Dairy cows are commonly fed direct-fed microbials (DFM) to improve milk production and efficiency. Most DFM are not native to the dairy cow rumen which may limit their ability to interact with the native microbiome. We evaluated the effects of two DFM supplements containing 4 native rumen microorganisms on the production of dairy cows. Ninety Holstein cows (92 ± 23 DIM, mean ± standard deviation (SD); 45 ± 10 kg milk/d; 658 ± 86 kg BW; 40% primiparous) were fed a common diet. After 14 d, they were blocked by parity, days in milk, and energy corrected milk (ECM) per unit of metabolic body weight. Within block, cows were randomly assigned to treatments, which were top-dressed daily for the next 112 d. Treatments were 150 g of ground corn mixed with 1) no live DFM (CON), 2) 5 g of a live DFM (Galaxis 2.0; G2), and 3) 5 g of a live DFM (Galaxis 2.0 Plus; G2P). G2 and G2P were products of Native Microbials Inc. (San Diego, CA) and contained the same organisms but in different concentrations. Supplementation with DFM did not alter yield of total milk, protein, or fat, but slightly decreased body weight gain and body condition score gain with no difference between G2 and G2P. DFM tended to decrease dry matter intake (DMI) but did not significantly improve feed efficiency (ECM/DMI). DFM did not alter digestibility of fiber, starch, protein, or fat, and did not alter concentrations of glucose or non-esterified fatty acids but tended to decrease concentration of insulin in plasma. DFM decreased somatic cell counts in milk with no difference between G2 and G2P. In conclusion, supplementation with native DFM had little impact on milk production and efficiency.
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