Lactation performance of Holstein dairy cows fed diets with or without an annual forage mix silage

The use of annual forage mixes (sorghum-sudangrass, Italian ryegrass, and cool-season legumes) in dairy cropping rotations have increased, however research has not evaluated its use in dairy cattle rations and impacts on feed intake and milk production. Our objective was to compare the performance, nutrient digestibility, and gaseous emissions of lactating Holstein cows fed a diet containing either an annual forage mix silage (sorghum-sudangrass, Italian ryegrass, clovers) or an alfalfa-grass silage. Thirty-two primiparous Holstein cows (96 ± 38 d in milk) were stratified by days in milk then randomly assigned to one of two treatment diets (16 cows/treatment) containing either alfalfa-grass silage (Control) or annual forage mix silage (Mix) at 18.3% of diet dry matter (DM). Diets contained corn silage at 29.2% of DM with other ingredients balanced to achieve similar protein concentration. Cows were randomly assigned to individual feeding gates in 2 pens with diets fed to separate pens to avoid animal injuries at feeding. A 2-wk baseline period with all cows fed Control was followed by an 8-wk treatment period with cows fed assigned treatments. Dry matter intake (DMI) was affected by an interaction of treatment and time (P < 0.01) with Control having numerically greater DMI the first 4 wks, then Mix having numerically greater DMI thereafter. Cows fed Control produced more milk (P = 0.03) than Mix (38.0 vs 36.9 kg/d), however energy-corrected milk (ECM) yield was similar (40.8 vs 40.2 kg/d; P = 0.51). Efficiency of ECM production was similar the first 6 wks of study (P > 0.10); however, cows fed Control had improved ECM efficiency the last 2 wks (P < 0.05). Total-tract digestibility of DM and starch were greater for Control (P < 0.01), while Mix had greater neutral detergent fiber (NDF) digestibility (P < 0.01). Methane production (P = 0.02) and yield (P < 0.01) were lower for cows fed Mix (411 g/d and 15.2 g/kg DMI) than Control (450 g/d and 16.8 g/kg DMI). The use of Mix increased NDF content and digestibility, which compensated for lower starch and DM digestibility to allow for similar production. Based on these results, an annual forage mix harvested at a vegetative stage (70-100 cm height) would be suitable for use in lactating dairy cow diets. Appropriate diet formulation is needed to account for lower protein when sorghum-sudangrass makes up a significant part of the mix if replacing alfalfa-grass silage.