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Time-course of changes in select ruminal microbes during induction and recovery from diet-induced milk fat depression in dairy cows
Diet induced milk fat depression (MFD) results from bioactive fatty acids produced in the rumen during altered biohydrogenation, and changes in the rumen microbial population are commonly proposed as a key factor in development of the condition. An experiment was conducted to characterize the changes in select rumen microbes during induction and recovery from diet-induced MFD. Eight ruminally cannulated cows were used in repeated design and fed a low fiber, high PUFA diet (Induction; 29.5% NDF and 3.7% PUFA; DM basis) for a period of 21 d, and then switched to a high fiber, low PUFA diet (Recovery; 36.9% NDF and 1.1% PUFA) for 21 d. The control was the high fiber, low PUFA diet. We have previously reported decreased milk fat yield by d 7 and near maximal MFD by d 13 during induction, and a progressive increase in milk fat yield with full recovery by d 15. Ruminal digesta samples were collected 8 h after feeding on days 0, 4, 8, 12, and 20 and select ruminal microbes were quantified by Real-time PCR. Data were analyzed by PROC MIXED with the repeated statement and treatments compared at each time point. Treatment by time interactions were observed for most taxa (P < 0.05). Megasphaera eldesnii and S. ruminantium (lactate using bacteria) increased progressively >170% until d 12 of induction and decreased progressively during recovery. Streptococcus bovis (amilolytic bacteria) peaked at 350% higher than control on d 4 of induction (P < 0.01) and rapidly decreased during recovery. Prevotella bryantii (amilolytic bacteria) decreased 66% from d 8 to 20 of induction compared with the control and increased to control levels by d 12 of recovery. Ruminococcus albus (fibrolytic bacteria) and P. ruminicola (fibrolytic bacteria) were nearly constant during induction and recovery. However, F. succinogenes (fibrolytic bacteria) decreased 97% compared to control by d 4 of induction and increased progressively to an equal extent during recovery. The Butyrivibrio/Pseudobutyrivibrio group (t11-18:1 producer) decreased progressively during induction and increased during recovery, whereas the Butyrivibrio hungatei group (t11-18:1 producer) was not affected by treatment. Both ciliate protozoa and total fungi decreased progressively by >90% during induction and increased during recovery. Rapid adaptation of most of the observed microbes occurred during both induction and recovery from diet-induced MFD, and the time-course of adaptation matches the time-course of changes in biohydrogenation intermediates and inhibition of milk fat.
Keywords: Dairy cows, milk fat depression, ruminal microbes.