Grass forages grown under identical conditions and conserved as silage or barn-dried hay: Effects on feed intake, performance, apparent total-tract digestibility, and fecal microbiota in dairy cows

Although high-forage diets benefit net human food production, cows' responses to differently conserved grass forages (ensiling vs. barn-drying) may affect feed intake and performance and eventually the efficiency of forage utilization. In the present study, forages were obtained from the same fields, harvested at the same time after equal wilting conditions, and either ensiled in a bunker silo or artificially dried in the barn. At the onset of the feeding trial, 18 lactating Holstein cows were divided into 2 feeding groups based on daily milk yield, BW, parity, and DIM. Cows received either grass silage (38% DM) or hay ad libitum for 35 d in addition to a fixed allocation of 3.64 kg DM dairy concentrate per cow and day. Data were collected for 21 d, after a 14-d adaptation period. Chemical analysis showed similar composition of NDF assayed with a heat-stable amylase and expressed exclusive of residual ash (521 and 524 g/kg DM), but differences in CP (136 and 117 g/kg DM) and water-soluble carbohydrates (WSC; 23 and 177 g/kg DM) between grass silage and hay, respectively. Results showed that cows fed hay had a significantly higher DMI (+2.4 kg/d) when compared with the group receiving grass silage, presumably due to microbial metabolites from ensiling, as well as lower content of WSC and NFC. Butyric acid, as well as the silage's low lactic acid content and uncommon lactic to acetic acid ratio, may have affected palatability and limited feed intake. Consequently, dairy performance was significantly higher, that is, 28.1 kg ECM/d versus 25.2 kg ECM/d in hay-fed cows versus silage-fed cows, respectively. Milk fat concentration was significantly higher in the hay group than in the silage-fed cows, with 4.37% and 4.06%, respectively. Body condition and apparent total-tract digestibility of nutrients remained unaffected by the treatment. Likewise, fermentation profile and bacterial community in feces were similar between groups. In conclusion, conserving grass forages as hay rather than silage maintains the level of WSC and can significantly increase feed intake and the resulting nutrient and energy supply to cows when concentrates are fed restrictively. In practice, this can help reduce concentrate feed usage per kilogram of milk, increasing net food production. Further research is needed to evaluate the effect of different conservation methods of grass forages in high-producing dairy cattle.