Abstract

This study investigated the effect of pasture and management system on nitrogen (N) pools related to N excretion in spot samples of urine in ewes grazing a hyper-diverse (>18 sown plant species) versus standard (perennial ryegrass + clover) pasture, managed under either contemporary (industry best-practise) or regenerative (high residuals, longer rotation length) management over a two-year period (Mar 2023-Dec 2024). A total of 160 Romney ewes were randomly allocated to four self-contained farmlets including standard pastures with contemporary management (Std-Con), standard pastures with regenerative management (Std-Reg), diverse pastures with contemporary management (Div-Con), and diverse pastures with regenerative management (Div-Reg) treatments. Urine samples were collected seasonally over two years. Results show that estimated urine volume was significantly (P=0.05) higher in ewes on diverse pastures (Div-Con: 5.19 L/d; Div-Reg: 4.97 L/d) compared to standard pastures (Std-Con: 3.79 L/d; Std-Reg: 3.52 L/d). Total urinary N output, (Purine Derivative: Creatinine ratio (PDC index), or the ratios of N, uric acid, allantoin, and urea to creatinine were not significantly affect by treatments. However, most parameters varied significantly across sampling times (P<0.01), indicating temporal effects related to physiological stage and seasonal variation in pasture quality. Overall, diverse pasture systems tended to support greater urine output and more consistent microbial protein supply (PDC index). Urinary metabolites were measured from a single urine spot sample collected within an existing grazing study and caution is still needed when using this method to avoid inaccuracies in estimating urinary metabolites due to variations between individual animals and studies.

Miyanda, M., Almeida A.K., Jonker A., Cartmill A.D., Sneddon N.W., Burkitt L., and Cranston L.M.

Hamilton, Volume 85, Hamilton, 55-60, 2025