ABSTRACT

-The objective of this experiment was to evaluate the effects of replacing eCG with FSH or FSH/LH on the diameter of ovulatory follicles (DOF) and the pregnancy rates (PR) of lactating Bos indicus cows subjected to a synchronization of ovulation protocol and fixed-time artificial insemination (FTAI) based on progesterone, estradiol benzoate (EB), PGF2α, and estradiol cypionate (EC). On day 0, primiparous and multiparous Nellore cows (n = 329) at 68 days postpartum were body condition scored (BCS) and received a P4 implant (PRIMER 1.0 g P4) plus 2 mg EB intramuscularly (IM). At day 8, the implant was removed, and 250 μg cloprostenol were injected IM along with 0.5 mg EC. At the time of implant removal, the animals were divided into one of four treatments: cows received (G1) 1 mL of saline solution IM (Control; n = 80); (G2) 300 IU eCG IM (ECG300; n = 84); (G3) 15 mg FSH IM (Folltropin; n = 82); and (G4) 30 IU FSH/LH IM (Pluset; n = 83); all cows were subjected to FTAI 48-54 h after implant removal (day 10). Transrectal ultrasonography was performed to measure the DOF to FTAI and to estimate the pregnancy rate on day 35. A statistical analysis examined the effects of the treatment, technician, semen, BCS, calf age and parity on PR to FTAI. There was no significant difference in PR and DOF among the treatment groups (G1, 41.3%, 13.1 mm; G2, 46.4%, 14.5 mm; G3, 46.3%, 14.2 mm; and G4, 48.2%, 14.3 mm), but PR was higher in multiparous than in primiparous cows. Commercial FSH solutions (Pluset or Folltropin) do not promote increases in PR or DOF of lactating Nellore cows and are equal to eCG in promoting growth in preovulatory follicles and elevating the PR in Nellore cows with a moderate BCS subjected to a progesterone-based FTAI protocol with EC.

Early weaning (EW) has been adopted in cattle breeding farms in Pantanal as a strategy to increase the rate of pregnancy in cows. The primary income of these properties is the production of beef calves, and the price of these animals depends on their weight. Therefore, the calves subjected to EW should present weight similar to or higher than those of calves subjected to conventional weaning (CW). This study aimed to evaluate the productive performance of pure (Nellore) calves and crossbred (Nellore/Angus) calves reared in the Pantanal and subjected to either EW or CW. After EW, the calves were supplemented with concentrate at 1 kg/animal/day (low-energy diet) or 1% of live weight (high-energy diet). The weights adjusted to 300 days of age were higher for EW calves fed the high-energy diet (p<0.01) in both genetic groups. No significant differences were observed in the weight of EW animals fed the low-energy diet and CW animals (p>0.01), and animal weight was 241.17 and 236.27 kg in crossbred calves and 184.44 and 189.78 in Nellore calves, respectively. The EW adopted in this experimental model did not affect the productive performance of calves raised in the Pantanal.

No abstract

The study aimed to evaluate the use of Melengestrol acetate (MGA) supplementation in protein-energy blocks on pregnancy rate post-FTAI or post-FTET for multiparous Nellore cows. In trial 1, 863 cows were submitted to FTAI following P4-estradiol protocol. After FTAI, the animals were allocated into three groups: control (n = 301): supplemented with nutritional blocks; MGA13-18 (n = 309): supplementation with same nutritional block added with MGA between the 13th and 18th days after FTAI; MGA6-18 (n = 253): supplementation with same nutritional block added with MGA between the 6th to 18th days after FTAI. In the second trial, 310 embryo recipients’ cows were submitted to the same estrus synchronization protocol and in vitro-produced embryos were transferred 7 days after the estimated estrus day (D0), and divided into two groups: control (n = 149): supplemented with nutritional blocks without the addition of MGA; MGA group (n = 161): supplemented with nutritional blocks added with MGA between 13th and 18th days after D0. In trial 1, the P/AI were similar for MGA13-18 (56.6%: 175/309) and MGA6-18 (57.70%: 146/253) groups, which were higher (P = 0.0273) than the Control (48.5%: 146/301). In trial 2, pregnancy rates weren´t influenced by treatments [Control: 49.33% (74/149); MGA: 54.37% (87/161); P = 0.185]. In conclusion, supplementation with MGA incorporated into nutritional blocks improves P/AI, proving to be a hormonal tool capable of increasing reproductive efficiency in cattle without major changes in animal supplementation management. The supply of MGA after FTET to recipient cows did not increase pregnancy rates.