Enteric methane emission from growing yak calves aged 8–16 months: Predictive equations and comparison with other ruminants

Many prediction equations are available for enteric methane (CH₄) emission in cattle; however, these are not suitable for yaks, as CH₄ emission differs between these species. To our knowledge, no equation has been generated for yaks and, consequently, the aim of this study, at least in part, is to fill this gap. Feed and energy intakes, dry matter digestibility, and CH₄ emissions were measured in 16 yak calves (8 males and 8 females) at 8, 12, and 16 months of age. Concentrate (C) and forage (F) were offered the calves at a ratio of 60:40. There was no difference (P = 0.92) in body mass (m_b) between sexes, but there was a difference (P < 0.001) among ages. Significant differences (P < 0.001) were observed in the dry matter intake (DMI), organic matter intake (OMI), neutral detergent fiber intake (NDFI), acid detergent fiber intake (ADFI), gross energy intake (GEI), digestive energy intake (DEI), and metabolizable energy intake (MEI) among ages and between sexes. The CH₄ emission (g/d) and the energy equivalent of CH₄ emission (MJ/d) increased (P < 0.005) with increasing age, and they were higher (P < 0.005) in males than in females. There was no difference (P = 0.22) in CH₄ emission between sexes in g CH₄/kg DMI. Using simple linear regressions, DMI, OMI, and NDFI each explained 49–50% of the variation in CH₄ emission; whereas, GEI explained 49% of the energy loss due to CH₄ emission. In multiple regressions, NDFI and either m_b or ADFI explained 49–50% of the variation in CH₄ emission. It was concluded that CH₄ emission in yaks: (1) tended to be lower than emissions reported in the literature for cattle and Murrah buffalo calves fed diets of similar C:F ratios; and, (2) as in cattle, can be predicted by dry matter intake.