This study investigated the dynamics of omega–3 long–chain polyunsaturated fatty acids (n–3 LCPUFA) in European fishponds, with a focus on the ecological and nutritional factors governing eicosapentaenoic acid (EPA, 20:5n–3) and docosahexaenoic acid (DHA, 22:6n–3) availability and poor accumulation in common carp ( Cyprinus carpio ). In a series of 9 experimental fishponds over one full vegetative season, we analyzed the food web and ecosystem processes. The carp gill–filterable plankton consortia (≥200 µm mesh) is a rich source of EPA+DHA: 1785.8± 479.3 mg 100 g −1 DM (annual mean), whereas the zoobenthos is a lesser–rich source: 622.7± 496.6 mg EPA+DHA 100 g −1 DM. Natural food is the only n–3 LCPUFA source for pond carp (as supplementary feed has 0%). Seasonal analyses showed a peak in lipid and n–3 LC PUFA availability during the early growing season (May–July), followed by their marked decline in the end season (August–October). Principal component analysis confirmed that these are tightly linked (positively correlated) with cladoceran abundance and negatively linked with chlorophyll–a concentration and fish biomass density. The EPA and DHA availability peaked at the beginning season, particularly during June–July (13.15± 3.40 µg EPA l −1 ; 5.72± 3.40 µg DHA l −1 ), while the lowest values (4.63± 5.27 µg EPA l −1 ; 2.04± 2.02 µg DHA l −1 ) were observed throughout the final three months before harvest or end season (August–October). The minimum physiological requirement of the essential n–3 fatty acid for carp, alpha–linolenic acid (ALA, 18:3n–3), was not fulfilled in the final three months before harvest (see supply–demand model). Final harvested carp in November showed 158.07± 3.79 mg EPA+DHA 100 g −1 wet weight (547.98± 102.64 mg 100 g −1 DM), indicating that merely 45% of EPA+DHA concentration factor was transferred from zooplankton-benthos DM to fish DM. Our findings indicate that the low EPA+DHA concentration in carp flesh is due to: (1) missing EPA and DHA in diet for three months before harvest, and (2) deficiency of essential ALA for three months before harvest. As a result, under present European pond feeding management, both accumulation and de-novo biosynthesis of n–3 LCPUFA in pond carp is severely compromised. Alternative feed and feeding management have been proposed.

Wine production generates large volumes of grape stems (GS), which are rich in fibre and phenolic compounds but have low digestibility due to their high lignin content. This study optimized alkali hydrolysis conditions to improve GS digestibility for ruminant diets using Response Surface Methodology (RSM) and a Box–Behnken design (BBD). Optimal conditions—90 °C, 2.08 h, and 33% solids—yielded a predicted in vitro organic matter digestibility (IVOMD) of 41.9%, representing an 42% increase compared to the untreated control (CTR) with 30.3%. Hydrolysis also modified fibre fractions and fermentation patterns. However, trade-offs included a reduction in total reducing sugars (TRS) and total phenolic compounds (TPC), which may lower antioxidant capacity (AOC). Despite these compositional changes, structural modifications enhanced fibre degradability, which supports the inclusion of GS as a functional feed ingredient. This approach promotes circular economy principles by upcycling winery by-products into sustainable livestock feed resources. • Grape stems, despite being rich in fibre and polyphenols, are often considered waste in winemaking. • Grape stems in animal feed is explored due to their beneficial fibre and polyphenols content. • High lignin content in grape stems can limit nutrient assimilation in animals • Alkali hydrolysis is a promising method to improve digestibility. • Optimal conditions for alkali hydrolysis to maximize digestibility include a temperature of 90°C, a duration of 2.08 hours, and a solids content of 33.0%.

The present study aimed to evaluate a unified model using fecal crude protein (CP) as a marker to estimate feed intake and digestibility in both cattle and sheep. The experiment involved five experimental periods with cattle fed with fresh Italian ryegrass ( Lolium multiflorum Lam.) in a two-year metabolism trial, evaluating three forage allowances: 15 and 22.5 g DM/kg body weight or ad libitum . Measured variables involved organic matter digestibility (OMD), organic matter intake (OMI), dietary crude protein (dCP), total fecal output, and fecal CP. In addition, a sheep dataset (n = 107) of Italian ryegrass intake at varying phenological stages was analyzed. Regression models (hyperbolic for OMD, linear for OMI, and dCP) were developed separately for each species and combined across species. Predicted values were compared with observed data using parallelism tests and relative predictive error (RPE). The combined cattle-sheep models for OMD, OMI, and dCP, showed R 2 of 0.72, 0.74, and 0.69 and RPEs of 6.4 %, 14.5 %, and 15.2 %, respectively, with no significant species effect. The fecal CP can effectively predict OMD, OMI, and dCP in both species grazing Italian ryegrass. Thus, the species-independent combined model provided reliable estimates. • Fecal crude protein (CP) can be used as a nutritional marker in sheep and cattle • Data from experiments with cattle and sheep feed Italian ryegrass were evaluated • A single mixed model based on fecal CP was tested to estimate digestibility and intake • A single mixed model can estimate the digestibility and intake in cattle and sheep