Abstract
This study evaluated the effects of maternal supplementation of a Bacillus-based direct-fed microbial (DFM) on the plasma metabolome of cow-calf pairs. At the start of the study (day 0), 72 pregnant Brangus crossbred beef heifers (20 to 22 mo of age) were stratified by body weight (BW; 431 ± 31 kg) and body condition score (6.0 ± 0.36) and randomly allocated into 12 bahiagrass pastures (1 ha and six heifers/pasture). Treatments were assigned to pastures (six pastures/treatment) and consisted of heifers supplemented with 1 kg/head/d (dry matter basis) of soybean hulls, either alone (CON) or combined (BAC) with DFM containing a mix of Bacillus subtilis and B. licheniformis (Bovacillus; Novonesis, Hørsholm, Denmark) from day 0 to 242 (139 ± 4 d prepartum until 104 ± 4 d postpartum). Calves were weaned on day 242 and then allocated to drylot pens and fed the same diet until day 319. On days 271 and 287, calves were vaccinated against pathogens associated with bovine respiratory disease. Blood samples were collected from all heifers on days 0 and 63 (prepartum) and from all calves on days 271 (pre-vaccination), 274 (during the inflammatory response), and 287 (post-inflammatory response) to assess the plasma concentration of metabolites. There was a separation on day 63 (R2 = 0.96) for the plasma metabolome profile of BAC and CON heifers. Heifers fed BAC had increased (P ≤ 0.05) plasma concentration of 17 metabolites, including glycerophospholipids and amino acids, but decreased (P ≤ 0.05) plasma concentration of 4 triacylglycerols. Eight pathways related to amino acids metabolism were increased (P ≤ 0.01) in BAC vs. CON heifers. For the calf metabolome, a separation was observed on days 271 (R2 = 0.95), 274 (R2 = 0.95), and 287 (R2 = 0.99). Supplementation with BAC decreased (P ≤ 0.05) plasma concentrations of three and six metabolites from amino acids and triacylglycerols on days 271 and 274, respectively, and increased (P ≤ 0.05) plasma concentrations of 9, 10, and 28 metabolites associated with amino acids and lipids metabolism on days 271, 274, and 287, respectively. Maternal supplementation with Bacillus-based DFM altered calf amino acid metabolism before vaccination (P ≤ 0.03) but enhanced pathways associated with immune response after vaccination (P ≤ 0.05). Thus, maternal supplementation of a Bacillus-based DFM modified the maternal prepartum metabolome and the calf metabolome before, during, and after a vaccination-induced inflammatory response.