Sufficiency of progesterone limits conception rate in dairy cows. This study evaluates the effect of gonadotropin-releasing hormone on induction of accessory corpus luteum, progesterone concentrations and pregnancy in dairy cows. The hormone (0.05 mg) was administrated intramuscularly to cows with one corpus luteum on day 5-7 (Group E1, n = 57) or 11-13 (Group E2, n = 40) after insemination; control groups C1 (n = 54) and C2 (n = 41) were not treated. Detection of pregnancy by ultrasound examination and measurement of serum progesterone concentration was performed on day 25-39 and around day 90 after insemination. The occurrences of two corpora lutea in groups E1 and E2 versus C1 and C2 were 43.9% and 33.5% vs. 3.7% and 9.8% (P < 0.001). Progesterone concentrations were 5.9 ± 2.92 ng/ml and 7.8 ± 2.35 ng/ml in untreated and treated cows (P = 0.016), respectively. Conception rates in groups E1 and E2 were 100% and 86.7% in cows bearing two corpora lutea, and only 16.7% and 38.9% in cows bearing one corpus luteum (P < 0.01); similarly as in groups E1 and E2 compared to groups C1 and C2 (49.1% and 50% vs. 50% and 31.7%). Pregnancy rates around day 90 in groups E1 and E2 compared to groups C1 and C2 were 45.6% and 45% vs. 42.6% and 26.8%, respectively. Administration of gonadotropin-releasing hormone on day 5-7 or 11-13 after insemination was efficient to induce accessory corpus luteum and increase the concentration of serum progesterone but had no effect on the conception rate.
Doležel R., Chambert C., Musilová D., Čech S., Páleník T. (2017): Induction of accessory corpus luteum by gonadorelin in relation to the time of treatment and the follicle size in inseminated cows. Czech J. Anim. Sci., 62,[195][196][197][198][199][200] This study evaluated the occurrence of two corpora lutea (CL) and the pregnancy rate in cows treated with gonadorelin on days 5, 6 or 7 after insemination in relation to the day of treatment and the size of the largest follicle on the ovaries at the time of treatment. Cows bearing one CL on days 5 (n = 40), 6 (n = 48), and 7 (n = 47) after insemination with defined size of the largest follicle on the ovaries (small ≤ 9 mm, n = 34; medium 10-14 mm, n = 59; large 15-20 mm, n = 42) were included in the study. Gonadorelin was administered after examination (day 0) and ultrasonographic examination was repeated on days 14, 28, and around day 90. The occurrence of 2 CL vs 1 CL was higher in pregnant cows on day 14 as well as on day 28 (86 vs 14% and 82.5 vs 14%, n = 57). Pregnancy rates on day 28 and around day 90 were higher in cows bearing 2 CL (n = 57) vs cows bearing 1 CL (n = 54) (82.5 vs 18.5% and 79.0 vs 18.5%, P < 0.001). The occurrence of 2 CL on day 28 was higher in cows treated on day 5 compared to cows treated on day 6 or 7 after insemination (60.0 vs 33.3 or 36.2%, P < 0.05). No significant differences in the number of CL and pregnancy rate were found in relation to follicle size at the time of treatment. Our results showed the higher efficiency of accessory CL induction by gonadorelin administration in cows treated on day 5 vs those treated on day 6 or 7 post insemination, however efficiency of the treatment was not influenced by the size of the largest follicle on the ovaries.
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