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 )

Two experiments were conducted to determine the effects of forage-to-concentrate (F:C) ratio on the nutrient digestibility and enteric methane (CH ) emission in growing goats and Sika deer. 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 3×3 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 CH emission. Treatments of low (25:75), moderate (50:50), and high (73:27) F:C ratios were given to both goats and Sika deer. 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 CH emissions expressed as g/d, g/kg BW , % 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 CH 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 CH emission from goats and Sika deer. For goat, equation 1 was found to be of the highest accuracy: CH (g/d) = 3.36+4.71×DMI (kg/d)-0.0036×neutral detergent fiber concentrate (NDFC, g/kg)+0.01563×dry matter digestibility (DMD, g/kg)-0.0108×neutral detergent fiber digestibility (NDFD, g/kg). For Sika deer, equation 5 was found to be of the highest accuracy: CH (g/d) = 66.3+27.7×DMI (kg/d)-5.91×NDFC (g/kg)-7.11× DMD (g/kg)+0.0809×NDFD (g/kg). Digested nutrient intake could be considered when determining the CH generation factor in goats and Sika deer. Finally, the enteric CH prediction model for goats and Sika deer were estimated.