Effects of ruminal dosing of Holstein cows with Megasphaera elsdenii on milk fat production, ruminal chemistry, and bacterial strain persistence

Authors: Weimer, Paul; CABRAL, LUCIANO - Federal University Of Mato Grosso; CACITE, FELIPE - Federal University Of Mato Grosso

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2015
Publication Date: 10/15/2015
Publication URL: https://handle.nal.usda.gov/10113/62004
Citation: Weimer, P.J., Cabral, L., Cacite, F. 2015. Effects of ruminal dosing of Holstein cows with Megasphaera elsdenii on milk fat production, ruminal chemistry, and bacterial strain persistence. Journal of Dairy Science. 98:8078-8092.

Interpretive Summary: Cows and other ruminants can digest very fibrous feeds because of bacteria and other microbes that essentially turn the rumen into a large fermentation vat. Past research has shown that Megasphaera elsdenii (M.e.) is a rumen bacterium that helps control rumen acidity on high-starch diets, but it may also contribute to milk fat depression which reduces the price a farmer receives for milk. In an attempt to more clearly understand the involvement of M.e. on milk fat depression, we dosed cows with strains of this bacterium, putting them directly into the rumen in an attempt to induce milk fat depression. In general, dosing did not induce fat depression, even when using bacterial strains isolated from the same individual cows during previous periods when they displayed milk fat depression. However, the dosed strains were generally reduced to very low population densities within 24 hours of dosing, suggesting that the dosed strains did not effectively compete with other rumen bacteria. The potential role of M.e. as a causative agent for milk fat depression remains unconfirmed and must await successful long-term establishment of dosed strains within the rumen. These results will be of use to researchers seeking to determine the role of M.e. in rumen metabolism.

Technical Abstract: Megasphaera elsdenii (Me) is a lactate-utilizing bacterium whose ruminal abundance has been shown to be greatly elevated during milk fat depression (MFD). To further examine this association, a total of 25 cannulated multiparous Holstein cows were examined in three studies in which strains of Me were directly dosed into the rumen (~2 x 1012 cells/dose); control cows were dosed with sterile lactate-free culture medium. Cows were fed a TMR (mean = 292 g starch/kg dry matter [DM]) that contained primarily corn silage, alfalfa silage, finely ground high-moisture corn, supplemental protein, and corn oil (3 g/kg DM). Studies differed in stage of lactation of the cows (middle or late), dosing events (single dose, or 4 doses over a 5-day period), timing of dose (pre-feed or 3-h postfeed), and Me strain (lab strain YI9 or 3 strains isolated from cows in the same herd). DM intake, milk yield, and composition were measured from 5 d to 0 d before dosing and 1 to 7 d after first dosing, plus later time points that varied by experiment. None of these measures were affected by dosing (P >0.05). Me was quantified in the liquid phase of ruminal contents by automated ribosomal intergenic spacer analysis, or by polymerase chain reaction (PCR) with relative quantification (Me 16S rRNA gene copy number as a percentage of total bacterial 16S rRNA gene copies). Neither the Me-dosed or control cows displayed MFD after dosing; in almost all cases, Me populations returned to low baseline levels (<0.02% of 16S rRNA gene copy number) within 24 h of dosing. This rapid decline in Me also occurred in several cows that were dosed with a strain that had been isolated from that particular cow during a previous bout of MFD. Ruminal pH, total mM volatile fatty acids (VFA), and mM lactate did not differ between dosed and control cows (P>0.05), although acetate:propionate ratio declined (P <0.01) in both groups, and butyrate increased after dosing with Me (P <0.05). The results confirmed that establishing exogenously added bacterial strains in the rumen is difficult, even for strains previously isolated from the recipient cow. The potential role of Me as an agent of MFD remains unclear in the absence of successful establishment of the dosed strains.