Lactation performance and rumen fermentation profiles of dairy cows fed different corn silage hybrids ensiled with or without microbial inoculant

A lactation study was conducted to examine the effects of a silage inoculant (SI; Lactobacillus bucherni) applied, at ensiling, onto conventional (CCS) or brown midrib corn silage (BMR). Lactational performance and rumen fermentation of dairy cows were measured. Forty multiparous Holstein cows were used, starting at 20-58 days in milk (DIM), in a completely randomized design with a 2 x 2 factorial arrangement of treatments. Cows were randomly assigned to one of 4 diets; CCS TMR without SI (CCS-SI), CCS TMR with SI ( CCS+SI), BMR without SI (BMR-SI), and BMR with SI ( BMR+SI). The study lasted a total of 10 wk (2 wk of adaptation and 8 wk of data and sample collection). The SI (Agmaster(TM) XV, DuPont, Waukesha, WI) was applied at 1.25 x 105 cfu/g of corn crop at time of ensiling. Cows fed BMR increased dry matter intake (DMI) compared to those fed CCS (28.7 vs. 25.5 kg/d; P < 0.01), but SI did not affect DMI. Milk yield tended to increase for BMR treatments over CCS treatments (46.1 vs. 42.8 kg/d; P = 0.07). In contrast, milk fat yield tended to increase (P = 0.08) due to feeding BMR, also causing a tendency for increased energy corrected milk (ECM) yield by feeding BMR (46.8 vs. 44.7 kg/d; P = 0.10). Dietary treatments did not influence concentrations of milk protein and milk urea nitrogen (MUN). Digestibility of dry matter (DM) was increased for BMR treatments (P = 0.09), whereas feeding BMR increased (P < 0.01) digestibility of neutral detergent fiber (NDF) and acid detergent fiber (ADF). Rumen pH averaged 6.29 across treatments and did not differ. Total concentration of volatile fatty acids (VFA) was not affected by dietary treatments. Feeding BMR increased (P < 0.01) molar proportion of acetate and decreased (P < 0.01) molar proportion of propionate, resulting in an increase in the acetate-to-propionate ratio (P < 0.01). Applying SI did not influence VFA profiles. Ammonia-N (NH3-N) concentration was similar in response to dietary treatments. Our conclusions are that the SI tested in this study did not affect lactation performance or rumen fermentation and cows fed BMR increased yields for milk yield, milk fat, and ECM due to increased fiber digestion and rumen acetate production.