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Title: Transient changes in milk production efficiency and bacterial community composition resulting from near-total exchange of ruminal contents between high- and low-efficiency Holstein cows

Author
item Weimer, Paul
item COX, MADISON - University Of Wisconsin
item DE PAULA, TANIA - Federal University Of Mato Grosso
item LIN, MIAO - Yangzhou University
item Hall, Mary Beth
item SUEN, GARRET - University Of Wisconsin

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2017
Publication Date: 8/14/2017
Citation: Weimer, P.J., Cox, M.S., De Paula, T.V., Lin, M., Hall, M., Suen, G. 2017. Transient changes in milk production efficiency and bacterial community composition resulting from near-total exchange of ruminal contents between high- and low-efficiency Holstein cows. Journal of Dairy Science. 100:7165-7182.

Interpretive Summary: Improving the milk production efficiency of dairy cows is essential to both the profitability and environmental sustainability of dairy farms. Cows that differ in milk production efficiency are known to have different rumen microbial communities, but a direct role of the microbial community in dictating efficiency is lacking. We demonstrated that near-total exchange of rumen contents between pairs of cows that differed in milk production efficiency resulted in a temporary change in their efficiency to more closely resemble the donor cow before gradually returning to the milk production efficiency of the host cow over a period of approximately one week. Likewise, the composition of the bacterial community reverted over about the same time period to that of the host cow. These results provide the first direct evidence that milk production efficiency can be altered, at least transiently, by substitution of the rumen bacterial community from a cow of different milk production efficiency. Future experiments will attempt to establish “high-efficiency” communities in cows by early-stage (birth through weaning) inoculations of rumen contents into calves, using rumen contents from high-efficiency cows. If successful, this strategy may be useful to dairy producers as a facile means of improving the profitability and environmental sustainability of their herds.

Technical Abstract: The objectives of this study were to determine if milk production efficiency (MPE) is altered by near-total exchange of ruminal contents between high- (HE) and low-MPE (LE) cows and to characterize ruminal bacterial community composition (BCC) prior to exchange and over time post-exchange. Three pairs of ruminally cannulated, third-lactation cows were selected whose MPE (energy-corrected milk [ECM] per unit dry matter intake) differed over their first 2 lactations. Approximately 95% of ruminal contents were exchanged between cows within each pair. Ruminal pH and volatile fatty acid (VFA) profiles, along with BCC (characterized by sequencing of the V4 region of 16S rRNA genes), were assessed just prior to feeding on days -8, -7, -5, -4, -1, 1, 2, 3, 7, 10, 14, 21, 28, 35, 42, and 56, relative to the exchange date. High-MPE cows had higher total ruminal VFA concentrations, higher molar percentages of propionate and valerate, and lower molar percentages of acetate and butyrate than did LE cows, and re-established these differences 1 d after contents exchange. Across all LE cows, MPE increased during 7 d post-exchange but declined thereafter. Two of the 3 HE cows displayed decreases in MPE following introduction of the ruminal contents from the corresponding LE cow, but MPE increased in the third HE cow, which was determined to be an outlier. For all 6 cows, both liquid- and solids-associated BCC differed between individuals within a pair before contents exchange. Upon exchange, BCC of both phases in all 3 pairs were more similar to that of the donor inoculum than to pre-exchange host BCC. For 5 of 6 cows, the solids-associated community returned within 10 d to more resemble the pre-exchange community of that host than to the donor community. Individual variability before the exchange was greater in liquids than in solids, as was the variability in response of bacterial communities to the exchange. Individual cows varied in their response, but generally moved toward re-establishment of their pre-exchange communities by 10 d after contents exchange. By contrast, ruminal pH and VFA profiles returned to pre-exchange levels within 1 d. Despite the small number of cows studied, the data suggested an apparent role for the ruminal bacterial community as a determinant of MPE.