Effects of dietary biochar supplementation in dairy cows on milk composition, processing characteristics, and butter quality.

This study investigated the effects of dietary biochar supplementation on raw milk characteristics and butter quality in German Holstein cows. Thirty-nine cows were assigned to 3 dietary treatments containing 0.0, 0.5, or 1.0% biochar (dry matter basis, included as part of the total mixed ration); 11 pre-designated primary cows per group were used for individual-level analyses, and 2 additional cows per group were maintained as reserve cows. Raw milk was collected before the start of supplementation (d-14), during the feeding period (d0, 35, and 70), and 14 d after supplementation (d70+14) to evaluate temporal responses and potential reversibility. Milk composition and physicochemical properties were analyzed, and milk was processed into butter to assess processing performance, color, moisture, and fatty acid composition. From a pooled sample, sensory and physicochemical attributes were analyzed. In an exploratory maximum-contrast comparison of the 0.0 and 1.0% groups, biochar supplementation affected raw milk composition, with increases observed in protein fractions, particularly casein and β-lactoglobulin, as well as a tendency toward higher milk fat content. In contrast, biochar had little to no effects on butter processing performance and butter quality parameters. Variations in churning time, butter yield, moisture, and instrumental color attributes were predominantly driven by sampling day and stage of lactation rather than biochar supplementation. Sensory evaluation of pooled butter samples revealed no adverse effects on flavor or odor perception, while moderate differences in color intensity and texture were observed, that were mainly associated with sampling day though. Overall, dietary biochar supplementation did not impair butter quality or sensory acceptance and correlated with increased protein and fat content in raw milk, the economically most relevant milk components. These findings indicate that biochar can be incorporated into dairy cow diets without negative effects on downstream dairy processing, while increasing key milk components important for butter production.