Hormonal combinations aiming to improve reproductive outcomes of Bos indicus cows submitted to estradiol/progesterone-based timed AI protocols.

The aim was to study reproductive outcomes of Nelore (Bos indicus) cows submitted to a 7-d estradiol (E2)/progesterone (P4)-based timed artificial insemination (TAI) protocol, receiving various combinations of doses and hormones. Primiparous (n = 962) and multiparous (n = 1935) cows were submitted to synchronization (n = 2012) and resynchronization (n = 885 non-pregnant cows at pregnancy diagnosis 30 d after TAI) protocols, following a 2 × 2 × 2 factorial arrangement of eight treatments. At the initiation of the TAI protocol (Day -9), all cows received a 1.0 g intravaginal P4 insert, 2.0 mg E2 benzoate and received (PGF1) or not (PGF0) 0.5 mg cloprostenol sodium (PGF). On Day -2, the P4 insert was removed, all cows received 0.5 mg PGF, 300 IU equine chorionic gonadotropin (eCG) and 0.5 (EC0.5) or 1.0 mg estradiol cypionate (EC1.0). On Day 0, cows were treated (G1) with 8.4 µg buserelin acetate (GnRH) or not (G0), concurrently with TAI. The eight treatments were generated: 1) PGF0-EC0.5-G0 (n = 364), 2) PGF0-EC0.5-G1 (n = 363), 3) PGF1-EC0.5-G0 (n = 363), 4) PGF1-EC0.5-G1 (n = 360), 5) PGF0-EC-1.0-G0 (n = 360), 6) PGF0-EC1.0-G1 (n = 363), 7) PGF1-EC1.0-G0 (n = 361), and 8) PGF1-EC1.0-G1 (n = 363). Pregnancy per AI (P/AI) was greater at first AI compared with resynchronization (58.9 [n = 2012] vs. 54.9% [n = 885]). Presence of CL on Day -9 resulted in more cows expressing estrus (81.3 [n = 680] vs. 67.1% [n = 2033]) and greater P/AI (66.0 [n = 692] vs. 54.9% [n = 2106]). There was no difference in P/AI between cows that received or not PGF on Day -9 (58.7 [n = 1447] vs. 56.6% [n = 1450]). In contrast, PGF tended to increase P/AI of cows with CL on Day -9 (with PGF = 69.1 [n = 375] vs. without PGF = 62.5% [n = 317]). Cows that received 1.0 mg EC expressed more estrus than those treated with 0.5 mg (73.8 [n = 1414] vs. 67.9% [n = 1398]) and had greater P/AI (60.2 [n = 1447] vs. 55.1% [n = 1450]). P/AI was greater in cows treated with GnRH at TAI (59.8 [n = 1449] vs. 55.5% [n = 1448]), particularly in cows that did not show estrus (52.7 [n = 393] vs. 38.1% [n = 420]). Moreover, GnRH on Day 0 increased P/AI in cows with BCS < 3.0 (57.1 [n = 723] vs. 48.6% [n = 698]), in primiparous (50.1 [n = 465] vs. 41.9% [n = 497]) and in cows that received 0.5 mg EC (58.9 [n = 723] vs. 51.3% [n = 727]). In conclusion, 1.0 mg of EC on Day -2 and GnRH at TAI improved P/AI, but the combination of a higher dose of EC and GnRH treatment at AI did not enhance this effect. Furthermore, GnRH improved P/AI especially in Bos indicus cows with lower expression of estrus, such as primiparous, thinner cows, and cows treated with 0.5 mg of EC.

Progesterone-based timed AI protocols for Bos indicus cattle II: Reproductive outcomes of either EB or GnRH-type protocol, using or not GnRH at AI.

The aim of these experiments was to study ovarian dynamics and fertility of Bos indicus beef cattle submitted to 7-d progesterone (P4)-based fixed-time AI (FTAI) protocols using different hormonal treatments. In Exp. 1, 2 yr old Nelore heifers (n = 973) were randomly assigned to one of four treatments: EB-0 (estradiol benzoate, EB on D0 and no GnRH at AI), EB-G (EB on D0 and GnRH at AI), G-0 (GnRH on D0 and no GnRH at AI), or G-G (GnRH on D0 and at AI). On D0, heifers received an intravaginal P4 implant (0.5 g) for 7 d and EB (1.5 mg) or GnRH (16.8 µg). On D7, the P4 implant was withdrawn and heifers received cloprostenol (PGF; 0.5 mg) and estradiol cypionate (EC, 0.5 mg). Heifers in G groups also received PGF and eCG (200 IU) on D6, whereas EB heifers received eCG on D7. At FTAI on D9, only EB-G and G-G groups received GnRH (8.4 µg). In Exp. 2, Nelore cows (n = 804) received the same treatments (EB-0, EB-G, G-0, or G-G) using a 1.0 g P4 implant, 2.0 mg EB, and 300 IU eCG. Effects were considered significant when P ≤ 0.05. After treatment on D0, G had more ovulations than EB in heifers (60.3 [287/476] vs. 12.7% [63/497]) and cows (73.7 [83/112] vs. 24.4% [28/113]). Luteolysis after D0 was greater in EB than G in heifers (39.2 [159/406] vs. 20.0% [77/385]) and cows (25.5 [14/55] vs. 1.6% [1/64]). Heifers in G had larger follicles (mm) than EB on D7 (10.3 ± 0.2 vs. 9.2 ± 0.2) and at AI (11.9 ± 0.2 vs. 11.3 ± 0.2). Cows had larger follicles in G than EB on D7 (11.0 ± 0.3 vs. 9.9 ± 0.3) but not at AI. More estrus was observed in G than EB for heifers (80.3 [382/476] vs. 69.6% [346/497]) and cows (67.6 [270/400] vs. 56.2% [227/404]). There was no interaction between D0 and D9 treatments on pregnancy per AI (P/AI) in heifers (EB-0: 56.7 [139/245], EB-G: 53.6 [135/252], G-0: 52.6 [127/241], and G-G: 57.5% [135/235]). However, cows from EB-G had greater P/AI than EB-0 (69.5 [142/204] vs. 60.2% [120/200]), whereas P/AI for G-0 (62.7% [127/203]) was similar to G-G (60.9% [120/197]). In heifers, there was no interaction of GnRH at AI with estrus, however, cows that did not display estrus had greater P/AI if they received GnRH at AI (GnRH = 59.1 [91/154] vs. No GnRH = 48.2% [78/162]). Thus, protocols initiated with EB or GnRH for Bos indicus heifers and cows had differing ovarian dynamics but similar overall fertility, enabling their use in reproductive management programs. Treatment with GnRH at time of AI increased fertility in some instances in Bos indicus cows but not in heifers.

Luteolysis in Bos indicus cows on Days 5 and 7 of estrous cycle with varying doses of PGF2α.

The aim of this study was to evaluate luteolysis using three doses of PGF2α on Day 5 or Day 7 of the estrous cycle in nonlactating Nellore (Bos indicus) cows. Cows (n = 323) were assigned within date of estrus (Day 0 of estrous cycle) to receive 12.5, 25.0, or 50.0 mg of PGF2α on either Day 5 or Day 7 of the estrous cycle in a 3 × 2 factorial arrangement. Blood samples for progesterone (P4) concentrations were collected at 0, 24, 48, and 72 hours after PGF2α to assess luteolysis (L). Luteolysis was defined on the basis of P4 concentrations at 72 hours using either less than 0.5 ng/mL (L0.5) or less than 1.0 ng/mL (L1.0) as the cut off. Luteolysis was considered "partial" when P4 concentration declined within 24 hours after PGF2α but failed to decline further or, in some cases, increased. Incidence of luteolysis was less (P < 0.01) on Day 5 than Day 7 of the estrous cycle (17.3 vs. 47.6% and 30.4 vs. 77.2%; for L0.5 and L1.0, respectively). Dose of PGF2α increased (P < 0.01) L1.0 (12.5 mg = 38.9%; 25.0 mg = 52.3%; and 50.0 mg = 70.4%). Incidence of partial luteolysis for cows on Day 5 (57.1%) was greater (P < 0.01) than that on Day 7 (19.1%) of the estrous cycle and was more prevalent (P < 0.01) with lower doses of PGF2α (12.5 mg = 49.1%; 25.0 mg = 37.4%; and 50.0 mg = 27.8%). In conclusion, both days of the estrous cycle and doses of PGF2α influenced the incidence of complete and partial luteolysis in Nellore cows and should be an important consideration when devising estrus synchronization programs in this species.

Avaliação da reutilização de implantes contendo progestágenos na taxa de prenhez em vacas de corte / Evaluation of used progestagen implants on pregnancy rate in beef cows

Duzentos e vinte e uma vacas (78 paridas com bezerros entre 40 e 90 dias de idade e as demais secas vazias) Nelore (Bos taurus indicus) e mestiças Charolês (Bos taurus taurus) foram utilizadas para avaliar a reutilização de implantes auriculares de silicone impregnados com progestágenos para controle farmacológico do ciclo estral e ovulação sobre a taxa de prenhez. Os tratamentos experimentais consistiram de três protocolos para sincronização do cio e inseminação artificial em tempo fixo (IATF). No tratamento 1 (T1; n=73) as vacas receberam um implante auricular de Crestar® (3 mg de norgestomet); no tratamento 2 (T2; n= 75) as vacas receberam um implante auricular de Crestar® já utilizado previamente; e no tratamento 3 (T3; n=73) as vacas receberam dois implantes auriculares de Crestar® também utilizados previamente. Além dos implantes, as vacas receberam aplicação intramuscular (i.m) 2 mL de progesterona (25 mg/mL) + 2 mL de benzoato de estradiol i.m (1 mg/mL) no momento da colocação dos implantes. Os implantes foram removidos após 8 dias junto a uma aplicação de 2,0 mL de Preloban® i.m (150 g de D-cloprostenol). Após 24 h da remoção do implante, aplicou-se 1 mL de Estrogin® i.m (1 mg de benzoato de estradiol). A IATF foi realizada 54-56 h após a retirada dos implantes. Não houve diferença na taxa de prenhez das vacas, sendo 39,72%, 34,21% e 36,98% para os tratamentos T1, T2 e T3, respectivamente. A reutilização de implantes com progestágeno (Crestar®) não alterou a taxa de prenhez de vacas aptas à reprodução.

Two-hundred and twenty-one (78 suckling - 40 to 90 days and 143 not suckling ) Nelore (Bos taurus indicus) and crossbred Charolais (Bos taurus taurus) cows were used to evaluate the reutilization of progestagen implants to pharmacological control of the estrus cycle and ovulation on pregnancy rate. Cows were randomly assigned to one of three protocols for estrous synchronization and pre-fixed time artificial insemination (FTAI) was performed. In treatment 1 (T1; n=73) cows were implanted with Crestar® (3 mg de norgestomet); in treatment 2 (T2; n= 75) cows were implanted with already used Crestar®, and in treatment 3 (T3; n=73) cows received two Crestar® implants, also both previously used. All cows were injected with 2 mL of progesterone (25mg/mL) + 1 mL estradiol benzoate (1 mg/mL i.m.) at the time of implants insertion, intramuscular (i.m). Implants were removed after 8 days and 2 mL of Preloban® (150 g de D-cloprostenol) were administered i.m. Twenty-four hours after implants removal, cows were injected with 1 mL (i.m.) of Estrogin® (1mg of estradiol benzoate). The FTAI was performed 54-56 h after implants removal. There was no difference (P>0.05) on cow’s pregnancy rate among treatments. Pregnancy rates were 39.72, 34.21 and 36.98% for T1, T2 and T3, respectively. Progestagen implants reutilization (Crestar®) did not affected pregnancy rate in beef cows ready for reproduction.

Uso do protocolo Crestar® em tratamentos utilizando benzoato de estradiol, PGF2alfa, PMSG e GnRH para controle do ciclo estral e ovulação em vacas de corte / Sincronization of ovulation utilizing the crestar® protocol associated with estradiol benzoate, PGF2alfa, PMSG and GnRH in beef cows

O objetivo foi avaliar a eficiência do controle da ovulação utilizando os hormônios PMSG, GnRH, Benzoato de Estradiol e PGF2 α junto ao protocolo Crestar®, para IA em tempo fixo. Foram utilizadas 348 vacas, cruzadas Nelore (Bos taurus indicus) X Charolês (Bos taurus taurus), divididas em dois grupos: 179 vacas paridas com 90 a 120 dias pós-parto e 169 vacas solteiras. Estes animais foram submetidos a cinco tratamentos: todas as vacas receberam o protocolo Crestar® como agente sincronizador do crescimento folicular. (implante subcutâneo com 3mg de norgestomet e injeção 3mg de norgestomet + 5mg de valerato de estradiol - i.m.). Após a remoção do implante (10 dias), as vacas foram submetidas aos cinco tratamentos de controle da ovulação: T1 - (n=70): injeção de solução fisiológica 48h após a retirada do implante (D 12); T2 - (n=68): 0,75mg de benzoato de estradiol 24h após a retirada do implante (D 11); T3 - (n=70): aplicação de 150µg de PGF2 α, no dia da retirada (D 10) e 0,75mg de benzoato de estradiol 24h após a retirada do implante (D 11); T4 - (n=70): 500 UI de PMSG na retirada do implante (D 10) e T5 - (n=70): 500µg de GnRH 48h após a retirada dos implante (D 12). Todos os animais foram inseminados 54-56h após a retirada do implante. As taxas de prenhez foram analisadas estatisticamente por regressão logística. Não houve diferença entre os tratamentos (p>0,05) onde: 35,7, 31,4, 22,0, 37,0 e 42,8% para T1, T2, T3, T4 e T5 respectivamente.

The objective of this study was to evaluate the effects of ovulationusing PMSG, GnRH, Estradiol Benzoate and PGF2α in combination with Crestar® protocol and AI at fixed time. Three hundred forty eight multiparous cows, crossbreed Nelore (Bos taurus indicus) X Charolais (Bos taurus taurus) were divided in two groups: 179 suckling cows and 169 non-suckling cows. Those cows received a Crestar® protocol for follicular growth synchronization consisting of a subcutaneous implant with 3mg of norgestomet and 3mg of norgestomet plus 5mg of estradiol valerate injection (day of implant insert). The implant was removed after nine days. Cows were submitted to five treatments for pharmacological control of ovulation and were artificially inseminated at fixed time: T1 - (n=70): injection of physiological solution 48h after implant removal (D 12); T2 - (n=68): 0.75mg of estradiol benzoate 24h after implant removal (D 11); T3 - (n=70): 150µg of PGF2α at same day of implant removal (D 9) and 0.75mg of estradiol benzoate 24h after implant removal (D 11); T4 - (n=70): the cows received 500 UI of PMSG at implant removal (D 10) and T5 - (n=70): cows received 500µg of GnRH 48h after implant removal (D 12). Those cows were artificially inseminated 54-56h after implant removal. Pregnancy rate was analyzed by logistical regression program. There were no differences among treatments (P>0.05) 35.7, 31.4, 22.0, 37.0 and 42.8% for T1, T2, T3, T4 and T5, respectively.