Effect of replacing dietary corn with beet pulp on energy partitioning, substrate oxidation and methane production in lactating dairy goats

The objective of this experiment was to study the effect of substitution of corn by beet pulp on energy partitioning, substrate oxidation, nitrogen and carbon balance and milk performance in dairy goats during late lactation. Twelve multiparous lactating Murciano-Granadina goats were fed two diets. Six goats were fed a mixed ration with 310 g/kg DM of ground corn (diet CORN) and in the other diet the corn was substituted with 302 g/kg DM of beet pulp (diet BP) in a cross-over design. No significant differences between diets were observed for milk production (1.36 kg/day, on average) and differences were found for milk fat (5.39 and 4.21% for BP and CORN, respectively). The metabolisable energy intake was higher (P < 0.05) in the CORN diet than BP (1320 vs 1044 kJ/kg0.75 BW, respectively). The difference in methane emissions between treatments was significant (P < 0.05) with values of 92 vs 61 kJ/kg0.75 BW for BP and CORN, respectively, indicating that greater levels of starch in diet reduce methane production. Replacing corn with BP reduced significantly the energy body fat deposition (300 vs 44 kJ/kg0.75 BW for CORN and BP diets, respectively). This reduction in energy retention for the BP diet did not compromise milk yield and milk energy output.