Enteric and manure emissions from Holstein-Friesian dairy cattle fed grass silage-based or corn silage-based diets

This study aimed to evaluate trade-offs between enteric and manure CH₄ emissions, and the size of synergistic effects for CH₄ and nitrogenous emissions (NH₃ and N₂O). Sixty-four Holstein-Friesian cows were blocked in groups of 4 based on parity, lactation stage, and milk yield. Cows within a block were randomly allocated to a dietary sequence in a crossover design with a grass silage-based diet (GS) and a corn silage-based diet (CS). The GS diet consisted of 50% grass silage and 50% concentrate, and CS consisted of 10% grass silage, 40% corn silage, and 50% concentrate (dry matter basis). The composition of the concentrate was identical for both diets. Cows were housed in groups of 16 animals, in 4 mechanically ventilated barn units for independent emission measurement. Treatment periods were composed of a 2-wk adaptation period followed by a 5-wk measurement period, 1 wk of which was without cows to allow separation of enteric and manure emissions. In each barn unit, ventilation rates and concentrations of CH₄, CO₂, NH₃, and N₂O in incoming and outgoing air were measured. Cow excretion of organic matter was higher for CS compared with GS. Enteric CH₄ and cow-associated NH₃ and N₂O emissions (i.e., manure emissions excluded) were lower for CS compared with GS (-11, -40, and -45%, respectively). The CH₄ and N₂O emissions from stored manure (i.e., in absence of cows) were not affected by diet, whereas that of NH₃ emission tended to be lower for CS compared with GS. In conclusion, there was no trade-off between enteric and manure CH₄ emissions, and there were synergistic effects for CH₄ and nitrogenous emissions when grass silage was exchanged for corn silage, without balancing the diets for crude protein content, in this short-term study.