The effect of rumen-protected methionine and guanidinoacetic acid on growth performance, hematological indices, and immune-related gene expression in suckling Holstein Calves

This study evaluated the effect of rumen-protected methionine (RPM) and guanidinoacetic acid on performance, growth, hematological indices, and immune-related gene expression in suckling Holstein calves. Forty-eight Holstein calves (with an average weight of 39 ± 1 kg) were randomly divided into four experimental groups (<i>n</i> = 12). Each group randomly received one of four diets: (1) control, (2) a basic diet with 0.73% RPM, (3) a basic diet with 1000 mg of GAA acid, and 4) a basic diet with 0.73% PRM and 100 mg of GAA. Body weight (BW) was higher in the RPM group in comparison to the GAA group (<i>P</i> < 0.05). At day 56, glucose and cholesterol concentrations in calves receiving GAA, RPM, and mixed feeding were lower than in the controls (<i>P</i> < 0.05). The results demonstrated that the GAA and Mix groups experienced significant increases in IFN-γ gene expression (<i>P</i> < 0.05). In conclusion, RPM supplementation increased body weight compared to GAA, while GAA and RPM effectively reduced glucose and cholesterol levels at day 56. GAA also lowered cholesterol at weaning age compared to RPM. Significant increases in IFN-γ gene expression were observed in GAA and Mix groups.