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Induction of Subacute Ruminal Acidosis Affects the Rumen Microbiome
Subacute ruminal acidosis (SARA) negatively impacts the dairy industry by decreasing milk production, efficiency of milk production, and increasing culling rate and death loss. Six lactating Holstein cows were used in a replicated 2 × 2 Latin square design to determine the effects of SARA induction on the rumen microbiome. Experimental periods were 10 d with d 1 - 3 for ad libitum intake of control diet, followed by 50% feed restriction on d 4, and ad libitum access on d 5 of the control diet (control) or control diet + 4.6 kg of a 50:50 wheat/barley pellet (challenge). Ruminal samples were collected on d 1 and 6 of each period prior to morning feeding and separated into liquid and solid fractions. Bacterial DNA was extracted from the solid fraction after physical homogenization. Real-time quantitative PCR was used to determine SARA challenge effects on culturable bacterial species. Butyrivibrio proteoclasticus was observed in the greatest relative abundance of the evaluated species (0.4 - 0.2%) with a treatment × day effect (P < 0.01). For the control treatment, Butyrivibrio proteoclasticus increased (P = 0.04) from d 1 to d 6, but there was a tendency to decrease (P = 0.08) for the challenge treatment from d 1 to d 6. Anaerovibrio lipolytica remained stable during the challenge treatment, however, relative abundance increased (P < 0.01) decidedly on control d 6. A primary cellulolytic species, Fibrobacter succinogenes, was decreased (P < 0.02) from d 1 to d 6 of the control and challenge treatment. While Selenomonas ruminantium and Eubacterium ruminantium decreased (P ≤ 0.03) from d 1 to d 6 of the challenge treatment, both species were unaffected by control treatment. Relative abundance of Prevotella bryantii increased (P < 0.01) on d 6 of the challenge treatment, but no effects of the control treatment were observed. Similarly, the lactate-utilizing species, Megasphaera elsdenii, had a tendency to increase (P < 0.06) on d 6 of the challenge treatment, yet populations remained stable during the control treatment. Overall, results indicate the challenge treatment caused greater shifts within the rumen microbiome and are likely linked to the onset of SARA.
Keywords: acidosis, SARA, microbiome