Validation and selection of nutritional markers to evaluate mixing quality in total mixed ration for dairy cows:...

Dairy cow diets can be categorized into three types: the formulated diet, the farm-prepared diet, and the diet consumed by cows. Aligning these diets requires monitoring the quality of the total mixed ration (TMR) to ensure consistency. However, limited information exists on nutritional markers to assess TMR homogeneity. We hypothesized that nutritional markers could monitor TMR mixing quality in ruminant diets. Therefore, this study aimed to validate a methodology, determine an appropriate coefficient of variation (CV), and identify the optimal marker to assess TMR mixing quality. TMR was sampled for five consecutive days on a commercial dairy farm, evaluating three diets (high-producing cows, mid-lactation cows, and dry cows). For each diet, three daily feedings were assessed, and in each feeding ten incremental samples were collected along the feed bunk immediately after feed delivery and before animal access. Ten equidistant sampling points were established. The marker was defined as the nutrient showing the highest residual variance among sampling points, with diet as a fixed effect and day and feeding as random effects. Residual variance proportions were: Potassium (99.1%), Crude protein (CP; 96.0%), Ether extract (95.7%), Zinc (94.3%), Phosphorus (93.0%), Neutral Detergent Fiber (NDF; 92.8%), Magnesium (91.3%), Manganese (81.9%), Iron (79.3%), Calcium (77.9%), and Sodium (77.4%). Magnesium was the most consistent marker (CV = 9.5%), while NDF and CP (CV = 9.04% and 9.27%) were also effective indicators of TMR mixing quality. These markers provide a practical approach to monitor TMR mixing quality and improve feed consistency in dairy production systems.