Day-to-day variation in trace and macro-mineral concentrations in corn and mixed grass-legume silages of Canadian commercial dairy herds

The aims were to assess the day-to-day variation in trace minerals (TM), macro-minerals, dry matter, and physical effectiveness factor in grass-legume and corn silages and to evaluate the variance partition. Grass-legume and corn silage samples were collected in 9 Canadian dairy herds during 2 episodes of 5 consecutive days at 4 weeks apart by the same individual. All variables were analyzed in duplicate. The proportion of variation due to the farm was more variable within TM than macro-minerals. Using TM software reference values of silages for formulating rations can lead to important errors. Except for physical effectiveness factor, the within-farm variations between sampling episodes were more marked for mixed grass-legume than corn silage. For most of the minerals and nutrients analyzed, the sampling + day-to-day variations were the main source of variability, accounting for over 50% of the within-farm variance for both silage types. The remaining within-farm variance was explained by subsampling and laboratory analyses. The high within-herd variation suggest that a silage sampling over more than one day can be useful to get a representative sample for TM analysis. Accurate nutrients and TM values when formulating cow diets is essential to cow health and productivity.