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Ruminal bacterial community composition: Cow specific?

Kurt Cotanch Published on 28 June 2012
red truck at feed bunk

Why do cows – rather rumens – behave differently on the same diet? We know that animal differences (i.e. age, parity, DIM, genetic potential) and management factors (i.e. crowding, time budgets, facilities) greatly affect production and animal health.

But even with paired animals fed the same diet, such as in our tiestall research trials, rumen pH and VFA profiles can differ drastically yet result in similar milk production. In some instances under similarly “controlled” circumstances, production and rumen parameters can vary.

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We recently experienced this variation in cow response in our sand-bedded Pen 30: High-production cows on a research trial were all fed the same diet.

Our herd was suffering from low milk fat and this group was the most notable exhibiting milk fat depression (MFD). Individual cows in this group ranged from extreme MFD with milk fat protein inversions to those producing normal levels of milk fat and protein. Same diet for all, so what was the issue?

This varied individual cow response reminded me of a research trial conducted at the USDA-ARS, U.S. Dairy Forage Research Center in Madison, Wisconsin, that could help explain such varied responses of cows to nearly identical feeding and management situations.

Their work involved exchanging rumen contents between cows and documenting changes in rumen pH, VFA profile and the composition of the rumen bacterial population (referred to as ruminal “bacterial community composition” or BCC). The research involved two experiments, using paired cows, that differed in their BCC as determined by means of genetic fingerprinting of the rumen bacterial population.

In Experiment 1, the average ruminal pH and VFA levels differed between the two cows (6.88 vs. 6.14 and 57 vs. 77 mM VFA, respectively), as measured at three hours pre-feeding over three days.

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Cows were each fed the same diet for the entire nine-week study. At day 0, rumen contents were emptied and exchanged between the two cows. After only 24 hours, rumen pH and VFA profiles returned to the level of – the cow.

In other words, Cow A received Cow B’s rumen contents, which originally had a pH of 6.88. Within 24 hours, Cow A, with her new rumen contents, had a ruminal pH that matched her original ruminal pH of 6.14 and vice-versa for Cow B.

The ruminal bacterial populations showed significant change to that of the new host cow BCC profile after 14 days and was nearly complete after 61 days.

Experiment 2 showed similar results with two different cows. It’s interesting to note that the ruminal pH and VFA levels returned to the host cows’ levels in spite of the delay in change of the ruminal bacterial populations. This indicates that the cow truly has the greater role in managing rumen pH and VFA levels than the rumen microbial population.

Through rumination, saliva production and rate of clearance of VFA, the cow significantly influences her own rumen chemistry. Certainly not a new concept, but I thought diet and the BCC would have had more influence in determining ruminal pH and VFA levels than is indicated with this study.

The fact that BCC is unique to individual cows and actually controlled by cows is intriguing. Clearly there is a unique relationship between the host cow and the rumen microbial population that results in host specificity.

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The significance of this can be seen in the failed attempts to modify ruminal microbial populations through the introduction of pure bacterial strains. This may also help explain the varied responses to other attempts at altering rumen fermentation through feed additives and rumen modifiers.

Cows simply have individualized and unique populations of bacteria in their rumens that may not all react alike. This concept should be considered when attempting to improve rumen fermentation through additives for improved digestive efficiency, nutrient utilization or possibly reduction of methane production.

What this has to do with our MFD, I’m not quite sure, other than it reminded me that cows and their rumen microbes are uniquely individual.

However, regarding our MFD, we have returned to about 3.8 percent fat, 3.2 percent protein for the whole herd. Not sure how, other than forage quality. It seems as though our MFD was a combination of events that may have included season (late summer/early fall), forage changes and the forage quality of feeding tails of silage piles.

We tried adding peNDF via straw, via 2011 first-cut grass silage replacing high-quality third-cut haylage, as well as decreasing unsaturated fats, all with minimal effects. In early November, we finally got deep into all of our forages and milk fat returned. Once again, forage quality or some other unknown? PD

References omitted due to space but are available upon request. Click here to email an editor.

—Excerpts from Miner Institute Farm Report, January 2012

PHOTO:Cows simply have individualized and unique populations of bacteria in their rumens that may not all react alike. This concept should be considered when attempting to improve rumen fermentation through additives for improved digestive efficiency, nutrient utilization or possibly reduction of methane production. Photo by PD staff.

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