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Two experiments in vitro were conducted to evaluate four Egyptian forage legume browses, i.e., leaves of prosopis (Prosopis juliflora), acacia (Acacia saligna), atriplex (Atriplex halimus), and leucaena (Leucaena leucocephala), in comparison with Tifton (Cynodon sp.) grass hay for their gas production, methanogenic potential, and ruminal fermentation using a semi-automatic system for gas production (first experiment) and for ruminal and post ruminal protein degradability (second experiment). Acacia and leucaena showed pronounced methane inhibition compared with Tifton, while prosopis and leucaena decreased the acetate:propionate ratio (P<0.01). Acacia and leucaena presented a lower (P<0.01) ruminal NH 3 -N concentration associated with the decreasing (P<0.01) ruminal protein degradability. Leucaena, however, showed higher (P<0.01) intestinal protein digestibility than acacia. This study suggests that the potential methanogenic properties of leguminous browses may be related not only to tannin content, but also to other factors.

Leucaena (Leucaena leucocephala), a leguminous shrub promising to cope with feed scarcity in the tropics, may help in mitigating ruminal methane (CH4) emission in the tropics as well. Two experiments were conducted to evaluate the effect of Leucaena and major secondary compounds of this plant in ruminants. At first, effects of Leucaena tannins and mimosine on ruminal CH4 and nutrient degradability were tested in vitro. Incubations were made with Leucaena without or with polyethylene glycol (PEG) to exclude the tannins effects, as well as with Bermuda grass (Tifton) and lucerne hays, both either untreated or supplemented with mimosine at the same concentration that has been provided by the tested Leucaena (6.52 mg/g DM). Furthermore, in an in vivo experiment a control diet (per kg DM 700 g Tifton hay) and Leucaena diets (per kg DM 350 g Tifton hay and 350 g Leucaena), either with or without 20 g PEG/d per head, were evaluated in six Santa Inês sheep following a double Latin square design. In vitro, Leucaena resulted in the lowest (p < 0.05) gas and CH4 production and the highest (p < 0.05) partitioning factor, a measure for microbial efficiency, whereas the amount of truly degraded organic matter (TDOM) was lowest (p < 0.05) with Tifton among the experimental forage plants. Mimosine addition to lucerne and Tifton as well as PEG addition to Leucaena had no effect on ruminal CH4 and TDOM. In vivo Leucaena, compared to the Tifton diet, enhanced (p < 0.05) intake, faecal nitrogen excretion, body nitrogen retention and the excretion of urinary purine derivatives as an indicator for microbial protein synthesis and availability. This was independent of PEG addition. Leucaena also decreased (p < 0.001) CH4 emission per unit of digested organic matter by 14.1% and 10.8%, without and with PEG, respectively. No significant diet differences were observed in total-tract nutrient digestibility. The study demonstrated efficiency of Leucaena to mitigate in vivo methane emission of sheep, but did not reveal which constituent of Leucaena was primarily responsible for that since no clear efficiency of either tannins or mimosine could be demonstrated.

Nitrate can be a source of NPN for microbial growth at the same time that it reduces ruminal methane production. The objective of this study was to evaluate the effects of 2 encapsulated nitrate products used as urea replacers on blood and rumen constituents, methane emission, and growth performance of lambs. Eighteen Santa Inês male lambs (27 ± 4.9 kg) were individually allotted to indoor pens and assigned to a randomized complete block design with 6 blocks and 3 dietary treatments: control (CTL) = 1.5% urea, ENP = 4.51% encapsulated nitrate product (60.83% NO3(-) in the product DM), and ENP+CNSL = 4.51% ENP containing cashew nut shell liquid (60.83% NO3(-) and 2.96% cashew nut shell liquid [CNSL] in the product DM). Diets were isonitrogenous with 60:40 concentrate:forage (Tifton 85 hay) ratio. The experiment lasted for 92 d and consisted of 28 d for adaptation (a weekly 33% stepwise replacement of CTL concentrate by nitrate-containing concentrates) and 64 d for data collection. The ENP and ENP+CNSL showed greater (P < 0.05) red blood cell counts than CTL. Blood methemoglobin (MetHb) did not differ (P > 0.05) among treatments, with mean values within normal range and remaining below 1.1% of total hemoglobin. There was an increase (P < 0.05) in total short-chain fatty acids concentration at 3 h postfeeding for ENP, with an additional increase (P < 0.05) observed for ENP+CNSL. No treatment effects (P > 0.05) were observed on acetate to propionate ratio. Methane production (L/kg DMI) was reduced (P < 0.05) with nitrate inclusion, recording 28.6, 19.1, and 19.5 L/kg DMI for CTL, ENP, and ENP+CNSL, respectively. Addition of CNSL did not result (P > 0.05) in further reduction of methane production when compared with ENP. Final BW, DMI, ADG, and feed efficiency were similar (P > 0.05) among treatments. Values for DMI were 1.11, 1.03, and 1.04 kg/d and for ADG were 174, 154, and 158 g for CTL, ENP, and ENP+CNSL, respectively. In conclusion, encapsulated nitrate products showed no risks of toxicity based on MetHb formation. The products persistently reduced methane production without affecting performance. Inclusion of cashew nut shell liquid in the product formulation had no additional benefits on methane mitigation.

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