Thales Ricardo Rigo Barreiros

Taxa de prenhez de vacas Nelore lactantes tratadas com progesterona associada à remoção temporária de bezerros ou aplicação de gonadotrofina coriônica eqüina

This study aimed to evaluate the effects of temporary calf removal (TCR) or eCG administration on pregnancy rates of milking Nelore cows treated with a intravaginal progesterone releasing device (IPRD). In the first experiment 83 Nelore and 102 Nelore vs. Red Angus crossbred cows were randomly allocated to 3 groups. Animals in Group 1 (CON) received estradiol benzoate (EB; 2.5 mg, i.m., Estrogin®) and an IPRD (1g progesterone, DIB®) in a random stage of the estrous cycle (D0). At D9 the IPRD was removed and the animals were treated with d-cloprostenol (150µg, i.m., Prolise®). The animals were artificially inseminated (AI) 12 h after estrus detection. Group 2 (FTAI) was similar to CON, except that another dose of EB (1mg) was administered at D10, and 30-36 hours later artificial insemination (FTAI) was performed at a fixed time. In Group 3 (FTAI/TCR) the calves were removed from D9 to the FTAI. Pregnancy rates for Nelore and crossbred cows were, respectively, 7.69 and 41% (CON); 23.52 and 59.57 (FTAI); 69.44 and 55.81 (FTAI/TCR). In the second experiment, 255 lactating Nelore cows were allocated to 3 groups. At D0, animals in Group 4 (FTAI) received EB (2 mg) and one IPRD (1.9g progesterone, CIDR-B®), which was removed at D8 when the cows received 25 mg of dinoprost (i.m., Lutalyse®). At D9 EB (1 mg) was administered and 30-36 hours later all animas were FTAI. In Group 5 (FTAI/TCR) the calves were removed from D9 to FTAI. The Group 6 (eCG) was similar to IATF except for the administration of eCC in D9 (400 IU, i.m., Novormon®). Pregnancy rates were: 50.57% (FTAI), 53.57% (FTAI/TCR) and 54.76% (eCG). These results indicated that TCR associated with IPRD increase pregnancy rates, whereas the addition of eCG to IPRD do not improve pregnancy rates in Nelore cows which are cycling and in lactation with good body condition.

High numbers of antral follicles are positively associated with in vitro embryo production but not the conception rate for FTAI in Nelore cattle.

The objective was to compare the conception rates for FTAI and in vitro embryo production between Nelore cows with different antral follicle counts (AFC=number of follicles ≤3mm in diameter in the ovaries). Nelore cows (n=547) were subjected to ovulation synchronization. Randomly during the estrous cycle (D0), cows received an intravaginal device containing 1.9g P4 (CIDR(®)) and 2mg BE (Estrogin(®)), IM. When the device was removed (D8), the cows received 500μg PGF2α (Ciosin(®)), 300IU eCG (Novormon(®)) and 1mg EC (ECP(®)), IM. All cows were inseminated 48h after P4 device removal. Antral follicles ≥3mm were counted using an intravaginal microconvex transducer (D0), and the cows were assigned to high (G-High, ≥25 follicles, n=183), intermediate (G-Intermediate, 16-20 follicles, n=183) or low AFC groups (G-Low, ≤10 follicles, n=181). In another experiment, COCs were retrieved by OPU from Nelore cows (n=66), which were assigned to groups according to oocyte production: G-High (n=22, ≥40 oocytes), G-Intermediate (n=25, 18-25 oocytes) or G-Low (n=19, ≤7 oocytes). All COCs from the same cow were cultured individually (maximum of 25 COCs per drop) and then in vitro fertilized using thawed frozen sperm (2×10(8)/dose) from a Nelore sire of known fertility. The data were analyzed using a Kruskal-Wallis and a Chi-square test (P≤0.05). There was no difference in the conception rates after FTAI between Nelore cows with high, intermediate or low AFC (51.9 vs. 48.6 vs. 58.6%). The number of viable embryos was 18.4±6.7 (G-High), 6.1±3.6 (G-Intermediate) and 0.6±0.7 (G-Low; P<0.05). Therefore, AFC had no influence on the conception rates for FTAI; however, Nelore cows with high oocyte production exhibited better in vitro embryo production.

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

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.