The use of industrial citrus wastes in dairy cattle nutrition: An in vitro approach on gas production and digestive parameters

This study was conducted to determine the effects of replacing corn grain with citrus pulp at 15% and 30% levels (on a dry matter basis) in total mixed rations on rumen fermentation, nutrient digestibility, microbial protein synthesis, and methane production. Nine ration groups (control (without additives), G15 (15% grapefruit), G30 (30% grapefruit), L15 (15% lemon), L30 (30% lemon), M15 (15% mandarin), M30 (30% mandarin), P15 (15% orange), and P30 (30% orange) were analyzed for chemical composition, in vitro gas and methane production, true dry matter digestibility, partitioning factor, microbial yield, microbial protein synthesis efficiency, neutral detergent fiber digestibility, organic matter digestibility, metabolizable energy, and net energy for lactation. Rations containing orange pulp, especially at the 30% level, produced the highest gas, metabolizable energy, and net energy for lactation values. Mandarin and lemon pulps supported balanced fermentation and higher fiber digestibility, while grapefruit pulp showed lower gas and methane production but higher partitioning factor, microbial yield, and microbial protein synthesis efficiency. Principal component analysis demonstrated that gas and methane production were linked to the first component, while digestibility parameters were associated with the second component. Hierarchical cluster analysis grouped the rations into four distinct clusters. Citrus by-products can therefore be considered sustainable feed ingredients: orange pulp as a rapidly fermentable energy source, mandarin and lemon pulps as balanced fiber-energy contributors, and grapefruit pulp as a fibrous feed with lower fermentation but improved microbial yield. The choice of citrus species and inclusion level should be optimized according to feeding goals, production performance, nutrient balance, and economic considerations.