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 CH emissions, and the size of synergistic effects for CH and nitrogenous emissions (NH and NO). 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 CH, CO, NH, and NO in incoming and outgoing air were measured. Cow excretion of organic matter was higher for CS compared with GS. Enteric CH and cow-associated NH and NO emissions (i.e., manure emissions excluded) were lower for CS compared with GS (-11, -40, and -45%, respectively). The CH and NO emissions from stored manure (i.e., in absence of cows) were not affected by diet, whereas that of NH emission tended to be lower for CS compared with GS. In conclusion, there was no trade-off between enteric and manure CH emissions, and there were synergistic effects for CH and nitrogenous emissions when grass silage was exchanged for corn silage, without balancing the diets for crude protein content, in this short-term study.