Rumen Fluid Transplantation from Allium mongolicum Regel-Fed Donors Enhances Lamb Meat Quality and Reduces 4-Alkyl Branched-Chain Fatty Acids

The extent of consumer approval for lamb is intimately connected to meat quality standards. Within this context, the distinctive ‘mutton taint’ serves as a critical benchmark for assessment, a characteristic that is largely governed by the concentrations of three fundamental branched-chain fatty acids (KBCFA), specifically 4-methyloctanoic acid (MOA), 4-ethyloctanoic acid (EOA), and 4-methylnonanoic acid (MNA). While Allium mongolicum Regel (AMR)—an Allium species prevalent in arid Asian regions known for its abundant bioactive constituents—is known to improve meat quality and mitigate these off-flavors, the potential mediating role of the rumen fluid in this process remains unclear. This study investigated whether rumen fluid transplantation (RFT) from AMR-fed donors could mimic the impacts of directly adding AMR to the diet on KBCFA accumulation and meat attributes. Thirty male lambs (23 ± 2 kg BW) were allocated at random into three distinct treatments (n = 10): a control set (CON), a dietary supplementation group administered 15 g/d of AMR (AMG), along with a rumen fluid transplantation treatment (RTG) inoculated with rumen fluid from AMR-fed donors. The carcass traits, physicochemical properties, and makeup of amino acids, as well as the fatty acid constitution of the longissimus thoracis muscle, were subjected to analysis. Data revealed that the levels of KBCFAs associated with off-flavors were markedly lowered in both the AMG and RTG. Specifically, decreases ranging from 49% to 64% were observed in MOA, EOA, and MNA concentrations (p < 0.05). Relative to the control group, drip loss and cooking loss were reduced in the treatment groups (p < 0.05), whereas ash (p = 0.047) and crude protein (p = 0.001) were increased. Moreover, the interventions improved the composition of essential amino acids (EAA), flavor-enhancing amino acids, and polyunsaturated fatty acids (PUFAs). In conclusion, rumen fluid transplantation effectively replicates the beneficial effects of dietary AMR on meat quality, particularly in reducing taint-related KBCFA. Such outcomes imply that rumen microbial communities likely act as a crucial mediator in controlling meat flavor.