Factors influencing upfront single-and multiple-ovulation incidence, progesterone, and luteolysis before a timed insemination resynchronization protocol.

Our objectives were to determine relationships among factors influencing responses to the first GnRH injection in a timed artificial insemination (TAI) protocol and subsequent fertility after altering timing of the second GnRH injection and AI relative to PGF(2alpha) injection. Replacement heifers (n = 86) and 613 lactating cows previously inseminated were diagnosed not pregnant to form 77 breeding clusters spanning 36 mo. At not-pregnant diagnosis (d 0), females received 100 mug of GnRH, and then 7 d later, they received 25 mg of PGF(2alpha). Females in 2 treatments received GnRH 48 h (G48) after PGF(2alpha) injection and TAI at the time of the second GnRH injection (G48 + TAI48) or 24 h later (G48 + TAI72). Females in the third treatment received GnRH 72 h after PGF(2alpha) when inseminated (G72 + TAI72). Neither timing of GnRH nor time of AI altered TAI pregnancy rates (average of 20.4%). Ovaries of females in 65 clusters were scanned on d 0 (first GnRH injection) and 7 d later (PGF(2alpha) injection). Ovarian structures were mapped and ovulation in response to the first GnRH injection was evaluated on d 7. When estrus was detected before scheduled TAI, females were inseminated; otherwise, TAI conception of remaining females was based on timing of GnRH and AI in 3 treatments. On d 7, 1 or more new corpora lutea (CL) were detected in 43% of females and their pregnancy rate was subsequently greater (28 vs. 18%) than those not ovulating. Follicle diameters on d 0 did not differ between females that did (11.9 +/- 0.3 mm) and did not (11.8 +/- 0.4 mm) subsequently ovulate in response to GnRH. Follicle diameter and number of follicles >/=5 mm increased with increasing lactation number, but decreased with increasing number of CL. Diameter of follicles in which more than 1 follicle ovulated decreased linearly from that in which only 1 follicle ovulated. Incidence of ovulation increased with increasing lactation number and total number of follicles >/=5 mm, but decreased with increasing number of CL. Incidence of multiple ovulations (15%) was greater in females having more follicles >/=5 mm and in those in early diestrus. Multiple ovulation did not occur in heifers, but was decreased in cows having more than 1 CL. In cows having more than 1 CL, luteal regression was reduced by 5.6 percentage units compared with those having 1 CL. In a TAI protocol, pregnancy rate was greater for females in early diestrus compared with females in other stages of the cycle, in those that ovulated after the first GnRH injection, in those having luteolysis, and in those inseminated during nonsummer months.

Stevenson JS ，Portaluppi MA ，Tenhouse DE 《-》

Pregnancy rates in lactating dairy cows after presynchronization of estrous cycles and variations of the Ovsynch protocol.

Our objectives were to determine pregnancy rates after altering times of the second GnRH injection, insemination, or both in a combined Presynch + Ovsynch protocol, to accommodate once-daily lockup of dairy cows. Lactating dairy cows (n = 665) from 2 dairy herds in northeastern Kansas were studied. Cows ranged from 24 to 44 d in milk (DIM) at the start of the Pre-synch protocol, which consisted of 2 injections of PGF(2alpha) 14 d apart, with the second injection given 12 d before initiating the Ovsynch protocol. Cows were blocked by lactation number and assigned randomly to 3 treatments consisting of variations of the Ovsynch protocol. Cows in 2 treatments received injections of GnRH 7 d before and 48 h (G48) after the PGF(2alpha) injection. Timed AI (TAI) was conducted at the time of the second GnRH injection (G48 + TAI48) or 24 h later (G48 + TAI72). Cows in the third treatment received the injections of GnRH 7 d before and at 72 h after PGF(2alpha) and were inseminated at the time of the second GnRH injection (G72 + TAI72). Pregnancy was diagnosed weekly by palpation per rectum of uterine contents on d 40 or 41 after TAI. Pregnancy rates differed between herds, but they were consistently greater for G72 + TAI72 than for G48 + TAI48 and G72 + TAI72. Subsequent calving rates were consistent with differences in initial TAI pregnancy rates. Pregnancy loss was least for cows on the G72 + TAI72 treatment. Body condition scores (BCS) ranged from 1.0 to 4.0 when assessed on Monday of the breeding week. An interaction of BCS and herd was detected in which cows in herd 1 having poorer BCS (<2.25) had greater pregnancy rates than cows of greater BCS (>/=2.25), whereas the reverse was true in herd 2 in which overall pregnancy rates were greater. We concluded that inseminating at 48 or 72 h after PGF(2alpha), when GnRH was administered at 48 h after PGF(2alpha), produced fewer pregnancies than inseminating and injecting GnRH at 72 h after PGF(2alpha) for cows whose estrous cycles were synchronized before initiating this variant of the Ovsynch protocol.

Portaluppi MA ，Stevenson JS 《JOURNAL OF DAIRY SCIENCE》

Evaluation of human chorionic gonadotropin as a replacement for gonadotropin-releasing hormone in ovulation-synchronization protocols before fixed timed artificial insemination in beef cattle.

Two experiments were conducted during 2 yr to evaluate differences in ovulation potential and fertility in response to GnRH or hCG. In Exp. 1, 46 beef cows were given 100 microg of GnRH or 500, 1,000, 2,000, or 3,000 IU of hCG. Ovulation incidence was not different between GnRH and any of the hCG doses, indicating that ovulatory capacity of at least 500 IU of hCG was equivalent to GnRH. In Exp. 2, beef cows (n = 676) at 6 locations were assigned randomly to a 2 x 3 factorial arrangement of treatments. Main effects were: 1) pre-timed AI (TAI) treatment (GnRH or hCG) and 2) post-TAI treatment (saline, GnRH, or hCG) to initiate resynchronization of ovulation in previously inseminated cattle. Blood samples were collected (d -21 and -10) to determine progesterone concentrations and assess cyclicity. Cattle were treated with a progesterone insert on d -10 and with 100 microg of GnRH or 1,000 IU of hCG. A PGF(2alpha) injection was given at insert removal on d -3. Cows were inseminated 62 h (d 0) after insert removal. On d 26 after first TAI, cows of unknown pregnancy status were treated with saline, GnRH, or hCG to initiate a CO-Synch protocol. Pregnancy was diagnosed 33 d after first TAI to determine pregnancies per AI (P/AI). Nonpregnant cows at 6 locations in yr 1 and 1 location in yr 2 were given PGF(2alpha) and inseminated 56 h later, concurrent with a GnRH injection. Five weeks later, pregnancy diagnosis was conducted to determine pregnancy loss after first TAI and pregnancy outcome of the second TAI. Injection of pre-TAI hCG reduced (P < 0.001) P/AI compared with GnRH, with a greater reduction in cycling cows. Post-TAI treatments had no negative effect on P/AI resulting from the first TAI. Serum progesterone was greater (P = 0.06) 7 d after pre-TAI hCG than after GnRH and greater (P < 0.05) after post-TAI hCG on d 26 compared with saline 7 d after treatment in association with greater frequency of multiple corpora lutea. Compared with saline, injections of post-TAI GnRH and hCG did not increase second insemination P/AI, and inconsistent results were detected among locations. Use of hCG in lieu of GnRH is contraindicated in a CO-Synch + progesterone insert protocol. Compared with a breeding season having only 1 TAI and longer exposure to cleanup bulls, total breeding season pregnancy rate was reduced by one-third, subsequent calving distribution was altered, and 50% more AI-sired calves were obtained by applying 2 TAI during the breeding season.

Burns MG ，Buttrey BS ，Dobbins CA ，Martel CA ，Olson KC ，Lamb GC ，Stevenson JS ... -  《-》

Progesterone, follicular, and estrual responses to progesterone-based estrus and ovulation synchronization protocols at five stages of the estrous cycle.

The objective was to monitor changes in ovarian status in heifers exposed to a progesterone insert with or without concurrent GnRH injection. Estrus was manipulated in 283 heifers (31 breeding clusters) by administering GnRH, progesterone, and PGF(2alpha) at 5 stages of the estrous cycle. Estrus was presynchronized with a progesterone insert (CIDR) for 7 d before PGF(2alpha) was administered 24 h before insert removal. Successive clusters of heifers were assigned to treatments (2 heifers per treatment) on cycle d 2, 5, 10, 15, and 18. Treatments consisted of a progesterone insert (d 0) for 7 d plus: 1) PGF(2alpha) on d 6, 24 h before insert removal (early PGF); 2) GnRH on d 0 + early PGF(2alpha) (GnRH + early PGF); 3) PGF(2alpha) at insert removal (late PGF); and 4) GnRH on d 0 + late PGF (GnRH + late PGF). Controls received GnRH on d 0 and PGF(2alpha) on d 7. Ovaries were scanned by transrectal ultrasonography on d 0, 2, 7, 9, and 11 to assess follicle diameters and ovulation. Blood was collected on d 0, 2, 6, 7, 8, and 9 to quantify serum concentrations of progesterone. Insemination occurred after detected estrus or by timed artificial insemination (TAI) at 64 h after insert removal. Only 25% of 141 GnRH-treated heifers ovulated by d 2; twice as many ovulated when treatment was initiated on d 5 (46.4%) than on other cycle days (20.3%). Diameters of the largest follicle exposed to GnRH on d 0, 2, 7, or 9 did not differ regardless of whether ovulation occurred. Small treatment and stage of cycle differences in diameter of the largest follicle were detected on d 2, 7, and 9. Compared with controls, progesterone concentration was greater in all progesterone-treated heifers on d 2 and 6. Early- vs. late-PGF treatment resulted in less progesterone on d 7 and 8. Pregnancies per AI were less after TAI (44%) than after detected estrus (56%) and were less in controls than in all progesterone treatments. Heifers in which treatments were initiated on d 10 of the cycle had the most consistent (estrus vs. TAI) pregnancies per AI (65.4%) compared with other cycle days. Compared with controls, more progesterone-treated heifers ovulated by 96 h after insert removal. Application of the progesterone insert reduced variance of the interval to estrus after insert removal (or PGF(2alpha) injection in controls) by 1.6-fold compared with controls. These results do not support the use of GnRH in a progesterone-based synchronization protocol.

Stevenson JS 《-》

Effect of pretreatment with prostaglandin F2alpha before resynchronization of ovulation on fertility of lactating dairy cows.

Our objective was to assess the effect of pretreatment with PGF(2alpha) 12 d before initiation of a protocol for resynchronization of ovulation (Resynch) using an Ovsynch protocol. Lactating Holstein cows diagnosed not pregnant 31 d after a timed artificial insemination (TAI) were randomly assigned to initiate the Resynch protocol 32 d after TAI (n = 255; RES), or receive 25 mg of PGF(2alpha) 34 d after TAI and initiate the Resynch protocol 12 d later at 46 d after TAI (n = 272; PGF+RES). Within each treatment, a subset of cows were examined using transrectal ultrasonography to determine ovulatory response to the first GnRH injection of the Resynch protocols or a blood sample was collected to determine serum progesterone (P(4)) at initiation of the Resynch protocol, or both. Overall, PGF+RES cows had more pregnancies per artificial insemination (P/AI) than RES cows 66 d after TAI (35.2 vs. 25.6%), whereas pregnancy loss from 31 to 66 d after TAI was greater for RES than PGF+RES cows (17.1 vs. 7.6%). Although P/AI was greater for cows with high (>/=1.0 ng/mL) vs. low (<1.0 ng/mL) P(4) at the first GnRH injection of the Resynch protocols, treatment did not affect the proportion of cows with low P(4) at the first GnRH injection of the Resynch protocols. Overall, no effect of treatment on ovulatory response to the first GnRH injection of the Resynch protocols was detected. We conclude that pretreatment with PGF(2alpha) 12 d before initiation of the Resynch protocol increased P/AI 66 d after TAI for cows with serum P(4) concentration >1.0 ng/mL at the first GnRH injection of the Resynch protocol and decreased pregnancy loss from 31 to 66 d after TAI. This modified resynchronization protocol may be a useful strategy for reproductive management of lactating dairy cows.

Silva E ，Sterry RA ，Kolb D ，Wiltbank MC ，Fricke PM ... -  《-》