White grape pomace bale silage in dairy goat nutrition: productive, metabolic, and economic benefits of 15% dietary inclusion over a full lactation

This study evaluated the effects of including 15% DM of white grape pomace silage (15-WGP) in the diet of dairy goats on productive performance, nutritional efficiency, and metabolic responses. The experiment was conducted over an 8-month lactation period, during which economic performance was also assessed. Two isoenergetic and isonitrogenous diets (control and 15-WGP) were formulated, and 40 Murciano-Granadina goats were split and assigned to the 2 treatments, ensuring a balance regarding milk yield, SCC, parity and body weight, and also distributed into 4 homogeneous batches to record diet and water ingestion at batch level, ensuring balance across the selection criteria. After a pre-experimental sampling, the experiment began and data were collected individually on body weight evolution, milk yield, gross composition, and SCC every six weeks. Physiometabolic responses were evaluated through individual hematology and serum biochemical profiling at early, mid, and late lactation. Concurrently, plasma oxidative and inflammatory biomarkers were evaluated using ABTS, FRAP, SOD, and SAA assays. Statistical analyses of individual-level variables were performed using a mixed linear model (PROC GLIMMIX, SAS v9.4), including the effects of the pre-experimental covariate, diet, sampling time, the diet × sampling interaction, and batch nested within diet, with goat fitted as a random effect. A compound symmetry covariance structure was selected to account for the correlation among repeated measures, based on the lowest AIC and BIC values. Feed and water intake were monitored biweekly at the batch level, and a general linear model (PROC GLM, SAS v9.4) was applied, considering the effects of diet, sampling time, and their interaction. Least squares means were computed to interpret differences among levels of the fixed effects. Goats fed the 15-WGP diet showed no differences in DM intake compared with the control diet but exhibited significantly lower water intake and reduced milk urea content, while milk yield and body weight remained unaffected. Milk SCC and plasma cholesterol (CHOL) were higher in the 15-WGP group, although values remained within physiological limits. Total antioxidant capacity (ABTS) and specific antioxidant activity (SOD) indicated a significant improvement in oxidative status in goats receiving 15-WGP. The economic analysis revealed that the 15-WGP diet generated an additional net margin of €16/goat over the 8-month period. Overall, ensiled white grape pomace should be regarded as a valuable forage resource for dairy goat feeding.