Impact of High-Concentrate Feeding and Low Ruminal pH on Methanogens and Protozoa in the Rumen of Dairy Cows

Department of Animal and Poultry Science, University of Guelph, Guelph, ON, N1G 2W1, Canada.
Microbial Ecology (Impact Factor: 3.12). 05/2011; 62(1):94-105. DOI: 10.1007/s00248-011-9881-0
Source: PubMed

ABSTRACT Non-lactating dairy cattle were transitioned to a high-concentrate diet to investigate the effect of ruminal pH suppression, commonly found in dairy cattle, on the density, diversity, and community structure of rumen methanogens, as well as the density of rumen protozoa. Four ruminally cannulated cows were fed a hay diet and transitioned to a 65% grain and 35% hay diet. The cattle were maintained on an high-concentrate diet for 3 weeks before the transition back to an hay diet, which was fed for an additional 3 weeks. Rumen fluid and solids and fecal samples were obtained prior to feeding during weeks 0 (hay), 1, and 3 (high-concentrate), and 4 and 6 (hay). Subacute ruminal acidosis was induced during week 1. During week 3 of the experiment, there was a significant increase in the number of protozoa present in the rumen fluid (P=0.049) and rumen solids (P=0.004), and a significant reduction in protozoa in the rumen fluid in week 6 (P=0.003). No significant effect of diet on density of rumen methanogens was found in any samples, as determined by real-time PCR. Clone libraries were constructed for weeks 0, 3, and 6, and the methanogen diversity of week 3 was found to differ from week 6. Week 3 was also found to have a significantly altered methanogen community structure, compared to the other weeks. Twenty-two unique 16S rRNA phylotypes were identified, three of which were found only during high-concentrate feeding, three were found during both phases of hay feeding, and seven were found in all three clone libraries. The genus Methanobrevibacter comprised 99% of the clones present. The rumen fluid at weeks 0, 3, and 6 of all the animals was found to contain a type A protozoal population. Ultimately, high-concentrate feeding did not significantly affect the density of rumen methanogens, but did alter methanogen diversity and community structure, as well as protozoal density within the rumen of nonlactating dairy cattle. Therefore, it may be necessary to monitor the rumen methanogen and protozoal communities of dairy cattle susceptible to depressed pH when methane abatement strategies are being investigated.

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    • "The pH of a given host environment acts as the primary immune defence through altering the resident microbiome environment (Hook et al., 2011; Ng et al., 2004; Urban and Mannan, 2014). "
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    ABSTRACT: The ability for protozoan parasites to tolerate pH fluctuations within their niche is critical for the establishment of infection and require the parasite to be capable of adapting to a distinct pH range. We used two host adapted Tritrichomonas foetus isolates, capable of infecting either the digestive tract (pH 5.3-6.6) of feline hosts or the reproductive tract (pH 7.4-7.8) of bovine hosts to address their adaptability to changing pH. Using flow cytometry, we investigated the pH tolerance of the bovine and feline T. foetus isolates over a range of physiologically relevant pH in vitro. Following exposure to mild acid stress (pH 6), the bovine T. foetus isolates showed a significant decrease in cell viability and increased cytoplasmic granularity (p-value <0.003, p-value <0.0002) compared to pH 7 and 8 (p-value > 0.7). In contrast, the feline genotype displayed an enhanced capacity to maintain cell morphology and viability (p-value > 0.05). Microscopic assessment revealed that following exposure to a weak acidic stress (pH 6), the bovine T. foetus transformed into rounded parasites with extended cell volumes and displays a decrease in viability. The higher tolerance for acidic extracellular environment of the feline isolate compared to the bovine isolate suggests that pH could be a critical factor in regulating T. foetus infections and host-specificity. Copyright © 2015. Published by Elsevier Inc.
    Experimental Parasitology 07/2015; 157. DOI:10.1016/j.exppara.2015.06.017 · 1.64 Impact Factor
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    Journal of Animal Science 04/2015; 93(4):1760. DOI:10.2527/jas.2014-8469 · 2.11 Impact Factor
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    • "Replacing fiber-rich roughage with starch-rich roughage has potential to reduce CH 4 emissions (Brask et al., 2013; Hassanat et al., 2013). Fermentation of starch favors the ruminal production of propionate at the expense of acetate and decreases rumen pH, which reduces hydrogen availability and activity of rumen methanogens (Van Kessel and Russell, 1996; Hook et al., 2011). The scientific evidence for this particular dietary replacement strategy is limited and does not always reflect diets used in practice. "
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