Dietary White Grape Pomace Silage for Goats: Assessing the Impact of Inclusion Level on Milk Processing Attributes

Grape pomace is the principal by-product of the winemaking industry, with an estimated global production of 14 million tonnes annually. Traditional livestock systems often incorporate local agroindustrial by-products into ruminant diets, and grape pomace is particularly notable for its high concentrations of bioactive compounds. These grape-derived molecules may exert beneficial effects on animal oxidative balance, biochemical status and productive performance, offering an environmentally and economically sustainable alternative to conventional feed ingredients that may be incorporated into the milk produced. This study evaluated the impact of incorporating varying inclusion levels (0, 5, 10 and 15% DM) of ensiled white grape pomace (WGP) into isoenergetic and isoproteic diets on the nutritional and technological characteristics of goat milk. Eighty-eight Murciano-Granadina dairy goats were selected and allocated into eight homogeneous batches (n = 11 per batch) based on physiological traits. Following a pre-experimental sampling, each diet was randomly assigned to two batches, and the feeding trial lasted eight weeks. After a two-week dietary adaptation period, four biweekly samplings were conducted to obtain representative bulk tank milk samples from each batch. Milk samples were analysed for gross composition, pH, mineral profile, fatty acid composition, coagulation properties, colorimetric parameters and antioxidant capacity. WGP consumption significantly increased milk fat content, improved the lipid profile from a human health perspective, accelerated curd aggregation and elevated the yellowness index. Moreover, notable changes were observed in the antioxidant activity of the milk. Despite these effects, the overall composition of the milk remained largely unchanged, which is a key factor in preserving its technological properties. Nevertheless, the final product demonstrated enhanced biological quality, reinforcing its value as a functional food for human consumption.