Ruminal dosing with Megasphaera elsdenii and strain persistence are associated with milk fat depression in Holstein cows

Abstract Text:

The objectives of this study were 1) to examine the effects of ruminal dosing of cows with the bacterium Megasphaera elsdenii (ME) on milk fat production; and 2) to examine the persistence of the dosed species in the rumen.  Nine cows (51-201 days in milk, DIM) were divided into 3 groups balanced for DIM, milk production and milk fat content, and were fed the same TMR that contained corn silage, finely ground high-moisture corn, alfalfa haylage, corn oil and monensin.  The three treatments included ruminal dosing with pure cultures of one of two strains of ME (4257 and 5045, at an average of 1.9 x 10¹² cells/dose) recently isolated from milk fat-depressed cows, and a control dosed with sterile culture medium.  To encourage persistence of ME, ~40% of the ruminal contents from each cow were removed just prior to dosing, and 108 g of Na lactate was added for all treatments, on each of the 3 dosing days spaced 48 h apart. Milk production and composition were determined from 3x-daily milk samples collected from 8 d prior to first dosing to 21 d after first dosing, and ruminal fluid samples were collected for bacterial community analysis via 16 S rRNA metagenomics on the Illumina MiSeq platform. The dosing procedures resulted in a transient ruminal lactate concentration of up to 46 mM, and a subsequent decrease in acetate:propionate ratio (p<0.0001) as the lactate was metabolized. Both milk fat percentage and yield varied substantially by cow (p<0.001), and were decreased (p<0.01) during the week of dosing, when ME abundance was high. Data analysis of 112 ruminal samples  using PROC REG of SAS revealed a negative correlation between ME relative abundance and milk fat percentage in cows dosed with ME strain 4257 (r²=0.46, p<0.0001), but not in cows dosed with strain 5045 (r²=0.056, p=0.146). Control cows dosed with lactate but not an ME inoculum displayed weak negative correlation between milk fat percentage and ME abundance (r²=0.183, p=0.007), suggesting that the native ME populations were also associated with reduced fat content.  Similar results were observed for fat yield. Neither Propionibacterium acnes nor Eubacterium pyruvativorans were detected even in the most highly fat-depressed cows. The data confirm previous reports of a strong relationship between ME abundance and milk fat depression, but suggest that the effect may be ME strain-dependent.

Keywords: Megasphaera, Milk fat, Ruminal microbiome