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This study evaluated the follicular dynamics and the pregnancy rates of Nelore cows with or without a CL synchronized with FTAI employing injectable progesterone (P4). Multiparous cows (n=44), 45-65 days postpartum were allocated into a 2x2 factorial. Eleven cows with and 11 without a CL received a conventional protocol of FTAI (D0/1 g P4 + 2 mg EB; D8/500 μg cloprostenol, 300 IU eCG and 24 h later 1 mg EB; D10/FTAI). Other 11 cows with and 11 without a CL received 350 mg of injectable P4 (300 mg sc and 50 mg im) and 2 mg of EB im on D0. On D6, 500 μg of cloprostenol and 300 IU of eCG were administered im. After 24 h, 1 mg of EB was administered im and FTAI was performed on D8. The results were analyzed by ANOVA and Tukey or by Chi-square test (p≤0.05). The presence of follicles ≥ 5mm on D4, follicular growth rate and CL diameter were similar between groups (50-55%, 1.1-1.2mm/ day and 16.1-17.6mm; respectively). The diameter of the dominant follicle (DF) at FTAI and ovulatory follicle (OF) were similar between groups with CL (10.5±1.8 and 11.4±1.3mm, respectively) and without CL (10.8±2.3 and 11.1±2.2mm, respectively) but device was higher than injectable (11.7±2.0 and 11.8±1.7 vs. 9.7±1.7 and 10.6±2.0mm, respectively). The ovulation and pregnancy rate were similar between groups with CL (59% and 36%, respectively) and without CL (77% and 27%, respectively) but device was higher than injectable (91% and 45% vs. 45.5% and 18%; respectively). The ciclicity did not affect the follicular dynamics and pregnancy rate. The device showed higher diameter of the DF at FTAI, OF and ovulation and pregnancy rates. However, the injectable P4 produced similar percentages of follicles ≥ 5 mm on D4, follicular growth rate and CL diameter, raising the possibility of further investigation. Key words: Bos indicus, ultrasonography, follicular growth, ovulation and dominant follicle ResumoEste estudo avaliou a dinâmica folicular e a taxa de prenhez de vacas Nelore, com ou sem CL sincronizadas com protocolo de IATF empregando progesterona injetável (P4). Vacas multíparas (n=44), 45-65 dias pós-parto foram alocados em um fatorial 2x2. Onze vacas com e 11 sem CL receberam um protocolo convencional de IATF (D0/1 g P4 + 2 mg BE; D8/500 μg cloprostenol, 300 UI eCG e 24 h depois 1 mg BE; D10/IATF). Outras 11 vacas com e 11 sem CL receberam 350 mg de P4 injetável (300 mg SC e 50 mg IM) e 2 mg de BE IM no D0. No D6, 500 μg de cloprostenol e 300 UI de eCG foram administradas IM. Morotti, F. ; Campos, J. T. ; Seneda, M. M.Após 24 h, 1 mg de BE foi administrado IM e IATF foi realizada no D8. Os resultados foram analisados por ANOVA e teste de Tukey ou Qui-quadrado (p≤0,05). A presença de folículos ≥ 5 mm no D4, a taxa de crescimento folicular e o diâmetro do CL foram semelhantes entre os grupos (50-55%, 1,1-1,2mm/ dia e 16,1-17,6mm, respectivamente). O diâmetro do folículo dominante (FD) na IATF e do folículo ovulatório (FO) foram semelhantes entre os grupos com CL (10,5±1,8 e 11,4±1,3 mm, respectivamente) e sem CL (10,8±2,3 e 11,1±2,2 m...

This study aims to evaluate ovarian follicular dynamics of Nelore cows subjected to fixed-time artificial insemination (FTAI) with injectable progesterone (P4) or intravaginal device. In the device group, 20 cows received an intravaginal device with 1 g P4 and administration of 2 mg estradiol benzoate (EB) intramuscularly (im) on D0. The device was removed on D8, followed by administration of 500 μg cloprostenol, 300 IU equine chorionic gonadotropin (eCG) and 1 mg estradiol cypionate (EC), im. The cows were inseminated 48h later. In the injectable group, 350 mg P4 (300 mg subcutaneously and 50 mg im) and 2 mg EB im were administered on D0 to 16 cows. On D6, 500 μg cloprostenol, 300 IU eCG and 1 mg EC were administered im. The FTAI was performed 48h later. Sixty-five percent of cows from the device group (13/20) and 75% from the injectable group (12/16) showed follicles ≥ 5 mm on D4 (p>0.05). The average rate of follicular growth was 0.92±0.25 mm/day for the device group and 1.06±0.45 mm/day for the injectable group (p>0.05). The average diameter of the dominant follicle (DF) at FTAI was 11.4±1.4 mm for the device group and 10.8±1.8 mm for the injectable group (p>0.05). In the device group, ovulatory follicles (OF) had an average diameter of 12.1±1.4 mm, and in the injectable group 12.3±1.6 mm (p>0.05). Ninety percent of the device group (18/20) and 37.5% of the injectable group (6/16) demonstrated ovulation (p<0.05). The average diameter of the corpus luteum (CL) was 18.7±4.3 mm for the device group and 17.7±3.6 mm for the injectable group. The injectable P4 showed similarity in the presence of follicles ≥ 5 mm on D4, follicular growth rate, diameters of the DF, OF and CL. However, the ovulation rate was higher in the device group. Key words: Bos indicus, ultrasonography, follicular growth, ovulation, dominant follicle ResumoO objetivo deste estudo foi avaliar a dinâmica folicular ovariana de vacas Nelore submetidas à inseminação artificial em tempo fixo (IATF) com progesterona injetável (P4) ou dispositivo intravaginal. No grupo dispositivo, 20 vacas receberam um dispositivo intravaginal com 1 g P4 e 2 mg benzoato de estradiol (BE) por via intramuscular (im) no D0. No D8 o dispositivo foi removido e 500 µg cloprostenol, 300 UI gonadotrofina coriônica equina (eCG) e 1 mg cipionato de estradiol (CE) foram aplicados, im. subcutânea e 50 mg, im) e 2 mg BE im no D0. No D6, 500 μg cloprostenol, 300 UI eCG e 1 mg CE foram administradas im. A IATF foi realizada 48h após o CE. No grupo dispositivo, 65% (13/20) e no grupo injetável 75% (12/16) das vacas apresentaram folículos ≥ 5 mm no D4 (p>0,05). A taxa média de crescimento folicular foi de 0,92±0,25 mm/dia para o grupo dispositivo e 1,06±0,45 mm/dia para o grupo injetável (p>0,05). O diâmetro médio do folículo dominante na IATF foi 11,4±1,4 mm para o grupo dispositivo e 10,8±1,8 mm para o injetável (p>0,05). O diâmetro médio do folículo ovulatório foi 12,1±1,4 mm no grupo dispositivo e 12,3±1,6 mm no grupo injetável (p>0,05). A ovulação ocorreu em 90% (18/20) ...

Most fixed-time artificial insemination (FTAI) protocols utilize progesterone (P4) as a hormonal source to achieve synchronization of estrus in cattle. The use of an injectable P4 source to control estrus would be an interesting pharmacological strategy owing to the practicality of parenteral application. However, the effects of injectable P4 on estrus cycle control in cattle remain poorly studied. In particular, no existing studies have investigated the effect of injectable P4 on the fertility of cows subjected to FTAI. The aim of this study was to evaluate the pregnancy rate of lactating and non-lactating Nelore cows subjected to FTAI with injectable P4. Of the 422 non-lactating cows in this study, 162 (38.3%) became pregnant by 60 days post-FTAI. In the lactating group (n = 516), 166 (32.1%) were pregnant by 60 days after treatment with injectable P4. The proportions of lactating and non-lactating cows becoming pregnant were compared using the chi-square test, adopting a significance level of P < 0.05. It was found that the pregnancy rate of the cows subjected to FTAI with injectable P4 was influenced by lactation status. Lactating cows had lower reproductive performance, possibly because of their higher nutritional requirements. However, the use of injectable P4 shows promising results and may prove to be a useful strategy in large-scale livestock production. Key words: Injectable progesterone. Lactating cow. Non-lactating cows Synchronization of ovulation. Pregnancy rate. ResumoEm bovinos a maioria dos protocolos de inseminação artificial em tempo-fixo (IATF) utiliza a progesterona (P4) como base hormonal para a sincronização do estro. A utilização de uma fonte de P4 injetável para este controle do ciclo estral poderia ser uma estratégia farmacológica interessante, devido à praticidade de uma aplicação parenteral. O efeito da P4 injetável no controle da dinâmica folicular em bovinos tem sido pouco estudado, e até o momento, não há estudos que investigaram o efeito da P4 injetável na fertilidade de vacas submetidas à IATF. O objetivo do presente estudo foi avaliar a taxa de prenhez de vacas Nelore em lactação e não lactantes, submetidas a um protocolo de IATF a base de

This study evaluated the pregnancy rate in Nelore cows (Bos indicus) that were subjected to fixedtime artificial insemination (FTAI) using different protocols consisting of injectable progesterone (P4) or an intravaginal device (impregnated with P4). Multiparous cows 72-84 months in age, 30-45 days postpartum, were selected on the basis of the absence of a corpus luteum (CL) and follicles <8 mm after transrectal palpation and ultrasound examinations. On a random day of the estrus cycle (D0), the selected animals (n = 135) were randomly assigned to one of three experimental groups (n = 45 each). Group I (injectable P4/FTAI 36 hours) received 250 mg of injectable P4 and 2 mg EB on D0; on D7, they received 500 µg of cloprostenol; on D8, 300 IU of eCG and 1 mg of EB were administered; and finally, FTAI was performed 36 hours after the application of EB. Group II (injectable P4/FTAI 48 hours) received the same protocol as Group I, except that the FTAI was performed 48 hours after ovulation induction. The animals of Group III (Control/CIDR) received a conventional protocol for FTAI using an intravaginal device (D0: P4 and 2 mg EB; D8: device removal, 500 µg cloprostenol, 300 IU eCG, 1 mg EB; and FTAI performed 48 hours after removal of the device). The results showed that cows synchronized with the conventional protocol for FTAI (Control/CIDR) had a higher pregnancy rate (60 %, 27/45) than those synchronized with an injectable P4/FTAI 36 hours (33.33 %; 15/45, P = 0.010). However, the group receiving injectable P4 group/FTAI 48 hours had a similar pregnancy rate (48.9 %; 22/45; P = 0.290) when compared to both the group receiving the conventional protocol and that receiving injectable P4/FTAI 36 hours (P = 0.134). Although the injectable P4 may affect pregnancy rate with the FTAI performed in 36 hours, we found similar pregnancy rates from cows inseminated 48 hours after induction ovulation, considering injectable or intravaginal P4. Therefore, we suggest that injectable P4 represents an alternative source of progesterone for synchronization of cattle for FTAI. Key words: FTAI. Nelore. Injectable progesterone. Pregnancy rate. ResumoEste estudo avaliou a taxa de prenhez de vacas Nelore (Bos indicus) submetidas a diferentes protocolos de IATF a base de progesterona (P4) injetável ou dispositivo intravaginal impregnado com P4. Vacas multíparas entre 72 e 84 meses de idade, com 30 a 45 dias pós-parto foram previamente selecionadas com base na ausência de corpo lúteo (CL) e folículos < 8 mm após palpação e exame ultrassonográfico transretal. Em um dia aleatório do ciclo estral (D0), os animais selecionados (N = 135) foram aleatoriamente distribuídos em um dos três grupos experimentais (n = 45 / grupo). O grupo I (P4 injetável/IATF 36 horas) recebeu 250 mg de P4 injetável e 2 mg BE no D0. No D7 aplicou-se 500 µg de Cloprostenol. No D8 300 UI de eCG e 1 mg de BE foram administrados, sendo que a IATF foi realizada 36 horas após a aplicação do BE. O grupo II (P4 injetável/IATF 48 horas) recebeu o mesmo protocolo, excet...