Effects of peripartal rumen-derived direct-fed microbial supplementation on lactation performance, metabolism, ruminal fermentation, and microbial abundance in dairy cows.

Direct-fed microbials (DFM) defined as “live, naturally occurring microorganisms that have been used to improve digestive function of livestock” are feed additives commonly used to improve production, efficiency and health in dairy cows.  Direct-fed microbials, by this definition, can be classified into three categories: bacterial, fungal, or a combination of both. Several benefits and modes of action have been proposed for DFM, including control of rumen pH driven by stimulation of lactic acid–utilizing bacteria, enhancement of rumen native microbiota by provision of growth factors, and improved nutrient uptake by increasing substrate breakdown. Despite the numerous proposed mechanisms, the specific modes of action of DFM are not fully understood and may vary depending on the type of microorganism used (e.g. bacterial or fungal), the dose and duration of administration, and the characteristics of the host animal and its microbiome. Several studies have reported positive effects of supplementing conventional DFM on the performance of dairy cows in the transition period, as well as in early lactation and mid-lactation. However, common bacteria and fungi used in conventional DFM are not native to the ruminal environment, and therefore they may have a limited ability to manipulate and interact with the rumen and its native microbial community. On rumen-derived DFM, though, limited data are available of their effects on performance, ruminal fermentation profiles and indicator blood parameters. Therefore, in the study cited, the objective was to evaluate the effects of rumen-derived DFM on performance, blood biomarkers, ruminal fermentation, and bacterial abundance in dairy cows during the transition period until 100 days in milk (DIM).

Fifty-six Holstein cows were enrolled in a randomized complete block design from −21 to 100 DIM. Cows were blocked based on expected calving date, parity, and previous lactation milk yield for multi-lactation cows or genetic merit for first-lactation cows. At −21 DIM, cows were randomly assigned to either a basal control diet supplemented with 150 g/day ground maize (CON; n = 29) or the control diet supplemented with ground maize plus a rumen-derived DFM product (GF; n = 27, 150 g/day ground corn + 5g/day) containing Clostridium beijerinckii at 1.0 × 107 cfu; Pichia kudriavzevii at 1.0 × 108 cfu; Ruminococcus bovis at 1.0 × 108 cfu; Butyrivibrio fibrisolvens at 1.0 × 108 cfu) that was top-dressed once a day. All cows received the same basal diet from −21 DIM until calving (1.56 Mcal/kg DM and 14.46% CP) and the same lactation diet from calving to 100 DIM (1.76 Mcal/kg DM and 15.69% CP). Blood samples were collected to measure biomarkers of metabolism, inflammation, and oxidative stress, as well as rumen fluid via oesophageal tubing for ammonia, VFA, and microbial abundance from a subset of multi-lactation cows (n = 12/treatment) at various time points from −22 to 100 DIM.

Compared with CON, GF cows produced more milk (+4.1 kg/day) during the immediate post-calving period (6–14 weeks) and tended to produce more milk (+2.9 kg/day) than CON during the entire trial (0–14 weeks). Although DMI was not affected by treatment, GF cows had greater feed efficiency (+0.18, milk/DMI) in the immediate post-calving period. Compared with CON, GF cows had lower blood plasma glucose and higher β-hydroxy butyrate (BHB). Blood biomarkers showed greater concentrations of ceruloplasmin, haptoglobin, and reactive oxygen metabolites (ROM) in GF cows. They also had greater ruminal molar proportions of butyrate and tended to have greater valerate and lower acetate. These changes in ruminal VFA were coupled with alterations in ruminal microbial abundance, where compared with CON, GF cows tended to have a greater abundance of lactate-utilizing species (Megasphaera elsdenii), but lower abundance of cellulose-utilizing species (Fibrobacter succinogenes). Although greater ROM was accompanied by a mild inflammatory condition in GF cows, this was not detrimental to milk yield and DMI.

Overall, our results suggest that supplementing GF in the transition period until 100 DIM positively affects lactation performance.