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.

We evaluated the effect of supplementation with MGA incorporated into nutritional blocks on pregnancy rates (PR) after natural mating and AI of heifers and primiparous cows (Nellore) raised in extensive management. In exp 1, 413 heifers were grouped: control; Block-EB-P4; Block-MGA ; and Bran-MGA, and animals submitted to natural mating. In exp 2, 301 heifers were grouped: control; Block-MGA; and Block-MGA-EC, with animals inseminated after estrus observation for 10 days and, afterwards, mated with bulls. In exp 3, 342 primiparous cows, were divided into 4 groups: Control, Block-MGA-EB-eCG;Block-MGA-EB-CalfRemoval and Block- MGA-CalfRemoval, next, cows were mated with bulls. In exp 1, PR at beggining of breeding season was higher in the Block-MGA (57.84%; P < 0.01) in relation to Control (40.8%) and Block-BE-P4 (36.4%) and it was similar to Bran-MGA (51.0%). In experiment 2, PR at beggining of the BS in the control (56.6%; P = 0.04) was lower than in the MGA-EC (74.4%) and similar to the MGA group (67.7%). In exp 3, at 70 days (P = 0.01) and at the end of the BS( P < 0.02), respectively, the control (55%; 60.4%) had a lower PR than the groups MGA-EB-eCG (72.3%;75.9%;), MGA-EB-CR (74.1%;82.7%) and MGA-CR (74.4%; 81.3%). The results showed that use of MGA added to nutritional blocks in primiparous and heifers provided higher pregnancy rates at the beginning of the breeding season, and also higher PR in primiparous at the end of the season, representing an alternative for reproductive management under extensive conditions.