Effects of addition of bacterial inoculants to the diets of lactating dairy cows on feed intake, milk yield, and milk composition

Forty-eight lactating Holstein cows (38 multiparous, 10 primiparous) were used in a 10-wk randomized block trial to determine the effect of 2 supplemental bacterial inoculants on DMI, milk yield, and milk composition. Experimental diets were top dressed with ground corn plus one of 2 bacterial inoculant mixtures. Treatments were control (no bacterial inoculant); 2 × 109 cfu/d of Propionibac-terium freudenreichii strain NP24 plus 1 × 109 cfu/d of Lactobacillus acidophilus strain NP51 (B1); and 2 × 109 cfu/d of P. freudenreichii strain NP24 plus 5 × 108 cfu/d each of L. acidophilus strain NP51 and strain NP45 (B2). Cows fed bacterial inoculants had greater yields of milk fat (P = 0.02), FCM (P = 0.007), and energy-corrected milk (P = 0.03) than did controls. Efficiency of milk production (defined as energy-corrected milk yield per unit of DMI) was greater (P = 0.03) for cows fed bacterial inoculants compared with control cows. There was no effect of treatment on DMI, milk fat percentage, or milk protein yield or percentage. There was a tendency (P = 0.08) for increased milk yield with inoculant supplementation compared with the control treatment. Serum urea N concentrations were greater for control cows compared with those receiving inoculants, and there was a tendency for B2 cows to have greater serum urea N concentrations compared with B1 cows. Results of this trial suggest that supplemental bacterial inoculants containing P. freudenreichii and L. acidophilus can improve milk yield and apparent efficiency of nutrient utilization.