Dynamics of follicular growth and progesterone concentrations in cyclic and anestrous suckling Nelore cows (Bos indicus) treated with progesterone, equine chorionic gonadotropin, or temporary calf removal

Abstract

The objective of this study was to investigate the effects of eCG and temporary calf removal (TCR) associated with progesterone (P4) treatment on the dynamics of follicular growth, CL size, and P4 concentrations in cyclic (n = 36) and anestrous (n = 30) Nelore cows. Cyclic (C) and anestrous (A) cows were divided into three groups. The control group received 2 mg of estradiol benzoate via intramuscular (IM) injection and an intravaginal device containing 1.9 g of P4 on Day 0. On Day 8, the device was removed, and the animals received 12.5 mg of dinoprost tromethamine IM. After 24 hours, the animals received 1 mg of estradiol benzoate IM. In the eCG group, cows received the same treatment described for the control group but also received 400 UI of eCG at the time of device removal. In the TCR group, calves were separated from the cows for 56 hours after device removal. Ultrasound exams were performed every 24 hours after device removal until the time of ovulation and 12 days after ovulation to measure the size of the CL. On the same day as the CL measurement, blood was collected to determine the plasma P4 level. Statistical analyses were performed with a significance level of P ≤ 0.05. In cyclic cows, the presence of the CL at the beginning of protocol resulted in a smaller follicle diameter at the time of device removal (7.4 ± 0.3 mm in cows with CL vs. 8.9 ± 0.4 mm in cows without CL; P = 0.03). All cows ovulated within 72 hours after device removal. Anestrous cows treated with eCG or TCR showed follicle diameter at fixed-timed artificial insemination (A-eCG 10.2 ± 0.3 and A-TCR 10.3 ± 0.5 mm) and follicular growth rate (A-eCG 1.5 ± 0.2 and A-TCR 1.3 ± 0.1 mm/day) similar to cyclic cows (C-eCG 11.0 ± 0.6 and C-TCR 12.0 ± 0.5 mm) and (C-eCG 1.4 ± 0.2 and C-TCR 1.6 ± 0.2 mm/day, respectively; P ≤ 0.05). Despite the similarities in CL size, the average P4 concentration was higher in the A-TCR (9.6 ± 1.4 ng/mL) than in the A-control (4.0 ± 1.0 ng/mL) and C-TCR (4.4 ± 1.0 ng/mL) groups (P < 0.05). From these results, we conclude that eCG treatment and TCR improved the fertility of anestrous cows by providing follicular growth rates and size of dominant follicles similar to cyclic cows. Additionally, TCR increases the plasma concentrations of P4 in anestrous cows.

Influence of Follicular Growth Stimulation on Fertility of Beef Cows Treated with eCG or FSH in FTAI Protocols

“…Ainda segundo estes autores, entre os benefícios da administração do eCG em vacas de corte com baixa condição corporal estão a redução do anestro no pós-parto, maior crescimento folicular, maiores taxas de ovulação e de concepção. De outra forma, em rebanhos com melhor manejo e condição nutricional, este efeito positivo do eCG tende a não ser evidenciado [1,16].…”

“…O desmame por 48 h é normalmente recomendado para alcançar-se uma elevação de 5 a 10% na taxa de prenhez, quando comparada com os protocolos sem desmame temporário. Barreiros et al [1] relataram que tanto o tratamento com eCG como o desmame temporário por 48 h pode influenciar de maneira similar o crescimento folicular e a taxa de ovulação em vacas Nelore acíclicas. O desempenho reprodutivo dos programas de IATF com desmame temporário pode variar dependendo da ciclicidade ovariana das vacas, do intervalo parto-tratamento e do ECC [4,16].…”

“…No dia 0, foi inserido um implante intravaginal contendo 1 g de progesterona (DIB ® ) 1 , juntamente com uma injeção de 2 mg de benzoato de estradiol (Gonadiol ® ) 1 uma aplicação de 1 mg de benzoato de estradiol, i.m. A IATF foi realizada no dia 9, entre 52 e 56 h após a retirada do implante de progesterona.…”

“…O sucesso dos programas de inseminação artifi cial a tempo fi xo (IATF) depende do crescimento do folículo ovulatório (FO) e do controle da ovulação [1]. Na etapa fi nal do processo que precede a ovulação, o crescimento folicular está associado à maturação do oócito e, consequentemente, a sua capacidade fecundante [18].…”

“…O uso de eCG [1,6,12] ou FSH [16,17] no fi nal do tratamento para a sincronização do estro e da ovulação para IATF tem como objetivos: promover maior crescimento folicular, maior produção de estradiol e a maturação do oócito.…”