There is no relationship between plasma amino acid concentration and urinary nitrogen concentration in heifers fed plantain or ryegrass.

The objective of this study was to investigate the relationship between plasma amino acid (AA) concentration and urinary nitrogen (N) concentration of dairy heifers offered cut plantain or perennial ryegrass-white clover pasture indoors. Twelve Jersey-Friesian heifers aged 9–10 months were equally assigned to two dietary treatments (plantain vs. perennial ryegrass-white clover pasture) in a completely randomised design. Urinary N concentration was lower in plantain fed heifers (1.4 g/kg) than in perennial ryegrass-white clover pasture fed heifers (3.4 g/kg). Feeding cut plantain or perennial ryegrass-white clover pasture did not have an effect on either plasma essential AA, non-essential AA or total AA. There was no association found between plasma AA concentration and urinary N concentration in the present study. Therefore, the urinary N concentration reduction in plantain fed heifers compared with perennial ryegrass-white clover pasture cannot be attributed by the differences in plasma AA. [ABSTRACT FROM AUTHOR]