|کد مقاله||کد نشریه||سال انتشار||مقاله انگلیسی||ترجمه فارسی||نسخه تمام متن|
|5523015||1401360||2018||6 صفحه PDF||ندارد||دانلود کنید|
â¢Ovulation occurred mostly between 28 and 30Â h after GnRH injection.â¢Cows in the Saline group ovulated later than 36Â h post-injection.â¢Ovulation rate within 48Â h of GnRH injection tended to be increased (93.3%).â¢Cows showed complete luteolysis following two low doses of PGF2Î±.â¢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 9â10 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 0â3 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