Follicle stimulating hormone secretion and dominant follicle growth during treatment of Bos indicus heifers with intra-vaginal progesterone releasing devices, oestradiol benzoate, equine chorionic gonadotrophin and prostaglandin F2α

Progesterone release profile and follicular development in Nelore cows receiving intravaginal progesterone devices

This study aimed to evaluate the progesterone (P4) release profile provided by four commercially available intravaginal P4 devices, as well as the effect of circulating P4 concentrations exclusively from these devices on the development of the dominant follicle (DF) in Nelore (Bos indicus) cows. Therefore, non-lactating multiparous Nelore cows were enrolled in an experimental design, over three replicates, starting on Day -9 with the insertion of a reused P4 device (2 g - original P4 load) for 7 d, followed by two treatments of cloprostenol sodium (PGF; 0.482 mg), 24 h apart, on Days -3 and -2. Just before device removal, on Day -2, a norgestomet ear implant was inserted and, 2 d later (Day 0), at the time of norgestomet withdrawal, cows were randomly assigned to receive one of the intravaginal devices: Primer (0.5 g); Prociclar (0.75 g); Sincrogest (1 g); or CIDR (1.9 g), and 2 mg of estradiol benzoate (EB) im. Blood samples were collected immediately before P4 device insertion, 12 h later and daily over 15 d (1 d after P4 device removal). Ultrasound examinations were performed on Days 0, 7, 8, 9, 10, 12, and 14 to evaluate ovarian dynamics. Results are presented as mean ± SEM and differences were considered when P ≤ 0.05. Overall, the devices resulted in distinct circulating P4 concentrations over 10 d, varying according to their initial P4 load and P4 impregnated surface area. Primer provided the lowest circulating P4 concentrations over time, whereas, CIDR had the greatest concentration. Sincrogest and Prociclar were similar, producing intermediary circulating P4. There was no effect of treatment on the DF diameter on any specific day, nor on follicular growth rate from Day 7-10. However, the Primer device resulted in a greater mean DF diameter over time. Additionally, greater circulating P4 concentrations, mainly during the first 3 d of device insertion, were associated with smaller DF diameters regardless of the treatment. In conclusion, results from this study provided a better understanding of the P4 profile of intravaginal P4 devices, as well as, their effect on DF development in Bos indicus cows. These data contribute to optimize the use of P4 devices in the reproductive management of beef cattle.

Increased pregnancy rate in beef heifers resynchronized with estradiol at 14 days after TAI

We aimed to evaluate the treatment with estradiol benzoate (EB) or 17β-estradiol (E2) associated with progesterone (P4) for resynchronization of ovulation 14 days after timed artificial insemination (TAI). In Experiment 1 (Exp. 1), Nelore heifers were submitted to TAI (D0). On D14, the animals received an intravaginal P4 device and were randomly assigned to one of three groups: control (no treatment; n = 17); EB (1  mg EB; n = 17); and E2+P4 (1 mg E2 + 9 mg P4; n = 18). Ultrasonography evaluations were performed daily from D14 to D22 to map follicular and luteal dynamics. On D22, the P4 devices were removed and non-pregnant (NP) animals were determined using corpus luteum blood flow Doppler ultrasonography. In Exp. 2, 1295 beef heifers were resynchronized and randomly allocated to the same experimental groups as described in Exp. 1. On D22, the largest follicle (LF) was measured in NP and a second TAI was performed on D24. In a subset of heifers (n = 337), an estrus detection patch was used between D22 and D24 to monitor estrus expression and the LF was measured at D24. Confirmatory diagnosis of pregnancy was performed between D37-67 and D43-67 after first and second TAI, respectively. In Exp 1, the proportion of heifers with a synchronized follicular wave emergence (from 3 to 5 days after treatment) was greater (P < 0.05) in the EB group (93.8%) than in the control (62.5%) and E2+P4 (64.7%) groups. Structural luteolysis occurred earlier (P < 0.05) in the EB and E2+P4 groups than in the controls. The pregnancy rate after first TAI did not differ (P > 0.1) among the groups at D22 and at confirmatory diagnosis in both experiments. In Exp 2, the potential pregnancy loss between D22 and D37-67 was similar (P > 0.1) in the control (19% [36/185]), EB (15% [28/182]) and E2+P4 (15% [28/184]) groups. The LF diameter (mm) on D22 was greater (P < 0.05) in the control group (11.9 ± 0.1) than in EB (11.3 ± 0.1) and E2+P4 (11.5 ± 0.1). No difference (P > 0.1) was observed in the proportion of heifers detected in estrus, but LF growth rate (mm/day) between D22 and D24 was greater (P < 0.05) in EB group (0.9 ± 0.08) than in control (0.6 ± 0.07) and E2+P4 (0.7 ± 0.09) groups. The pregnancy rate for the second TAI was greater (P < 0.05) in the EB group (47% [94/200]) than in the control (37% [76/203]), but did not differ (P > 0.1) from the E2+P4 group (43% [93/214]). In conclusion, the treatment with 1 mg EB or 1 mg E2 + 9 mg P4 at 14 days post-TAI anticipates luteolysis in NP heifers but does not compromise pregnancy. The EB treatment induces a new synchronized follicle wave emergence and increases the pregnancy rate of resynchronized NP heifers.

A field investigation of a modified intravaginal progesterone releasing device and oestradiol benzoate based ovulation synchronisation protocol designed for fixed-time artificial insemination of Brahman heifers

Pregnancy rates (PR) to fixed-time AI (FTAI) in Brahman heifers were compared after treatment with a traditional oestradiol-based protocol (OPO-8) or a modified protocol (OPO-6) where the duration of intravaginal progesterone releasing device (IPRD) was reduced from 8 to 6 days, and the interval from IPRD removal to oestradiol benzoate (ODB) was increased from 24 to 36 h. Rising 2 yo heifers on Farm A: (n = 238 and n = 215; two consecutive days AI); B (n = 271); and C (n = 393) were allocated to OPO-8 or OPO-6. An IPRD was inserted and 1mg ODB i.m. on Day 0 for OPO-8 heifers and Day 2 for OPO-6 heifers. On Day 8, the IPRD was removed and 500 μg cloprostenol i.m. At 24h, for OPO-8 heifers, and 36 h, for OPO-6 heifers, post IPRD removal all heifers received 1mg ODB i.m. FTAI was conducted at 54 and 72 h post IPRD removal for OPO-8 and OPO-6 heifers. At Farm A, OPO-6 heifers, AI on the second day, the PR was 52.4% to FTAI (P = 0.024) compared to 36.8% for OPO-8 heifers. However, no differences were found between OPO-8 and OPO-6 protocols at Farm A (first day of AI) (39.9 vs. 35.7%), or Farms B (26.2 vs. 35.4%) and C (43.2% vs. 40.3%). Presence of a corpus luteum at IPRD insertion affected PR to FTAI (43.9% vs. 28.8%; P < 0.001). This study has shown that the modified ovulation synchronisation protocol OPO-6 may be a viable alternative to the OPO-8 protocol for FTAI in B. indicus heifers.

Utilização do dispositivo intravaginal de progesterona, em até três usos, para inseminação artificial em tempo fixo de fêmeas Bos indicus

Objetivou-se avaliar o efeito do número de utilizações (até três) do CIDRÒ, manifestação de estro e ordem de parição sobre a taxa de prenhez em vacas Bos indicus. Utilizou-se 1176 vacas pluríparas e primíparas, lactantes, 30 a 60 dias pós-parto. Os grupos receberam CIDRÒ de primeiro, segundo ou terceiro usos, mais 2,0 mg de benzoato de estradiol no dia de introdução (D0) e, 500 μg de dinoprost trometamina, 300 UI de eCG e 0,6 mg de cipionato de estradiol na retirada dos dispositivos (D8), com a IATF 48 horas após (D10). Em 30 dias realizou-se o diagnóstico de gestação (D40). Analisaram-se as variáveis pelo PROC LOGISTIC (SAS) e pela regressão logística binária, considerando-se significância quando p < 0,05. A quantidade de usos do implante influenciou a taxa de gestação (1 uso < 2 usos – p<0,05; 1 uso < 3 usos – p < 0,01; 2 usos = 3 usos; p > 0,1), de 44,8%, 51,1% e 51,1% para CIDRÒ 1, 2 e 3 usos, respectivamente, bem como a ordem de parição (pluríparas 50,85% > primíparas 34,48%; p<0,01), e manifestação de estro (com estro 44,02% > sem estro 33,06%; p<0,01). O CIDRÒ pode ser utilizado por até três vezes, mas as taxas de gestação mostram-se mais baixas no primeiro uso em relação ao segundo e terceiro usos e com melhores resultados em pluríparas e com manifestação de estro.