR] = 0.69; 95% confidence interval [CI95] = 0.5-1.0; p = 0.04). A similar observation was found for NI 3 (n = 495) for the GnRH12 group (OR = 0.54; CI95 = 0.3-0.9; p = 0.01). In contrast, the pregnancy risk was increased for cows with a lactation number ≥ 2 and with a daily milk yield ≥ 42.5 kg (7-day-mean at day 0) at the first service (n = 364) by treatment with gonadorelin immediately after insemination (OR = 2.0; CI95 = 1.2-3.4; p = 0.01). No significant differences in the pregnancy risk were observed for the remaining analysed classes.


CONCLUSIONS
An increased conception rate was only achieved for the first service of high-yield dairy cows (lactation number ≥ 2) by gonadorelin treatment at day 0. Presumably, the higher incidence of delayed ovulations in this group was treated successfully by gona- dorelin administration.
Dr. Markus Freick, Straße der Jugend 68, 09306 Zettlitz OT Methau, E-Mail: mfreick@gmx.de.
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M
Freick
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O
Weber
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O
Passarge
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Neubert
D000818:Animals; D002417:Cattle / Q000502:physiology*; D003612:Dairying / Q000379:methods*; D005260:Female; D005306:Fertilization / Q000187:drug effects*; D005858:Germany; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000031:analogs & derivatives*; D007315:Insemination, Artificial / Q000662:veterinary*; D007774:Lactation / Q000187:drug effects; D011247:Pregnancy; D011897:Random Allocation
C523569:gonadorelin(6-D-Phe); D007987:Gonadotropin-Releasing Hormone
Dairy cows; GnRH; fertility; pregnancy risk; progesterone