Energy expenditure and methane emissions of grazing dairy cows at two levels of pre-grazing herbage biomass

摘要

We quantified the effect of biomass on energy expenditure (EE), methane emissions (CH_4) and FPCMof grazing dairy cows. The experiment was carried out in November 2015. Treatments were two contrasting levels of pre-grazing biomass (LOWvs HIGH) at a dailyherbage allowance (DHA) of 30 kg DM (above 5 cm). Eight multiparous Holstein cows were used in a 2x2 Latin Square design. DMI was estimated using Cr,O_3and digestibility by faecal index (N and ADF). Grazing time was determined by observation between milking (9 hours). EE was estimated from heart rate and G>2 pulse, CH_4 was determined using the SF6 tracer technique. Pre-grazing herbage height and biomass above 5 cm differed significandy (48 vs 37 cm, P = 0.0374; 1,859 vs 1,447 kg DM ha~(-1), P = 0.05).However, DMI (18.3 kgd~(-1); P = 0.5101), grazing time (324 min; P ~ 0.6522), and EE (725.8 kj kg MW~(-1), P = 0.7986) did not differ among treatments. Therefore, FPCM and CH4 yield were similar (20.6 kgd~(-1),P = 0.7527; 21 gkgDM~(-1),P = 0.7115, respectively). In the current study, biomass in LOW was higher than intended which would explain the lack of difference in daily intake and EE at grazing.