PSXII-11 Maternal supplementation with guanidinoacetic acid and methionine: effects on arginine sparing, placental blood flow, and cow-calf performance.

Abstract Our aim was to assess whether maternal guanidinoacetic acid (GAA) supplementation, with or without rumen-protected methionine (RUP-Met) as a methyl group donor affects performance, plasma amino acid, and placental blood flow in pregnant beef cows during late gestation, and whether it impacts offspring performance. From day 202 of gestation until parturition, thirty-six Nelore cows (502 ± 12.8 kg) carrying female fetuses were randomly assigned to one of four treatments in a 2×2 factorial design: control (without inclusion of GAA and RUP-Met), RUP-Met (providing 0.02 g/kg BW of RUP-Met), GAA (providing 0.12 g/kg BW of GAA), and GAA+RUP-Met (providing 0.12 g/kg BW of GAA and 0.02 g/kg BW of RUP-Met). Body weight (BW) of the cows was taken at the beginning and end of the evaluation period. On days 232 and 267 of gestation blood samples were collected via jugular venipuncture and plasma was stored frozen at -20ºC for further analysis of amino acids. Simultaneously, approximately 50 mL of urine was collected by stimulated urination and stored at -80ºC for analysis of 3-methylhistidine. Uterine blood flow was evaluated at day 240 of gestation using Doppler ultrasound. At birth and weaning, calves from all treatments were weighed and kept with their dams under the same environmental and nutritional conditions. All statistical analyses were performed using the GLIMMIX procedure of SAS Studio and initial BW was used as a covariate when appropriate. Treatment effects were declared at P < 0.05. There was no treatment effect on cows’ voluntary intake (P = 0.44). Similarly, no treatment effect was observed in offspring performance (P = 0.79) and final BW of cows (P = 0.48). On the other hand, dietary GAA and GAA+RUP-Met had the lowest urinary concentration of 3-methylhistidine (corrected for creatinine), while the control treatment had the highest and RUP-Met showed intermediate values (P = 0.01). In contrast, dietary GAA and GAA+RUP-Met increased plasma concentration of arginine (P = 0.02) compared to other treatments. Glycine concentrations were highest in the GAA+RUP-Met treatment, being different from the control and RUP-Met treatment, while the GAA treatment showed intermediate values (P < 0.01). Conversely, dietary RUP-Met increased plasma methionine concentrations, with intermediate levels in GAA+RUP-Met treatment, and the lowest levels in control and GAA treatment (P < 0.01). A greater pulsatility index was observed in GAA treatment, followed by GAA+RUP-Met with intermediate values, and control and RUP-Met treatments showed the lowest values (P = 0.04). Supplementation of GAA alone or combined with RUP-Met as a methyl donor increases placental blood flow, spared arginine and reduce skeletal muscle catabolism in beef cows during late gestation. However, it does not affect offspring performance.