The role of prostaglandin F2α on ovulation and LH release in cows / A função da prostaglandina F2α na ovulação e na liberação de LH em vacas

This study aimed to evaluate the role of prostaglandin F2α (PGF) on ovulation. In Experiment 1, cows were randomly allocated to two treatments to receive 150 µg of d-Cloprostenol (PGF Group, n = 12) or 2 mL of NaCl 0.9% (Control Group, n = 11) and CIDRs, were removed 4 days later. No cow ovulated in Control and PGF groups. In Experiment 2, cows were randomly separated into two experimental groups to receive 4 injections of 150 µg of d-Cloprostenol (n = 9) or 2 mL of NaCL 0.9% (n = 9). In this experiment, ovulation was not observed in any cows. In Experiment 3, ovariectomized cows receive three injections of 300µg of PGF analog (PGF Group, n = 5), 100µg of Lecirelin (GnRH Group, n = 5) or 2 mL of PBS (Control Group, n = 4). The LH concentration was higher (P <0.0001) in cows from the GnRH group than in the PGF and Control groups. In experiment 4, cows with preovulatory follicles (>11.5 mm) were treated with Saline (Control Group, n = 6); Lecirelin (GnRH Group, n = 7) or Cloprostenol Sodium (PGF Group, n = 6). There was a significant increase in the vascular area of follicles from 0 to 24 h in GnRH and PGF treatments. In conclusion, PGF was not able to induce ovulation in cows with high or low plasma progesterone concentration. Additionally, PGF alone was not able to induce LH release and follicle luteinization, but increased follicular vascularization.(AU)

O objetivo deste estudo foi avaliar o papel da prostaglandina F2α (PGF) na ovulação. No Experimento 1, as vacas foram alocadas aleatoriamente em dois tratamentos para receber 150 µg de d-Cloprostenol (Grupo PGF, n = 12) ou 2 mL de NaCl 0,9% (Grupo Controle, n = 11) e os CIDR, foram removidos 4 dias depois. Nenhuma vaca ovulou nos grupos Controle e PGF. No Experimento 2, as vacas foram separadas aleatoriamente em dois grupos experimentais para receber 4 injeções de 150 µg de d-Cloprostenol (n = 9) ou 2 mL de NaCL 0,9% (n = 9). Não foi observada ovulação em nenhum dos animais deste experimento. No Experimento 3, vacas ovariectomizadas receberam três injeções de 300µg de análogo de PGF (Grupo PGF, n = 5), 100µg de Lecirelina (Grupo GnRH, n = 5) ou 2 mL de PBS (Grupo Controle, n = 4). A concentração de LH foi maior (P <0,0001) nas vacas do grupo GnRH do que nos grupos PGF e Controle. No Experimento 4, vacas com folículos pré-ovulatórios (> 11,5 mm) foram tratadas com solução salina (Grupo Controle, n = 6), Lecirelina (Grupo GnRH, n = 7) ou Cloprostenol Sódico (Grupo PGF, n = 6). Houve um aumento significativo na área vascular dos folículos de 0 a 24h nos tratamentos com GnRH e PGF. Em conclusão, a PGF não foi capaz de induzir ovulação em vacas com alta ou baixa concentração plasmática de progesterona. Além disso, a PGF sozinha não foi capaz de induzir a liberação de LH e a luteinização do folículo, mas aumentou a vascularização folicular.(AU)

Different protocols using PGF2α as ovulation inducer in Nelore cows subjected to estradiol-progesterone timed AI based protocols.

The objective of this study was to evaluate the effect of a PGF2α-analogue (PGF) on ovulation and pregnancy rates after timed artificial insemination (TAI) in cattle. In Experiment 1 cows received an intravaginal progesterone-releasing device (CIDR) plus 2 mg im of estradiol benzoate (EB) on Day 0. The CIDR devices were removed on Day 8, and all cows received 150 µg im of d-cloprostenol (PGF2α-analogue), 300 IU of eCG and 1 mg of estradiol cypionate (ECP) im. On Day 9, cows were randomly assigned into two groups: 1) ECP Group (n = 17), that did not receive any further treatment; and 2) ECP-PG Group (n = 14) that were given 150 µg of d-cloprostenol (PGF) as adjuvant stimulus for ovulation. No difference between groups was detected in interval for ovulation (P = 0.5), and in the proportion of cows ovulating (P = 0.09). In Experiment 2, multiparous suckling crossbred Aberdeen Angus cows (n = 260), were treated into two groups, similarly as Experiment 1; ECP group (n = 122), and ECP-PG group (n = 138). All females were TAI on Day 10. The proportion of cows treated with ECP that became pregnant was 54.9% (67/122), and cows treated with ECP plus PGF was 55.1% (76/138; P = 0.9). In Experiment 3, 686 Nelore cows, 40 to 50 days postpartum, were treated as Experiment 1 (ECP group), however, on Day 8 cows were divided into 3 groups: ECP Group (n = 216); PGF-SC Group (n = 228), in which cows did not receive ECP and were given an additional subcutaneous injection of PGF on Day 8; and PGF-IM Group (n = 242), in which cows also did not receive ECP on Day 8 and were given an additional injection of PGF im on Day 9. On Day 10, estrus was evaluated at timed AI (TAI). There was no difference in the diameter of the dominant follicle at CIDR removal and at TAI, and pregnancy per AI among groups (P > 0.05). However, the proportion of cows that displayed estrus between CIDR removal and TAI was higher in ECP group than in PGF-SC and PGF-IM groups (P < 0.001). Cows that displayed estrus has higher P/AI than cows that did not (P = 0.008). In conclusion, these results suggested that intramuscular or subcutaneous injection of PGF2α could be successfully used to induce ovulation in cattle undergoing TAI, with similar pregnancy rates when compared with ECP. The subcutaneous injection of PGF on the same day of CIDR removal could be an interesting alternative due it reduces cattle management to obtain similar results.