The objective of this study is to evaluate the influence of postpartum body weight (BW), body condition score (BCS) changes and serum concentrations of Non-esterified Fatty Acids (NEFA) and Insulin-like Growth Factor 1(IGF-1) on reproductive performance of suckled Nelore cows submitted to timed artificial insemination (TAI). A total of 1950 lactating Nelore cows (1356 multiparous and 595 primiparous), were allocated into 17 groups of approximately 115 cows each. Groups were kept in individual Brachiaria brizantha or Panicum maximum pastures with ad libitum access to water and mineral salt. All groups were assigned to an estrus synchronization + timed AI protocol. In each group, cows were inseminated by 2 technicians and semen from 2 different Angus sires. Pregnancy status to first timed-AI were verified by detecting viable conceptus with transrectal ultrasonography (5.0-MHz transducer; 500V, Aloka, Wallingford, CT) 30 d after AI. Body Condition Score were evaluated by a single individual on each farm using a 5-point scale with 0.25 increments: 1 = thin to 5 = fat, on three times: time 1 = calving day; time 2 = at artificial insemination (AI), time 3 = 30 days after AI, on the pregnancy check diagnosis. Body weight were measured at three times: time 1 = approximately 3 weeks after parturition; time 2 = at artificial insemination (AI); time 3 = 30 days after AI. Blood samples were collected from 50% of cows, from either the coccygeal vein or artery into commercial blood collection tubes without anticoagulant, on the same moments as BW was evaluated. Blood samples were placed immediately on ice after collection, allowed to clot for 24h at 4°C, centrifuged at 1,000 × g at room temperature for 15 min for serum collection, and stored at -20°C. The samples will be analysed by Dr. Ky Pohler's laboratory located at the University of Tennessee Campus, Knoxville - TN. Non-esterified Fatty Acids (NEFA) and Insulin-like Growth Factor 1(IGF-1) will be analyzed by direct ELISA. The statistical models will be fitted using the Statistical Analysis System (SAS 9.4 for Windows; SAS Inst., Cary, NC), and Guide Data Analysis of SAS generated the regression models.
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