Comparison of the 7 & 7 Synch protocol and the 7-day CO-Synch + CIDR protocol among recipient beef cows in an embryo transfer program.

An experiment was designed to evaluate the effectiveness of the recently developed 7 & 7 Synch protocol to synchronize estrus among recipients prior to embryo transfer (ET). Postpartum beef cows (n = 1358) across thirteen locations were assigned to either the 7-d CO-Synch + CIDR protocol or the 7 & 7 Synch protocol prior to ET. Cows were preassigned to balanced treatments within location based on age and days postpartum, with body condition score recorded at ET. Cows assigned to the 7-d CO-Synch + CIDR protocol were administered gonadotropin-releasing hormone (GnRH; 100 µg gonadorelin acetate) on Day 7, an intravaginal controlled internal drug release (CIDR; 1.38 g progesterone) from Day 7 to Day 14, and prostaglandin F2α (PGF2α; 25 mg dinoprost tromethamine) coincident with CIDR removal on Day 14. Cows assigned to the 7 & 7 Synch protocol were administered PGF2α (25 mg dinoprost tromethamine) coincident with CIDR insertion on Day 0, GnRH (100 µg gonadorelin acetate) on Day 7, and PGF2α (25 mg dinoprost tromethamine) coincident with CIDR removal on Day 14. Cows were observed for visible signs of estrus, with GnRH (100 µg gonadorelin acetate) administered to cows failing to express estrus during the detection period. Embryo transfer was performed approximately seven days after estrus or GnRH administration. Presence of corpora lutea (CL) was determined via transrectal palpation by a single veterinarian blinded to treatment, and embryos were transferred only to cows with palpable CL. Embryo transfer was performed using either fresh or frozen embryos, with embryo stage and grade recorded for each recipient. The proportion of cows expressing estrus was increased (P < 0.0001) among cows assigned to the 7 & 7 Synch protocol (86% [529/615] vs 76% [488/640]). The proportion of cows expressing estrus and presenting with palpable CL at ET was greater (P < 0.0001) among cows following treatment with the 7 & 7 Synch protocol compared to the 7-d CO-Synch + CIDR protocol (76% [466/615] vs 65% [418/640]). Consequently, the proportion pregnant to ET was greater (P < 0.03) following the 7 & 7 Synch protocol (40% [263/653]) compared to the 7-d CO-Synch + CIDR protocol (34% [228/664]). In summary, the 7 & 7 Synch protocol involving administration of PGF2α and treatment with a CIDR for 7 days prior to GnRH improved the likelihood of estrus expression in recipients, increased the proportion of cows eligible to receive an embryo, which resulted in a greater pregnancy rate to ET.

Comparison of long-term progestin-based protocols to synchronize estrus prior to natural service or fixed-time artificial insemination in Bos indicus-influenced beef heifers.

This experiment was designed to evaluate breeding strategies involving natural service or fixed-time artificial insemination (FTAI) in Bos indicus-influenced beef heifers (n = 1456) when there were field-type management conditions. Body weights and reproductive tract scores (RTS; Scale 1-5) were obtained for heifers before assignment to one of five treatments: 1) Non-synchronized control exposed for natural service (NS), n = 299; 2) melengestrol acetate + natural service (MGA + NS; 0.5 mg/heifer/d), n = 295; 3) 14-d controlled internal drug release insert + natural service (CIDR + NS), n = 289; 4) 14-d MGA-prostaglandin F2α (PG) + FTAI, n = 295; or 5) 14-d CIDR-PG + FTAI, n = 278. Fertile bulls were placed in pastures with heifers of the three NS treatment groups for a 65-day period which began 10 days after progestin treatments (MGA or CIDR) ended. Heifers in FTAI treatment groups were administered PG (25 mg, IM) 16 days after CIDR removal or 19 days following MGA withdrawal, respectively, and FTAI was performed at 66 (CIDR-PG) or 72 h (MGA-PG) after PG. Gonadotropin-releasing hormone (GnRH; 100 µg, i.m.) was administered at FTAI. Pregnancy status was determined at the end of a 65-day breeding period. Pregnancy rates on Days 21 and 65 of the breeding period differed among treatment groups based on pre-treatment pubertal status (P ≤ 0.02) and body weight (P ≤ 0.05) but did not differ by group. These data highlight the need for continued research efforts to improve reproductive management of Bos indicus-influenced females.

Altering duration of the presynchronization period in a long-term progestin-based estrus synchronization protocol for timed artificial insemination of beef heifers.

An experiment was designed to evaluate the effect of extending duration of the presynchronization treatment in a long-term progestin-based estrus synchronization protocol. Heifers were assigned to either an 18 d (Day 0-18) or 14 d (Day 4 to Day 18) CIDR® treatment (1.38 g progesterone controlled internal drug release insert; Zoetis, Madison, NJ), with prostaglandin F2α (PG; 250 µg im cloprostenol sodium) administered 16 d after CIDR® removal (Day 34). Heifers at two locations (location one, n = 193; location two, n = 649) were assigned to treatment based on reproductive tract score (RTS; Scale 1-5) and body weight. Heifers that were assigned RTS 1 were not retained for the trial (n = 6). Estrus detection aids (Estrotect®) were applied at PG. Split-time artificial insemination (STAI) was utilized and AI performed based on expression of estrus at 66 h. Expression of estrus was defined as removal of ≥50% of the grey coating from the Estrotect® patch. Heifers that expressed estrus at 66 h were inseminated then and heifers that had not expressed estrus were inseminated at 90 h. Only heifers that failed to express estrus by 90 h received gonadotropin-releasing hormone (GnRH; 100 µg im gonadorelin acetate) at the time of AI. At location one, blood samples were collected at PG and AI (66 h or 90 h) from all heifers to determine E2 concentration by radioimmunoassay, and transrectal ovarian ultrasound was performed to detail ovarian structures on a subset of heifers (n = 73) at both time points. The proportion of heifers expressing estrus did not differ between treatments, either by 66 h (60%) or in total by 90 h (84%) after PG. Pregnancy rate to STAI did not differ between treatments (P = 0.3; 52%, 14-d CIDR®-PG; 50%, 18-d CIDR®-PG), or at the end of the 60 d breeding season (P = 0.2; 86%, 14-d CIDR®-PG; 82%, 18-d CIDR®-PG). No differences were detected in mean diameter of the dominant follicle at PG (P = 0.6; 10.9 ±â€¯0.4 mm, 14-d CIDR®-PG; 11.0 ±â€¯0.4 mm, 18-d CIDR®-PG) or at STAI (P = 0.3; 12.6 ±â€¯0.4 mm, 14-d CIDR®-PG; 13.2 ±â€¯0.4 mm, 18-d CIDR®-PG), nor were any differences observed between treatments in concentrations of E2 at PG (P = 0.8; 1.1 ±â€¯0.19 pg/ml, 14-d CIDR®-PG; 1.1 ±â€¯0.19 pg/ml, 18-d CIDR®-PG) or STAI (P = 0.6; 3.8 ±â€¯0.19 pg/ml, 14-d CIDR®-PG; 3.6 ±â€¯0.19 pg/ml, 18-d CIDR®-PG). These data indicate that duration of CIDR® treatment can be extended from 14 to 18 d, thus providing flexibility in scheduling without compromising reproductive outcomes.

Evaluation of split-time artificial insemination following administration of a long or short-term progestin-based estrus synchronization protocol in beef heifers.

Fixed-time and split-time AI were compared following the melengestrol acetate (MGA®) prostaglandin F2α (Experiment 1) and 7-d CO-Synch + controlled internal drug release (CIDR®) protocols (Experiment 2). Heifers in Experiments 1 (n = 524) and 2 (n = 456) were assigned within pen to balanced treatments based on weight and reproductive tract score (RTS; Scale 1-5). In Experiment 1, MGA® (0.5 mg∙animal-1∙d-1) was fed for 14 d, and prostaglandin F2α (PG; 250 µg im cloprostenol sodium) was administered 19 d after MGA® withdrawal. In Experiment 2, gonadotropin-releasing hormone (GnRH; 100 µg gonadorelin acetate) was administered coincident with CIDR® (1.38 g progesterone [P4]) insertion. Inserts were removed after 7 d, and PG (250 µg im cloprostenol sodium) was administered at CIDR® removal. In both experiments, estrus detection aids (Estrotect®) were applied at the time of PG administration. Estrous status was recorded at FTAI or STAI. Estrus was defined as removal of ≥ 50% of the grey coating from the Estrotect® patch. Heifers assigned to FTAI treatments received GnRH and were artificially inseminated at the standard time for FTAI for each protocol: 72 or 54 h after PG administration for the MGA-PG or 7-d CO-Synch + CIDR® protocol, respectively. In the STAI treatments, only heifers that expressed estrus prior to the standard time of FTAI were artificially inseminated at that time. For heifers failing to express estrus, AI was postponed 24 h. Only heifers that failed to exhibit estrus by the delayed time received GnRH concurrent with AI. In both experiments, estrous response prior to the standard time of FTAI did not differ between treatments. Total estrous response was increased (P < 0.01) among heifers assigned to STAI in Experiment 1 (88%, STAI; 72%, FTAI) and 2 (74%, STAI; 47%, FTAI). In Experiment 1, pregnancy rates resulting from AI were greater (P < 0.04) for heifers assigned to STAI compared with FTAI (55% vs 46%, respectively). In Experiment 2, pregnancy rates resulting from AI were similar between treatments (48% and 46%, respectively; P = 0.6). In summary, when compared with FTAI, STAI resulted in greater estrous response following both the MGA®-PG and 7-d CO-Synch + CIDR® protocols. The increased estrous response through use of STAI was associated with a corresponding increase in pregnancy rates to AI following the MGA®-PG protocol; however, a similar improvement in pregnancy rates was not observed following the 7-d CO-Synch + CIDR® protocol.

Evaluation of SexedULTRA 4M™ sex-sorted semen in timed artificial insemination programs for mature beef cows.

An experiment was designed to compare fertility of SexedULTRA 4M™ sex-sorted semen and conventional, non-sex-sorted semen following either fixed-time artificial insemination (FTAI) or split-time artificial insemination (STAI) of mature suckled beef cows. Units of sex-sorted and conventional semen were produced using contemporaneous ejaculates from three commercially available sires. Units of conventional semen were generated with 25.0 × 106 live cells per 0.25 ml straw prior to freezing, and units of sex-sorted semen were generated using the SexedULTRATM Genesis III sorting technology with 4.0 × 106 live cells per 0.25 ml straw prior to freezing. Sex-sorted units were sorted to contain X chromosome-bearing sperm cells at an accuracy level of >90%. Cows (n = 1620) across four herds were treated with the 7-d CO-Synch + CIDR protocol [administration of gonadotropin-releasing hormone (GnRH) and insertion of a progesterone insert (CIDR) on Day -10, followed by administration of prostaglandin F2α (PG) and removal of CIDR inserts on Day -3]. Cows were preassigned based on age, body condition score, and days postpartum to one of the following four treatments: FTAI with SexedULTRA 4M™ sex-sorted semen, FTAI with conventional semen, STAI with SexedULTRA 4M™ sex-sorted semen, or STAI with conventional semen. On Day -3, estrus detection aids (Estrotect®) were applied. For cows in FTAI treatments, AI was performed on Day 0 at 66 h after PG administration and CIDR removal, and 100 µg GnRH was administered concurrent with AI. For cows in STAI treatments, AI was performed on either Day 0 or 1, at 66 or 90 h after PG administration and CIDR removal, based on timing of estrus expression. On Day 1 at 90 h after PG administration and CIDR removal, 100 µg GnRH was administered concurrent with AI to any STAI-treated cows that had failed to express estrus. Pregnancy rates to AI were affected (P = 0.04) by the interaction of bull and semen type. Greater pregnancy rates were obtained with conventional semen versus SexedULTRA 4M™ sex-sorted semen when using semen from Bull A (64% [176/277] versus 36% [100/278]; P < 0.0001) and Bull B (72% [200/277] versus 57% [156/276]; P < 0.01), whereas pregnancy rates to AI did not differ between conventional and SexedULTRA 4M™ sex-sorted semen when using semen from Bull C (58% [149/258] versus 52% [131/254]). Pregnancy rates did not differ significantly between cows inseminated using a STAI versus FTAI approach, regardless of whether insemination was performed with conventional semen (65% [265/409] versus 65% [260/403] or SexedULTRA 4M™ sex-sorted semen (50% [200/403] versus 48% [187/405]). However, due to the additional 24 h for potential estrus expression when performing STAI, total estrous response prior to AI was greater (P < 0.001) among cows receiving STAI (84%; 686/812) compared to FTAI (72%; 585/808), and greater pregnancy rates (P < 0.0001) were obtained among cows that expressed estrus prior to AI. In summary, the relative fertility of SexedULTRA 4M™ sex-sorted semen and conventional semen varied across bulls. Although overall pregnancy rates to timed AI did not differ between STAI and FTAI approaches, use of a STAI approach allowed for greater total estrous response prior to AI. Therefore, to achieve acceptable conception rates per unit and service the maximum number of cows with sex-sorted semen, one viable approach may be to use STAI to maximize total estrous response and restrict use of SexedULTRA 4M™ sex-sorted to only those cows expressing estrus.

The 9-d CIDR-PG protocol II: Characterization of endocrine parameters, ovarian dynamics, and pregnancy rates to fixed-time AI following use of long-term CIDR-based estrus synchronization among mature beef cows.

An experiment was designed to evaluate endocrine parameters, ovarian dynamics, and pregnancy rates to fixed-time artificial insemination (FTAI) following the 9-d CIDR-PG protocol in comparison to the 14-d CIDR-PG protocol. While both are long-term protocols using CIDR treatment for presynchronization, the 9-d CIDR-PG protocol differs from the 14-d CIDR-PG protocol in that prostaglandin F2α (PG) is administered at CIDR insertion and removal to facilitate a decreased length of progestin treatment and potentially enhance response to the presynchronization treatment. Estrus was synchronized for 393 mature beef cows across five locations. Treatments were represented in each location, and cows within each location were randomly assigned to one of the two protocols based on age, days postpartum (DPP), and body condition score (BCS). Cows assigned to the 14-d CIDR-PG treatment received a CIDR insert (1.38 g progesterone) on Day 0 with removal of CIDR on Day 14, and 25 mg PG 16 d after CIDR removal on Day 30. Cows assigned the 9-d CIDR-PG treatment received 25 mg PG and a CIDR insert (1.38 g progesterone) on Day 5; 25 mg PG and removal of CIDR on Day 14; and 25 mg PG 16 d after CIDR removal on Day 30. In both treatments, cows received FTAI on Day 33, 72 h after PG. All cows were administered 100 µg gonadotropin-releasing hormone (GnRH) concurrent with insemination. For a subset of animals in each treatment, ovarian ultrasound was performed and blood samples were collected for determination of serum estradiol concentrations at CIDR removal, PG administration, and FTAI. Protocols were compared on the basis of estrous response and pregnancy rate resulting from FTAI. Serum estradiol concentrations, follicle size, and estrous response did not differ based on treatment. However, cows assigned to the 9-d CIDR-PG protocol tended to achieve greater FTAI pregnancy rates than cows assigned to the 14-d CIDR-PG protocol (62% versus 52%; P = 0.07). Across treatments, greater pregnancy rates tended (P = 0.10) to be achieved by cows that expressed estrus prior to FTAI (69% for 9-d CIDR-PG, 58% for 14-d CIDR-PG) than by cows that failed to express estrus (55% for 9-d CIDR-PG, 47% for 14-d CIDR-PG). In summary, the 9-d CIDR-PG protocol is an effective protocol for synchronization of estrus among mature beef cows, and pregnancy rates to FTAI tended to be improved through use of the 9-d CIDR-PG compared to the 14-d CIDR-PG protocol.

Split-time artificial insemination in beef cattle: III. Comparing fixed-time artificial insemination to split-time artificial insemination with delayed administration of GnRH in postpartum cows.

This experiment was designed to compare pregnancy rates in postpartum beef cows following split-time (STAI) or fixed-time (FTAI) artificial insemination. Estrus was synchronized for 671 cows at seven locations following administration of the 7-d CO-Synch + CIDR protocol (100 µg GnRH + CIDR insert [1.38 g progesterone] on d 0; 25 mg prostaglandin F2α [PG] at CIDR removal on d 7). Cows were assigned to treatments that were balanced across locations based on age, body condition score, and days postpartum at the time treatments were initiated. All cows in treatment 1 (n = 333; FTAI) were inseminated at 66 h after PG and GnRH was administered concurrent with insemination regardless of estrus expression. For cows in treatment 2 (n = 338; STAI), inseminations were performed at 66 or 90 h after PG, and estrous status was recorded at these times. Cows in the STAI treatment that exhibited estrus by 66 h were inseminated at that time and did not receive GnRH, whereas AI was delayed 24 h until 90 h after PG for cows that failed to exhibit estrus by 66 h. Gonadotropin-releasing hormone (100 µg) was administered concurrent with AI at 90 h only to cows failing to exhibit estrus. Estrus expression that occurred during the 24 h delay period among cows assigned to the STAI treatment increased the total proportion of cows that expressed estrus prior to insemination (1 = 60%; 2 = 86%; P < 0.001). Pregnancy rates for cows inseminated at 66 h that exhibited estrus did not differ between treatments (1 = 58%; 2 = 58%; P = 0.93); however, pregnancy rates among non-estrous cows at 66 h were improved (1 = 35%; 2 = 51%; P = 0.01) among cows assigned to the STAI treatment when insemination was postponed by 24 h. Consequently, total AI pregnancy rate tended to be higher for cows that received STAI (1 = 49%; 2 = 56%; P = 0.06). In summary, following administration of the 7-d CO-Synch + CIDR protocol, total estrous response increased and pregnancy rates resulting from AI tended to be higher among cows assigned to STAI versus FTAI treatments.

Effective use of SexedULTRA™ sex-sorted semen for timed artificial insemination of beef heifers.

An experiment was designed to evaluate the relative fertility of SexedULTRATM sex-sorted semen compared to conventional, non-sex-sorted semen when used among beef heifers in conjunction with split-time AI following the 14-d CIDR-PG protocol. Units of conventional semen were generated with 25.0 × 106 live cells per 0.5 ml straw prior to freezing, and units of sex-sorted semen were generated using the SexedULTRATM Genesis III sorting technology with 4.0 × 106 live cells per 0.25 ml straw prior to freezing. Sex-sorted units were sorted to contain X chromosome-bearing sperm cells at an accuracy level of >90%. Estrus was synchronized in 851 heifers at four locations using the 14-d CIDR-PG protocol: controlled internal drug release (CIDR) insert (1.38 g progesterone) on Day 0, CIDR removal on Day 14, and administration of prostaglandin F2α (PG; 25 mg im) on Day 30. Estrus detection aids were applied at PG on Day 30 to evaluate estrous response rate, and split-time AI was performed based on estrous response. At 66 h after PG (Day 33), heifers having expressed estrus received timed AI. Heifers failing to express estrus by 66 h received timed AI 24 h later (90 h after PGF2α on Day 34). Heifers failing to express estrus by 90 h were administered gonadotropin-releasing hormone (GnRH; 100 µg im) concurrent with AI. Heifers were preassigned to treatment (insemination with either conventional or SexedULTRATM sex-sorted semen), and treatments were balanced within each location based on source, reproductive tract score, and weight. Heifers were exposed for natural service beginning 14 d after AI for the remainder of a 60 d breeding season. Pregnancy rates to AI across locations tended to be higher (P = 0.09) for heifers inseminated with conventional semen (60%; 257/429) compared to sex-sorted semen (52%; 218/422). Higher pregnancy rates to AI (P < 0.0001) were obtained among heifers that expressed estrus prior to AI than among heifers that failed to express estrus prior to AI at 90 h. Total pregnancy rates at the end of the 60 d breeding season did not differ between heifers that received sex-sorted semen at AI (89%; 376/422) and heifers that received conventional semen at AI (89%; 382/429). In summary, the pregnancy rates observed suggest that SexedULTRATM sex-sorted semen can be used effectively for timed AI of beef heifers when split-time AI is performed following the 14-d CIDR-PG protocol.

Evaluation of the 14-d CIDR-PG and 9-d CIDR-PG protocols for synchronization of estrus in Bos indicus-influenced and Bos taurus beef heifers.

Two long-term, CIDR-based estrus synchronization protocols were evaluated among Bos indicus-influenced and Bos taurus beef heifers. Treatments were evaluated on the basis of estrous response and pregnancy rate resulting from fixed-time artificial insemination (FTAI), and these outcomes were analyzed retrospectively relative to reproductive tract score (RTS; Scale 1-5) at treatment initiation. Estrus was synchronized for 1139 heifers in three locations, and heifers were assigned to one of two treatments within each location based on RTS. Heifers assigned to the 14-d CIDR-PG protocol received a controlled internal drug release (CIDR) insert (1.38 g progesterone) on Day 0, CIDR removal on Day 14, administration of prostaglandin F2α (PG; 25 mg im) on Day 30, and administration of gonadotropin-releasing hormone (GnRH; 100 µg im) concurrent with FTAI on Day 33, 66 h after PG. Heifers assigned to the 9-d CIDR-PG protocol received administration of PG concurrent with CIDR insertion on Day 5, administration of PG concurrent with CIDR removal on Day 14, administration of PG on Day 30, and administration of GnRH concurrent with FTAI on Day 33, 66 h after PG. Estrus detection aids were applied at CIDR removal on Day 14 and at PG on Day 30 to evaluate estrous response rate. Mean RTS differed (P < 0.0001) based on biological type due to higher rates of estrous cyclicity (RTS 4 and 5) among Bos taurus heifers (72%; 416/574) than among Bos indicus-influenced heifers (27%; 150/565). The proportion of heifers expressing estrus following CIDR removal was greater (P = 0.01) among heifers assigned to the 14-d CIDR-PG treatment (88%; 492/559) compared to the 9-d CIDR-PG treatment (83%; 480/580). Estrous response following CIDR removal was also higher (P < 0.0001) among Bos taurus (95%; 547/574) compared to Bos indicus-influenced (75%; 425/565) heifers. Rate of estrous response prior to FTAI did not differ significantly based on treatment but was higher (P < 0.0001) among Bos taurus heifers (60%; 344/574) than among Bos indicus-influenced heifers (45%; 253/565). However, the effect of biological type on estrous response was not significant when RTS was included in the model, as RTS significantly (P < 0.0001) affected the rate of estrous response both at CIDR removal and prior to FTAI. Across treatments and biological types, heifers that expressed estrus prior to AI achieved higher (P < 0.0001) AI pregnancy rates than heifers failing to express estrus. Pregnancy rates to FTAI did not differ significantly based on treatment in either biological type. Higher rates of estrous cyclicity among Bos taurus heifers resulted in higher FTAI pregnancy rates among Bos taurus (51%; 290/574) compared to Bos indicus-influenced heifers (39%; 218/565). However, pregnancy rates of respective RTS did not differ based on biological type. In summary, long-term CIDR-based protocols provide a simple, effective method of estrus synchronization in Bos indicus-influenced and Bos taurus beef heifers. Moreover, these results highlight the importance of management practices that result in high rates of estrous cyclicity prior to protocol initiation, particularly among later maturing breeds and biological types.

Split-time artificial insemination in beef cattle: II. Comparing pregnancy rates among nonestrous heifers based on administration of GnRH at AI.

This experiment was designed to evaluate split-time artificial insemination (AI) in beef heifers following administration of the 14-day controlled internal drug release (CIDR)-prostaglandin F2α (PG) protocol and to compare pregnancy rates among nonestrous heifers based on administration of GnRH at AI. Estrus was synchronized for 1138 heifers across six locations. Heifers received a CIDR insert (1.38 g progesterone) on Day 0 with removal on Day 14. Estrus detection aids (Estrotect) were applied at PG (25 mg), 16 days after CIDR removal on Day 30. Heifers were assigned to balanced treatments based on reproductive tract score and weight, and treatments were represented within each location. Split-time AI was performed at 66 and 90 hours after PG, and estrus was recorded at these times. Heifers in both treatments that exhibited estrus by 66 hours were inseminated and did not receive GnRH, whereas AI was delayed 24 hours until 90 hours after PG for heifers that failed to exhibit estrus by 66 hours. For heifers in treatment 1 that were inseminated at 90 hours, GnRH (100 µg) was administered concurrent with AI at 90 hours. Heifers in treatment 2 that were inseminated at 90 hours did not receive GnRH. Estrous response did not differ between treatments at 66 hours after PG (treatment 1 = 70%; treatment 2 = 71%; P = 0.58) or during the 24-hour delay period (treatment 1 = 59%; treatment 2 = 52%; P = 0.21). There was no effect of treatment on pregnancy rates resulting from AI for heifers inseminated at 66 hours (treatment 1 = 58%; treatment 2 = 62%; P = 0.86) or 90 hours (treatment 1 = 44%; treatment 2 = 39%; P = 0.47) after PG; and there was no difference between treatments when considering total AI pregnancy rate (treatment 1 = 54%; treatment 2 = 56%; P = 0.60). Ovulation was confirmed via ultrasonography for a subset of heifers that failed to exhibit estrus prior to 90 hours after PG. For heifers that failed to exhibit estrus by 90 hours, success of ovulation did not differ between treatments (treatment 1 = 52%; treatment 2 = 50%; P = 0.64) nor did AI pregnancy rate (treatment 1 = 24%; treatment 2 = 15%; P = 0.97). In summary, when split-time AI was used in conjunction with the 14-day CIDR-PG protocol in heifers, comparable pregnancy rates were achieved without administering GnRH.

Comparing strategies to synchronize estrus before fixed-time artificial insemination in primiparous 2-year-old beef cows.

Two experiments evaluated controlled internal drug release (CIDR)-based protocols to synchronize estrus in primiparous 2-year-old beef cows. In each experiment, treatments were balanced according to body condition score and days postpartum. Experiment 1 compared the 14-day CIDR-PG (14-d) and 7-day CO-Synch + CIDR (7-d) protocols on the basis of estrous response, pregnancy rates after fixed-time artificial insemination (FTAI), and final pregnancy rate. Cows assigned to 14-d (n = 355) received a CIDR insert on Day 0 with removal on Day 14. Cows assigned to 7-d (n = 349) received gonadotropin releasing hormone (GnRH) and a CIDR insert on Day 23. On Day 30, CIDRs were removed from 7-d cows, and PGF2α was administered to all cows in each treatment. On Day 33, GnRH was administered concurrent with FTAI at 66 and 72 hours after PGF2α for 7-d and 14-d treated cows, respectively. Estrous response before FTAI was higher for 7-d compared with 14-d cows (74% vs. 43%, respectively; P < 0.0001); however, pregnancy rates resulting from FTAI were similar (14-d 63%; 7-d 64%; P = 0.52). Ovarian follicular dynamics and serum estradiol-17ß concentrations were evaluated among a subset of cows assigned to each protocol. Dominant follicle diameter was smaller at PGF2α (P = 0.04) and FTAI (P = 0.002) among 14-d cows compared with 7-d cows; however, estradiol-17ß at PGF2α (P = 0.06) and FTAI (P = 0.001) was greater for 14-d versus 7-d treated cows. Experiment 2 compared estrous response and pregnancy rates in 2-year-old beef cows after FTAI- or split-time artificial insemination (STAI) following synchronization of estrus with the 14-day protocol. Cows assigned to FTAI (n = 266) were inseminated at a fixed time concurrent with GnRH at 72 hours after PGF2α regardless of estrus expression, whereas cows assigned to STAI (n = 257) were inseminated based on estrus expression as determined by activation of an estrus detection aid. Cows assigned to STAI that exhibited estrus by 72 hours were inseminated; however, AI was delayed until 24 hours after GnRH (96 hours after PGF2α) for nonestrous cows. Total estrous response was increased for STAI- versus FTAI-treated cows (STAI 64%; FTAI 42%; P < 0.0001); pregnancy rates resulting from AI were similar (STAI 55%; FTAI 56%; P = 0.60). In summary, the 14-day CIDR-PG and 7-day CO-Synch + CIDR protocols can be used effectively to synchronize estrus before FTAI in primiparous 2-year-old beef cows. Although expression of estrus was increased using STAI in conjunction with the 14-day protocol, this approach did not increase pregnancy rates compared with FTAI.

Split-time artificial insemination in beef cattle: I-Using estrous response to determine the optimal time(s) at which to administer GnRH in beef heifers and postpartum cows.

Two experiments evaluated timing of GnRH administration in beef heifers and cows on the basis of estrous status during split-time artificial insemination (AI) after controlled internal drug release (CIDR) based protocols. In experiment 1, estrus was synchronized for 816 pubertal and prepubertal or peripubertal heifers using the 14-day CIDR-PGF2α (PG) protocol, and in experiment 2, estrus was synchronized for 622 lactating cows using the 7-day CO-Synch + CIDR protocol. For both experiments, estrus detection aids (Estrotect) were applied at PG, with estrus recorded at 66 and 90 hours after PG. Treatments were balanced across locations for heifers using reproductive tract score and weight; whereas for cows, treatments were assigned and balanced to treatment according to age, body condition score, and days postpartum. Timing of AI for heifers and cows was on the basis of estrus expression 66 hours after PG. Females in each treatment that exhibited estrus before 66 hours were inseminated at 66 hours, whereas AI was delayed 24 hours until 90 hours after PG for females failing to exhibit estrus before 66 hours. Females in treatment one received GnRH 66 hours after PG irrespective of estrus expression; however, in treatment 2, GnRH was administered coincident with delayed AI only to females not detected in estrus at 66 hours after PG. Among heifers, there was no effect of treatment on overall estrous response (P = 0.49) or AI pregnancy rate (P = 0.54). Pregnancy rate for heifers inseminated at 66 hours was not influenced by GnRH (P = 0.65), and there were no differences between treatments in estrous response during the 24 hours delay period (P = 0.22). Cows in treatment 2 had a greater (P = 0.04) estrous response during the 24-hour delay period resulting in a greater overall estrous response (P = 0.04), but this did not affect AI pregnancy rate at 90 hours (P = 0.51) or total AI pregnancy rate (P = 0.89). Pregnancy rate resulting from AI for cows inseminated at 66 hours was not influenced by GnRH (P = 0.50). In summary, when split-time AI was used with the 14-day CIDR-PG protocol in heifers or the 7-day CO-Synch + CIDR protocol in cows, administration of GnRH at AI to females that exhibited estrus before 66 hours after PG was not necessary. Furthermore, among heifers for which AI was delayed on the basis of failure to exhibit estrus before 66 hours after PG, timing of GnRH (66 vs. 90 hours after PG) was more flexible. Delayed administration of GnRH to 90 hours after PG coincident with AI for cows that failed to exhibit estrus before 66 hours improved overall estrous response; however, in this study, a corresponding increase in pregnancy rate resulting from AI was not observed.

Effects of administration of prostaglandin F at initiation of the seven-day CO-Synch+controlled internal drug release ovulation synchronization protocol for suckled beef cows and replacement beef heifers.

Two experiments were conducted to determine the effect of administering PGF at the initiation of the 7-d CO-Synch+controlled internal drug release (CIDR) fixed-timed AI (TAI) protocol on pregnancy rates of suckled beef cows and replacement heifers. Within location, cows were stratified by days postpartum (DPP), BCS, and parity (Exp. 1; = 1,551) and heifers were stratified by BCS (Exp. 2; = 999) and randomly assigned to 1 of 2 treatments: 1) CO-Synch+CIDR (100-µg injection of GnRH at CIDR insertion [d -10] with a 25-mg injection of PGF at CIDR removal [d -3] followed by injection of GnRH and TAI on d 0) or 2) PG-CO-Synch+CIDR (a 25-mg injection of PGF on d -10 of the CO-Synch+CIDR protocol). Follicle diameter and corpus luteum (CL) development were assessed on d -10 and -3, and pregnancy status was determined on d 30 to 35. Blood was collected on d -20, -10, -3, and 0 relative to TAI to determine concentrations of progesterone (P4). In Exp. 1, TAI pregnancy rates did not differ ( = 0.667) between treatments and were affected by BCS ( = 0.003) and DPP ( = 0.006). Concentrations of P4 were greater ( < 0.0001) on d -3 for CO-Synch+CIDR than for PG-CO-Synch+CIDR (4.1 ± 0.2 and 3.4 ± 0.2 ng/mL, respectively). Follicle diameter on d -3 differed ( = 0.05) between PG-CO-Synch+CIDR (13.4 ± 0.3 mm) and CO-Synch+CIDR (12.5 ± 0.3 mm) treatments. Cows with P4 > 2.5 ng/mL on d -10 had greater ( = 0.024) pregnancy rate to TAI (56.5%) compared with cows with 2.5 ng/mL < P4 > 1 (43.0%), whereas cows with P4 < 1 ng/mL were intermediate (51.6%). Cows with a CL on d -10 had greater ( = 0.012) pregnancy rates to TAI than cows without a CL (66.3 vs. 39.4%, respectively). In Exp. 2, TAI pregnancy rates did not differ ( = 0.316) between treatments. Concentrations of P4 differed ( < 0.0001) on d -3 with greater concentrations of P4 for CO-Synch+CIDR than for PG-CO-Synch+CIDR (3.75 ± 0.20 ng/mL and 3.60 ± 0.21 ng/mL, respectively). Follicle diameter was similar ( = 0.749) between treatments on d -10 and -3. Regardless of treatment, cyclic status tended ( = 0.062) to improve pregnancy rates to TAI (55 vs. 45%, for cycling and noncycling heifers, respectively). We concluded that addition of PGF to the 7-d CO-Synch+CIDR protocol decreased concentrations of P4 in cows and heifers and increased follicle diameter at CIDR removal in cows but failed to increase TAI pregnancy rates.

Delayed insemination of non-estrous heifers and cows when using conventional semen in timed artificial insemination.

Two experiments were designed to test the hypothesis that pregnancy rates after fixed-time artificial insemination (FTAI) in beef heifers and cows may be improved by delaying insemination of females that have not expressed estrus before FTAI. In Exp. 1, estrus was synchronized for 931 heifers across 3 locations using the 14-d CIDR-PG protocol (controlled internal drug-release [CIDR] insert [1.38 gm progesterone] on d 0 with removal of CIDR insert on d 14; 25 mg PGF2α 16 d after CIDR insert removal on d 30; and 100 µg GnRH on d 33, 66 h after PGF2α). Estrous detection aids (Estrotect) were applied at PGF2α on d 30, and estrous expression was recorded at GnRH on d 33. Heifers within each location were randomly assigned to 1 of 2 treatments based on weight and reproductive tract score (RTS): 1) FTAI (concurrent with GnRH, 66 h after PGF2α) regardless of estrous expression or 2) FTAI for heifers expressing estrus and delayed AI (20 h after GnRH) for heifers failing to express estrus. Heifers assigned to treatment 2 achieved a higher AI pregnancy rate than heifers assigned to treatment 1 (54 versus 46%; P = 0.01). The observed increase in AI pregnancy rate is attributed to the delayed AI of non-estrous heifers in treatment 2, as AI pregnancy rates for non-estrous heifers were significantly higher for treatment 2 (49 versus 34%; P = 0.02), while AI pregnancy rates of estrous heifers did not differ by treatment (P = 0.24). In Exp. 2, estrus was synchronized for 951 mature, suckled cows across 9 locations using the 7-d CO-Synch + CIDR protocol (100 µg GnRH + CIDR insert [1.38 gm progesterone] on d 0; 25 mg PGF2α at CIDR insert removal on d 7; and 100 µg GnRH on d 10, 66 h after CIDR insert removal). Estrus detection aids (Estrotect) were applied at PGF2α and CIDR insert removal on d 7, and estrous expression was recorded at GnRH on d 10. Cows within each location were assigned to 1 of 2 treatments based on age, days postpartum, and BCS: 1) FTAI (concurrent with GnRH, 66 h after PGF2α) regardless of estrous expression or 2) FTAI for cows expressing estrus and delayed AI (20 h after GnRH) for cows failing to express estrus. No significant effect of treatment was found on AI pregnancy rate (P = 0.76). In summary, FTAI pregnancy rates in heifers can be improved through a strategy of "split-time" AI. However, a statistically significant increase was not observed in the pregnancy rates of mature suckled cows when using a similar strategy.

Comparison of a 16- versus a 19-day interval between controlled internal drug release removal and prostaglandin F2α following a 14-day controlled internal drug release treatment and fixed-time artificial insemination in postpartum beef cows.

This experiment compared 2 long-term controlled internal drug release (CIDR)-based protocols to synchronize estrus before fixed-time artificial insemination (FTAI) in postpartum beef cows. Cows were assigned to treatments by age, BCS, and days postpartum. Cows assigned to the 14- to 19-d CIDR-PGF2α protocol (n = 196) received CIDR inserts (1.38 g progesterone [P4]) from d 0 to 14 and PGF2α (25 mg, i.m.) 19 d after CIDR removal on d 33. Cows assigned to the 14-to-16-d CIDR-PGF2α protocol (n = 195) received CIDR inserts from d 3 to 17 and PGF2α 16 d after CIDR removal on d 33. Cows were artificially inseminated on d 36, 72 h after PGF2α, with GnRH (100 µg, i.m.) at FTAI. Cows were exposed for natural service 14 d after FTAI for 75 d. Blood samples for P4 were collected at d -10 and 0 to determine pretreatment estrous cyclicity status and again at PGF2α. Blood samples for estradiol (E2) were collected at PGF2α and FTAI. HeatWatch estrus detection transmitters were used from CIDR removal until FTAI to determine onset of estrus after CIDR removal and PGF2α. Dominant follicle diameter was determined at PGF2α and FTAI. Pregnancy diagnosis was performed 70 d after FTAI and confirmed at d 140 of gestation. Estrous response after CIDR removal was similar between treatments. Cows in both treatments had similar size dominant follicles on d 33 at PGF2α and d 36 at FTAI. Progesterone at PGF2α was greater (P = 0.03) for 14-to-16-d compared to 14-to-19-d treated cows. Mean concentrations of E2 at PGF2α were similar between treatments but were greater (P = 0.01) at FTAI for 14-to-16-d compared to 14-to-19-d treated cows. Estrous response after PGF2α was greater (P < 0.01) for 14-to-19-d compared to 14-to-16-d treated cows (47.4 vs. 29.7%, respectively). Pregnancy rate resulting from FTAI was affected by the treatment × age group interaction (P = 0.08). Pregnancy rate after FTAI among cows ≥ 4 yr tended to be greater (P = 0.06) for 14-to-19-d compared to the 14-to-16-d treated cows, suggesting that the 14-to-19-d schedule works better for older age cows compared with the 14-to-16-d schedule. Final pregnancy rates were similar between the 2 treatments. In summary, these data indicate that a range in intervals from CIDR removal to PGF2α may be feasible when using long-term CIDR-based protocols in cows and raise questions that warrant further study regarding the benefits of extending this interval based on cow age.

Delayed insemination of nonestrous cows improves pregnancy rates when using sex-sorted semen in timed artificial insemination of suckled beef cows.

This experiment was designed to test the hypothesis that delayed insemination of nonestrous cows would increase pregnancy rates when using sex-sorted semen in conjunction with fixed-time artificial insemination (FTAI). Estrus was synchronized for 656 suckled beef cows with the 7-d CO-Synch + controlled internal drug release (CIDR) protocol (100 µg GnRH + CIDR [1.38 g progesterone] on d 0, 25 mg PGF2α at CIDR removal on d 7, and 100 µg GnRH on d 10, 66 h after CIDR removal). Estrus detection aids (Estrotect) were applied at PGF2α and CIDR removal on d 7, and estrous expression was recorded at GnRH on d 10. Cows were assigned to 1 of 3 treatments: 1) FTAI (concurrent with GnRH, 66 h after CIDR removal) with conventional semen regardless of estrous expression, 2) FTAI with sex-sorted semen regardless of estrous expression, or 3) FTAI with sex-sorted semen for cows having expressed estrus and delayed AI 20 h after final GnRH for cows failing to express estrus. A treatment × estrous expression interaction was found (P < 0.0001). Higher pregnancy rates (P < 0.0001) were achieved with conventional semen (Treatment 1; 77%) than with sex-sorted semen (Treatments 2 and 3; 51 and 42%, respectively) among cows that expressed estrus. However, among cows that failed to express estrus, delayed insemination with sex-sorted semen yielded higher (P < 0.0001) pregnancy rates than with sex-sorted semen at the standard time (Treatments 2 and 3; 3 versus 36%, respectively). Furthermore, among cows that failed to express estrus, FTAI pregnancy rates when using sex-sorted semen at the delayed time (36%) were comparable (P = 0.9) to those achieved using conventional semen at the standard time (Treatment 1; 37%). These results indicate that delaying AI of nonestrous cows by 20 h from the standard FTAI improves pregnancy rates when sex-sorted semen is used with FTAI.

Comparison of long-term controlled internal drug release-based protocols to synchronize estrus and ovulation in postpartum beef cows.

Two experiments were conducted to examine the necessity of adding a GnRH injection to a 14-d controlled internal drug release (CIDR)-based protocol for synchronization of estrus and ovulation in postpartum beef cows. The experiments were designed to characterize long-term CIDR-based protocols in cyclic and noncyclic postpartum beef cows on the basis of estrous response, follicular dynamics, and serum steroid hormone concentrations. In Exp. 1 and 2, crossbred lactating beef cows (n = 40 and 38, respectively) were randomly assigned to 1 of 2 treatments by age, days postpartum (DPP), BCS, and estrous cyclicity status: 1) cows received a CIDR from d 0 to 14 followed by GnRH 9 d after CIDR removal (d 23) and PGF2α on d 30 (CIDR Select) or 2) CIDR administration from d 0 to 14 followed by PGF2α 16 d later (d 30; Show-Me-Synch). Estrus detection was performed using HeatWatch transmitters applied from CIDR removal to AI. Cows in Exp. 1 were artificially inseminated based on detected estrus whereas cows in Exp. 2 were inseminated at a fixed time. In both experiments, follicle turnover on d 25 of treatment was greater among CIDR Select-treated cows (P < 0.001) compared with Show-Me-Synch-treated cows. In Exp. 1, CIDR Select-treated cows tended to have a reduced (P = 0.06) variance for the interval to estrus after PGF2α than Show-Me-Synch-treated cows. Also, cows assigned to the CIDR Select protocol had greater concentrations of progesterone (P < 0.05) on the day before PGF2α administration as well as greater concentrations of estradiol-17ß (P < 0.01) 48 h after PGF2α administration. In Exp. 2, mean dominant follicle diameter on d 23 and at fixed-time AI (FTAI) did not differ between treatments (P > 0.10), but Show-Me-Synch-treated cows had larger follicles at d 28 (P < 0.001) and tended to have larger follicles at PGF2α (d 30; P = 0.06) compared with cows assigned to CIDR Select. In summary, the administration of GnRH on d 23 of a long-term CIDR-based estrus synchronization protocol increased follicle turnover; however, both long-term CIDR-based protocols yielded similar physiological outcomes among estrous-cycling and anestrous postpartum beef cows.

Hot topic: Comparison of sex-sorted and conventional semen within a fixed-time artificial insemination protocol designed for dairy heifers.

The objective was to compare pregnancy per AI (P/AI) with conventional (CON) or sex-sorted (SS) semen from a single sire within a fixed-time AI (FTAI) program designed for dairy heifers. Holstein heifers (n=240) were assigned to treatment (CON or SS) according to body weight and reproductive tract score. All heifers underwent FTAI by using the "Show-Me-Synch" protocol [controlled internal drug release (CIDR) insert from d 0 to 14 followed by PGF(2α) (25mg i.m.) 16d after insert removal (d 30) with GnRH (100 µg i.m.) and FTAI at 66 h after PGF(2α)]. A single professional technician performed the FTAI. Heifers were fitted with heat detection patches at PGF(2α) to characterize estrous response. Estrous response did not differ between CON (63/120; 53%) and SS (70/120; 58%) treatments. The CON heifers, however, achieved greater FTAI P/AI (82/120; 68%) compared with SS (45/120; 38%) heifers. The P/AI did not differ for CON heifers that exhibited or failed to exhibit estrus before FTAI [44/63 (70%) vs. 38/57(67%), respectively]. For SS heifers, however, those that exhibited estrus had greater P/AI compared with those that failed to exhibit estrus [32/70 (46%) vs. 13/50 (26%)]. Pregnancy per AI resulting from FTAI was greater for heifers that were inseminated with CON semen compared with those that received SS semen. The expression of estrus before FTAI did not affect P/AI when CON semen was used, whereas the P/AI with SS semen was greater for heifers detected in estrus. Further studies are required to develop strategies for using sex-sorted semen when inseminating heifers at predetermined fixed times on the basis of expression of estrus before FTAI.

EXTENSION EDUCATION SYMPOSIUM: reinventing extension as a resource--what does the future hold?

The mission of the Cooperative Extension Service, as a component of the land-grant university system, is to disseminate new knowledge and to foster its application and use. Opportunities and challenges facing animal agriculture in the United States have changed dramatically over the past few decades and require the use of new approaches and emerging technologies that are available to extension professionals. Increased federal competitive grant funding for extension, the creation of eXtension, the development of smartphone and related electronic technologies, and the rapidly increasing popularity of social media created new opportunities for extension educators to disseminate knowledge to a variety of audiences and engage these audiences in electronic discussions. Competitive grant funding opportunities for extension efforts to advance animal agriculture became available from the USDA National Institute of Food and Agriculture (NIFA) and have increased dramatically in recent years. The majority of NIFA funding opportunities require extension efforts to be integrated with research, and NIFA encourages the use of eXtension and other cutting-edge approaches to extend research to traditional clientele and nontraditional audiences. A case study is presented to illustrate how research and extension were integrated to improve the adoption of AI by beef producers. Those in agriculture are increasingly resorting to the use of social media venues such as Facebook, YouTube, LinkedIn, and Twitter to access information required to support their enterprises. Use of these various approaches by extension educators requires appreciation of the technology and an understanding of how the target audiences access information available on social media. Technology to deliver information is changing rapidly, and Cooperative Extension Service professionals will need to continuously evaluate digital technology and social media tools to appropriately integrate them into learning and educational opportunities.

Comparison of long- versus short-term CIDR-based protocols to synchronize estrus prior to fixed-time AI in postpartum beef cows.

This experiment was conducted to compare pregnancy rates in postpartum beef cows resulting from fixed-time AI (FTAI) after treatment with controlled internal drug release (CIDR)-based protocols to synchronize estrus. Cows assigned to the Show-Me-Synch (n=167) protocol received a CIDR from d 0 to 14, and prostaglandin F(2α) (PGF(2α)) on d 30. Cows assigned to 7-d CO-Synch+CIDR (n=177) received a CIDR and gonadotropin releasing hormone (GnRH) on d 23. On d 30, CIDRs were removed and PGF(2α) was administered. Blood sampling occurred on d -10 and 0 of treatment to determine estrous cyclicity status (progesterone ≥0.5 ng/mL estrous cycling). Treatments were balanced on age, DPP and BCS. Estrous detection was performed using HeatWatch from PGF(2α) to FTAI. Artificial insemination was performed at predetermined fixed times (72 h, Show-Me-Synch; 66h, 7-d CO-Synch+CIDR) and all cows were administered GnRH at FTAI. This experiment was conducted over a two year period; no differences were found between years so the data were pooled for further analysis. Pregnancy rate resulting from FTAI did not differ (P>0.10) between technicians or AI sires. Pregnancy rate resulting from FTAI was similar between treatments (P=0.20); however, cows that exhibited estrus prior to FTAI had a higher pregnancy rate (P<0.01) than for those that did not. Pregnancy rate at the end of the breeding period was similar between treatments (P=0.28). In summary, FTAI pregnancy rates were similar among postpartum beef cows following treatment with either a short- or long-term CIDR-based estrous synchronization protocol.