Ronaldo Lucas

Contribution of condensed tannins and mimosine to the methane mitigation caused by feeding Leucaena leucocephala

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.

Effect of temperature and pre-incubation time of fibrolytic enzymes on in vitro degradability of Brachiaria (Brachiaria decumbens)

The ruminant production system in Brazil is based mostly on grazing and relies on native pastures and cultivated grass pastures. Improving forage digestibility is essential to overcome the energy loss and excessive nutrient excretion by livestock. Use of exogenous fibrolytic enzymes on tropical grasses has shown promise in increasing forage utilisation and productive efficiency of ruminants. The present study was taken up to evaluate the effect of temperature and pre-incubation time of cellulose-treated substrate (CTS) and xylanase-treated substrate (XTS) on in vitro degradability of Brachiaria decumbens substrate. Two commercial fibrolytic enzymes, cellulase and xylanase, were applied at the manufacturer’s recommended dose of 7.5 and 0.46 enzymatic units per 500 mg DM, respectively. Effect of temperature regimes of substrate exposure (18°C, 25°C and 32°C) and pre-incubation times with the enzymes (0, 12 and 24 h) were investigated in a complete factorial design. Three adult rumen-cannulated Santa Ines sheep served as inoculum donors. Substrates were incubated in vitro in semi-automatic gas production (GP) system and blanks were included for each inoculum. The GP was calculated, rumen degradability and volatile fatty acids (VFA) were determined. Interaction effect between temperature of substrate exposure and pre-incubation time with the enzyme was significant on degradable neutral detergent fibre (DNDF, g/kg) for both CTS (P = 0.01) and XTS (P = 0.04). Net gas production (GP, mL/g DNDF) of XTS (P = 0.06) differ on temperature versus pre-incubation time, whereas CTS were similar (P = 0.34). Partition factor, total VFA and acetate : propionate ratio were non-significant for both the enzymes. These findings highlight that Brachiaria may respond well to exogenous application of cellulase at all the environmental conditions studied and does not need any pre-incubation period.