Intestinal health challenges – including dysbiosis, inflammatory disorders, and pathogen susceptibility – impose severe economic losses and welfare concerns in intensive livestock production. Functional lipids, defined as bioactive lipid molecules with physiological benefits beyond basic nutrition, offer promising solutions to these issues. This review establishes a comprehensive definition of functional lipids and elucidates their metabolic process. Using short- and medium-chain fatty acid glycerides as a prime example, we examine their significant roles in energy homeostasis, gut microbiota composition and diversity, immune modulation, and antibacterial and antiviral activities. Additionally, we critically evaluate their current applications and future industrial potential in livestock production, providing evidence-based recommendations for their optimal implementation in animal nutrition strategies.

Probiotics represent a promising alternative to antibiotics in livestock production. This study investigated the effects of compound probiotic fermentation (FAM, comprising Lactobacillus acidophilus and Bacillus subtilis) on nitrogen utilization and nutrient digestibility in weaned piglets. A total of 180 piglets (28 days old; initial weight: 8.21 ± 0.67 kg) were allocated to three groups: control (basal diet), FAM (basal diet + 0.1% FAM), and antibiotic (basal diet + 55 mg/kg kitasamycin + 75 mg/kg chlortetracycline). After a 30-day trial, FAM supplementation significantly increased apparent nutrient digestibility of crude protein and ether extract, enhanced duodenal and jejunal digestive enzyme activities, and reduced fecal nitrogen excretion and serum urea nitrogen levels (p < 0.05). Serum metabolomics revealed that FAM upregulated metabolites linked to energy metabolism (e.g., creatine, L-carnosine), which are metabolites of amino acid metabolism, and enriched pathways such as amino acid biosynthesis and protein digestion. These findings demonstrate that FAM improves nitrogen utilization efficiency and gut health in piglets via biosynthesis and metabolism of amino acids, offering a viable alternative to antibiotics.

In vitro systems involving microbial fermentation typically require freshly obtained inocula, such as rumen fluid or faeces. The objective of this study was to test whether preserved faeces can be used instead of fresh faeces in the Hohenheim gas test (HGT). Fresh faeces from sheep (control, C) was compared with seven differently preserved faeces by using nine different feeds and studying in vitro gas production (GP) (n = 6–9 per treatment). Preservation involved freezing at −20°C (FR), shock-freezing with liquid nitrogen (N) and additional freezing at −20°C (FRN), FRN followed by defrosting (FRNdef), shock-freezing with liquid N and freeze-drying (FDN), freeze-drying (FD) and freeze-drying with storage for 3 weeks (FD3W) or 6 months (FD6M). Metaproteomics was used to analyse microbiome composition and function in treatments C, FR, FRN, FD, and FDN (n = 3 per treatment). On average across all feeds, the potential GP with FR and FRN (61 mL/200 mg DM) was comparable to that of C (62 mL/200 mg DM), whereas values for FRNdef, FDN, FD, FD3W, and FD6M were 85, 78, 76, 78 and 71% of C, respectively. All estimated GP kinetic parameters were affected by feed and preservation interactions (P<0.001). Microbiomes from C, FR, and FRN differed from those of FD and FDN based on the relative abundance of the core proteins (P<0.001). FD and FDN showed a significant decline of Bacteroidota, functional redundancy values, and specific proteins such as carbohydrate esterases (CE) (P<0.05) and glycoside hydrolases (GH) (P<0.01). Overall, frozen faeces closely resembled fresh faeces and can serve as a viable alternative inoculum source in the HGT. This may reduce animal numbers used for scientific purposes, but preservation and storage must be strictly standardised to maintain an active microbiome for GP-based in vitro tests.