|کد مقاله||کد نشریه||سال انتشار||مقاله انگلیسی||ترجمه فارسی||نسخه تمام متن|
|5523015||1546064||2018||6 صفحه PDF||سفارش دهید||دانلود کنید|
- Ovulation occurred mostly between 28 and 30Â h after GnRH injection.
- Cows in the Saline group ovulated later than 36Â h post-injection.
- Ovulation rate within 48Â h of GnRH injection tended to be increased (93.3%).
- Cows showed complete luteolysis following two low doses of PGF2Î±.
- This protocol was an effective alternative to TAI in cows.
This study investigated the effect of gonadotropin-releasing hormone (GnRH) on ovulatory response after complete luteolysis induced by two low doses of prostaglandin (PG)F2Î± in lactating dairy cows. Cows (nÂ =Â 18) ranging between 45 and 65 days in milk were recruited for synchronization by a modified Ovsynch-48 protocol (GnRH-7 days-375Â Î¼g PGF2Î±-1 day-250Â Î¼g of PGF2Î±-1 day-GnRH) over a total of 23 estrous cycles. Synchronized cows (nÂ =Â 16) were randomly assigned to GnRH and Saline groups in stage 1 of the experiment after 9-10 days of ovulation in synchronization. On days 0 and 1 (day 0Â =Â first PGF2Î± administration), cows were treated with 375 and 250Â Î¼g PGF2Î±, respectively. On day 2, cows in the GnRH and Saline groups were administered 250Â Î¼g GnRH or 2.5Â mL of 0.9% saline, respectively. Serum progesterone (P4) levels were measured and changes in the corpus luteum (CL) were ultrasonically monitored daily from day 0-3 to assess complete luteolysis. Preovulatory follicle diameter and ovulatory response were evaluated by ultrasonography. In stage 2, cows were treated in a manner converse to that in stage 1. The synchronization rate was 69.6% (16/23). In stages 1 and 2, cows showed complete luteolysis with P4 concentration <1Â ng/mL or remaining CL area <50%. Average ovulation time was 29.3Â Â±Â 0.5Â h, which mostly occurred between 28 and 30Â h after GnRH injection. However, all cows in the Saline group ovulated later than 36Â h post-injection, with an average time of 52.7Â Â±Â 8.6Â h. There was no difference in preovulatory follicle diameter between the two groups (16.8Â Â±Â 0.5 and 17.3Â Â±Â 0.5Â mm for GnRH and saline groups, respectively). Although ovulation rate was not correlated with treatment, the rate within 48Â h of GnRH injection (93.3%) tended to be higher compared with that in the Saline group (60.0%). Thus, GnRH administration increased ovulation rate following complete luteolysis induced by two low doses of PGF2Î±. These results indicate that this simple protocol for dairy cows is an effective alternative to timed artificial insemination programs in the field.
Journal: Theriogenology - Volume 105, 1 January 2018, Pages 45-50