Methane emission, ruminal fermentation parameters and fatty acid profile of meat in Santa Ines lambs fed the legume macrotiloma

Context Using legumes in ruminant production system may provide benefits such as improvement in animal performance and decrease in methane (CH4) emissions, mainly based on nutritional characteristics of these plants and the presence of tannins. Macrotiloma (Macrotyloma axillare) is a tropical legume that still lacks studies regarding its effects on animal performance and CH4 emissions. Aims The objective of this experiment was to evaluate productive performance, CH4 emission, ruminal fermentation parameters, carcass characteristics and fatty acid profile of the meat from lambs fed tropical grass hay supplemented with the legume forage macrotiloma. Methods For a 90-day experimental period, 14 Santa Ines male lambs (aging 100 days; 18.06 3.26 kg initial bodyweight) were allocated in individual pens and divided into two treatments: chopped aruana grass (Panicum maximum cv. Aruana) hay (CON); aruana hay supplemented with chopped macrotiloma hay at a ratio of 75:25 grass to legume (MAC). Lambs were weighed fortnightly for calculation of average daily bodyweight gain (ADG) and CH4 emission was measured on three occasions (days 28 to 32; 57 to 61; 85 to 89) using the sulfur hexafluoride (SF6) tracer technique. At the last day of CH4 collection, rumen fluid samples were collected for: determination of ammoniacal nitrogen (NH3-N) and short chain fatty acids (SCFA); ruminal protozoa count; and relative abundance determination of general bacteria (BACT); Ruminococcus flavefaciens (RUMI); Fibrobacter succinogenes (FIBRO); methanogenic archaea (METH) by real-time quantitative PCR (real-time-qPCR) analysis. Subsequently, after 16 h fasting, the animals were slaughtered; carcass characteristics were then evaluated and longissimus thoracis samples were collected for fatty acid profile analysis. Key results No significant difference (P > 0.05) was observed between MAC and CON for productive performance, CH4 emission, SCFA and carcass characteristics. Reduced protozoa count and relative abundance of METH were observed for MAC (P < 0.05). Conclusions Despite the lack of effects on productive performance and CH4 emission, the decreased relative abundance of METH and protozoa count indicated that macrotiloma may possibly present anti-methanogenic activity. Implications The inclusion of this legume in the diet of ruminants may affect rumen microbes and potentially decrease environmental impacts of the production system.