Effects of White Grape Pomace Silage on Milk Yield and Economic Return in Murciano-Granadina Goats Over a Full Lactation.

Within the UN's Sustainable Development Goal strategy for 2030, the valorisation of by-products and the reduction of inputs to produce high-biovalue food are priorities. Dairy goats contribute significantly to the sustainable conversion of fibrous biomass into high-quality food products for human consumption. At the same time, feed accounts for the highest expenditure on livestock farms. Therefore, incorporating agro-industrial by-products such as white grape pomace into ruminant diets could reduce feeding costs while improving the circular economy. This study evaluated the effects of incorporating white grape pomace silage (WGPS) at 15% of dietary dry matter in the diet of lactating dairy goats on milk yield and composition. The experiment was conducted over an eight-month lactation period and included an economic assessment. Two isoenergetic and isoproteic diets (Control and WGPS) were formulated and randomly assigned to 40 Murciano-Granadina goats, distributed into four groups (2 diets × 2 replicates) balanced by productive performance. At six-week intervals, batch-level samples were collected to assess dry matter (DM) and water intake, while individual measurements were taken for body weight, milk yield, milk composition, and somatic cell count. Variables were analysed using a mixed linear model (PROC GLIMMIX, SAS v9.4), accounting for the effect of the pre-experimental covariate, which proved significant in all cases except for feed efficiency. Goats fed the WGPS diet showed slightly lower DM and water intake and reduced milk urea concentration, without impacting milk yield or body weight. The economic analysis revealed that WGPS inclusion led to an additional margin of EUR 16 per goat over the eight months compared to the control group. It is concluded that white grape pomace silage is a viable forage option for inclusion in dairy goat diets.