The objectives were to evaluate the effects of a 4-strain direct-fed microbial (DFM) on gastrointestinal tract (GIT) permeability and inflammation during feed restriction (FR) in heifers. Holstein heifers (n = 32; mean ± standard deviation; 295 ± 25 kg body weight; 287 ± 17 d of age) were used in an experiment conducted in 2 replicates (16/replicate). Heifers were randomly assigned to 1 of 2 top-dressed dietary treatments: (1) control (CON; 10 g/d dried lactose; n = 16) or (2) DFM containing a commercial blend of Lactobacillus animalis, Propionibacterium freudenreichii, Bacillus licheniformis, and Bacillus subtilis at 11.8 × 109 cfu/d (PRO; 10 g/d 4-strain DFM; n = 16). The trial consisted of 2 experimental periods (P): P1 (14 d) served as baseline for P2 (5 d), when all heifers were restricted to 40% of their P1 dry matter intake (DMI). On P1 d 12 and P2 d 2 and 5, GIT permeability was evaluated using oral chromium (Cr)-EDTA. By design, FR decreased DMI (60%) and body weight (∼18 kg) in all heifers. Regardless of treatment, during FR, all heifers had decreased circulating glucose, β-hydroxybutyrate, insulin, and l-lactate (4, 14, 45, and 19%, respectively), but increased nonesterified fatty acids, serum amyloid A, and haptoglobin (3.0-, 1.7-, and 5.0-fold, respectively). Circulating white blood cells, neutrophils, lymphocytes, and basophils decreased (4, 7, 5, and 6%, respectively), whereas eosinophils increased (41%) during P2 irrespective of dietary treatment. Circulating IFN-γ inducible protein-10 increased (23%) during FR compared with P1 regardless of treatment. Plasma Cr area under the curve increased in all heifers on d 2 and 5 (10 and 14%, respectively) of P2 relative to P1, but this was unaltered by dietary treatment. In summary, FR compromised GIT barrier function and stimulated an inflammatory response, but this did not appear to be ameliorated by PRO.
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