Watermelon Plant Silage: A Viable Alternative to Alfalfa Hay for Feeding Murciano-Granadina Goats

The study aimed to evaluate the nutritional value of watermelon plant silage (WPS) and to assess the effect of replacing alfalfa hay (AH) with WPS in a diet formulated for dairy goats. The study used four goats as donors of rumen microbiota to analyze in vitro fermentation parameters. The chemical composition analysis revealed that WPS and AH had similar protein content (21.1 vs. 18.9 g CP/100 g DM), but WPS had lower contents of organic matter (77.4 vs. 89.6 g/100 g DM), NDF (36.3 vs. 49.4 g/100 g DM), ADF (26.4 vs. 34.6 g/100 g DM), LAD (6.40 vs. 8.01 g/100 g DM), and amino acids (716 vs. 874 g AA/kg N) compared to AH. Conversely, WPS had higher fat content (3.09 vs. 1.29 g CF/100 g DM) and different macro- and micromineral content values than AH. In a first in vitro experiment, WPS and AH were incubated independently to compare their fermentation behaviour, indicating that the metabolizable energy (ME) tended to be higher for WPS compared to the AH diet (6.67 vs. 5.72 MJ/kg DM; p = 0.058). WPS fermentation produced lower concentrations of total VFA than AH (66.6 vs. 115 mM; p = 0.011), lower proportions of propionate and valerate (p ≤ 0.022), and higher proportions of isobutyrate (p = 0.001), without altering gas production (GP) kinetics as degradation rate and its potential release. In a second in vitro trial, a formulated goat diet (consisting of commercial concentrate and AH in a 1:1 ratio) was used as a control to assay the impact of AH replacing by WPS at 25% and 50% respectively. Trends were observed in several parameters, such as a linear increase in GP rate (p = 0.088), organic matter digestibility (p = 0.067), and CH4 concentration in the gas produced (p = 0.094) as AH was replaced by WPS. The study concluded that WPS could serve as a viable fodder to replace AH in conventional dairy goat diets while simultaneously reducing agricultural waste and serving as a regenerative model for implementing the circular economy strategy in the affected sectors.