Corn supplementation during 41 days after the begginning of TAI protocol and its effects on metabolic hormones and reproductive performance of Nelore females

This study evaluates the effects of corn supplementation beginning at start of a TAI (D0) protocol until pregnancy check (D41) on metabolic hormones (Exp1) and reproductive performance of Nellore females (Exp1 and 2). On both trials TAI protocol was used according to Meneghetti et al. (Theriogenology,72,179-189,2009) and AI was performed on D11. On Exp1, 681 primiparous (P) cows with BCS 2.84 ± 0.36 and BW:407.12 ± 42.58 kg was used and blood samples was performed on D0, D11, D41 and D52 to evaluate IGF-1, leptin and GH concentrations. On Exp2, Nellore females (n = 2,395) were used, divided in twenty groups that included heifers (H, n = 648; four groups), P (n = 635; six groups) and multiparous (M; n = 1,112; ten groups) with BCS: 2.96 ± 0.36 and BW: 401.32 ± 50.06 kg). All P and M received resynchronization and second AI if they were open at the D41, and calves weaning weight was evaluated on Exp2. After calving, each group of cows was randomly assigned into two treatments: No Supplementation (NS) or supplementation with 1.0 kg/cow/day of corn from D0 to D11 and 2.2 kg/cow/day from D11 to D41 (CS). Both groups stayed on pastures with ad libitum access to water and mineral and TAI protocols started 35 days post calving. Continuous variables were analyzed using PROC MIXED and binomial variables using PROC GLIMMIX and PROC LOGISTIC, both from SAS. Lot was the experimental unit. On Exp1, there was interaction between treatment and day such that CS group had higher IGF-1 concentration on D11 (138.4 ± 2.2 vs 130.8 ± 2.1) and lower (P < 0.01) concentration on D41 (135.5 ± 2.2 vs 141.5 ± 2.1) compared to NS group. Also, CS increased (P < 0.01) the average of IGF-1 concentrations (140.3 ± 1.71 vs. 122.7 ± 1.81 ng/mL). Regardless of treatment, probability of pregnancy on D11 was positively correlated to IGF-1 on D11 (P = 0.02) and leptin (P = 0.02) and GH (P = 0.04) on D0 and negatively correlated to IGF-1 concentrations on D41 (P = 0.04). There was a positive linear effect of IGF-1 on D52 on probability of pregnancy at second AI (P < 0.01) and positive linear effect of IGF-1 on D11 on probability of final pregnancy rate (P < 0.01). On Exp2, there was no difference (P = 0.50) in TAI pregnancy rate between NS (50.97%) and CS (52.41%), but M cows had higher (P < 0.01) PR (56.62%) than H (47.99%) and P (50.46%) cows. Cows with BCS below 2.75 had lower (P < 0.01) PR (44.08% vs. 55.50%) compared to BCS 2.75 or more. Pregnancy rate at second AI tended (P = 0.10) to be higher in CS (44.25%) compared to NS (38.54%) cows. M cows had higher (46.22%) PR compared to P (36.57%) cows on second AI (P = 0.01). Final pregnancy rate was different (P < 0.01) between H, P and M cows (89.32%a, 71.74%b and 89.46%a) and there was an interaction (P < 0.01) between treatment and cow category: CS increased final pregnancy rate in P cows (77.81% vs. 65.68%) and decreased final PR in M (86.96% vs. 91.96%), with no effect on heifers (89.30%). Calves from CS P cows were heavier (P < 0.01) at weaning compared to NS group (207.79 ± 1.54 vs. 194.57 ± 1.73). M and P cows from CS group (425.31 ± 2.36 e 464.25 ± 1.81 kg) were heavier (P = 0.01) in the end of BS compared to NS (415.17 ± 2.47 e 457.83 ± 1.84 kg). In conclusion, corn supplementation for 41 days increased IGF-1 concentrations on first and second AI that was positively correlated to PR, increased PR to a second AI on P and M cows, increased final PR in P cows, decreased final PR in M cows; even thought, increased final breeding season M and P weight as well as increased calves weaning weight of P cows.