Effects of dietary forage-to-concentrate ratio on nutrient digestibility and enteric methane production in growing goats (Capra hircus hircus) and Sika deer (Cervus nippon hortulorum)

Objective: Two experiments were conducted to determine the effects of forage-to-concentrate (F:C) ratio on the nutrient digestibility and enteric methane (CH4) emission in growing goats and Sika deer. Methods: Three male growing goats (body weight [BW] = 19.0 +/- 0.7 kg) and three male growing deer (BW = 19.3 +/- 1.2 kg) were respectively allotted to a 3x3 Latin square design with an adaptation period of 7 d and a data collection period of 3 d. Respiration-metabolism chambers were used for measuring the enteric CH4 emission. Treatments of low (25:75), moderate (50:50), and high (73:27) F:C ratios were given to both goats and Sika deer. Results: Dry matter (DM) and organic matter (OM) digestibility decreased linearly with increasing F: C ratio in both goats and Sika deer. In both goats and Sika deer, the CH4 emissions expressed as g/d, g/kg BW0.75, % of gross energy intake, g/kg DM intake (DMI), and g/kg OM intake (OMI) decreased linearly as the F:C ratio increased, however, the CH4 emissions expressed as g/kg digested DMI and OMI were not affected by the F:C ratio. Eight equations were derived for predicting the enteric CH4 emission from goats and Sika deer. For goat, equation 1 was found to be of the highest accuracy: CH4 (g/d) = 3.36+4.71xDMI (kg/d)-0.0036xneutral detergent fiber concentrate (NDFC, g/kg)+ 0.01563xdry matter digestibility (DMD, g/kg)0.0108xneutral detergent fiber digestibility (NDFD, g/kg). For Sika deer, equation 5 was found to be of the highest accuracy: CH4 (g/d) = 66.3+ 27.7xDMI (kg/d)-5.91xNDFC (g/kg)-7.11x DMD (g/kg)+ 0.0809xNDFD (g/kg). Conclusion: Digested nutrient intake could be considered when determining the CH4 generation factor in goats and Sika deer. Finally, the enteric CH4 prediction model for goats and Sika deer were estimated.