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A closer look at dietary energy Microbe types in the rumen include bacteria, archaea, proto- zoa and fungi. Many factors play into the mix found in a par- ticular cow’s rumen, such as age and health of the cow, her genetics, and most obviously, diet. How much energy is given in the diet, as well as the type of energy, can both affect rumen microbe function. Corn is a common energy source in the dairy cow diet in some countries, and it’s therefore useful for the dairy industry to know if different corn processing methods have any effect on rumen microbes. Steam-flaking of corn is a commonly-used processing method that increases digestibility. In heifers, a group of scientists from China recently found that steam- flaked corn (when compared to finely-ground corn) promoted increased abundance of amylolytic bacteria; this in turn increases the production of propionate, a metabolite involved in energy utilisation. Overall, it was found that heifers with increased propionate concentration exhibit relatively higher average daily gain. In another study, a group of researchers in China and the US also looked at how steam-flaked and finely-ground corn, as well amount of energy in the diet, affect rumen microbes in lactating dairy cows. Groups of study Holstein cows received treatments involving two levels of energy, low (LE, about 1.5 Mcal/kg) and high (HE, about 1.7 Mcal/kg), and two energy sources, GC (finely-ground corn) and SFC (steam-flaked corn) over 21 days. Previously, these scientists had found total-tract apparent di- gestibility, milk yield, milk protein content and yield, and milk lactose yield all increased with higher dietary energy, and SFC increased milk yield and milk protein yield. In this study, they found that “some microbial taxa and metabolic pathways were enriched by the HE level, and they might contribute to the improved lactation performance observed previously. Furthermore, because some of the microbial genera enriched by the HE diets had exhibited increased predominance in high-producing cows, they may be used as biomarkers of one or more of the lactation traits”. Future studies, say the scien- tists, are warranted. Guan notes that she and her colleagues “have so far identified the cattle DNA markers that relate to feed efficiency and ru- men microbes, and we predict that cattle with those markers may have better rumen efficiency which can be used for fu- ture breeding purposes”. However, whilst rumen microbiota are therefore heritable to some degree, it’s difficult to say at this point how much a particular biomarker might contribute to the expression of specific traits related to lactation or other processes.


Guan also explains that most of the research done on the ru- men microbiome draws conclusions on the relative abun- dance of bacterial species present in the rumen at one point in time. “However, rumen microbe populations can change even within even 24 hours,” she says. “So, the population level


64 ▶ GUT HEALTH | DECEMBER 2020


of a given microbe may be abundant relative to other species now, but not in a day, week or month. In addition, the chang- es in microbial abundance of a few species does not directly relate to metabolic functional changes. I think it’s too early to know if breeding of rumen efficiency will work in this way”.


Genetic analysis of the rumen microbiome Dr Andy Skidmore of Lallemand’s Technical Services team shares a similar view. He points to a study where the rumen microbiome was characterised in two cows, the rumen con- tents switched and then each microbe population reverted back to its original form 1 to 60 days later. “How can the mi- crobiome revert back so quickly after such a massive ex- change of rumen contents?” he asks. “There has to be some- thing else in the interaction between rumen contents and the host that significantly impacts the rumen microbiome”. Overall, he’s not sure how much we can significantly influ- ence the rumen microbiome and he believes that whilst its apparent stability may mean there’s a good opportunity to use genetic analysis of rumen microbes in dairy cow genetic selection for high rumen efficiency, it’s still very early days.


References available on request


PHOTO: RUBEN KEESTRA


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