The variation in feed efficiency among dairy cows is due to differences in fermentation and digestion characteristics, but recent studies have suggested that various aspects of postabsorptive metabolic processes including heat production or the metabolizable energy for maintenance are more crucial. Thus, metabolic efficiency largely determines feed efficiency, but whether divergent feed efficient cows differ in O2 consumption and metabolic CO2 production, directly determining the metabolic rate has not been investigated. Therefore, the objective of the present study was to determine whether variation in ME intake (MEI), O2 consumption, and metabolic CO2 production account for the variation in metabolic efficiency of dairy cows and whether this effect persists across the lactation cycle. Eighteen cows with different German breeding value functional herd life were kept in freestalls with ad libitum access to a total mixed ration that was kept constant in composition throughout the first lactation. Cows were blood sampled and weighed at wk 5, 13, and 42 postpartum (pp) and transferred into respiration chambers. Animals were retrospectively clustered according to MEI, O2 consumption, and metabolic CO2 production, each normalized to metabolic body weight (mBW). Cluster analysis revealed 9 high metabolically efficient (high-Meff) and 9 low metabolically efficient cows. The high-Meff cows had greater MEI and feed conversion efficiency, produced less metabolic CO2 and methane, had a stronger negative energy balance, and tended to have a lower metabolic respiratory quotient. Further, high-Meff cows had lower residual MEI, less heat energy loss, and lower plasma glucose concentrations, but used a greater portion of body reserves instead of feed energy for milk synthesis, particularly at wk 5 and 13 pp. However, these group differences did not persist by wk 42 pp. Cow groups were not different in O2 consumption, milk yield, metabolizable energy for maintenance, or the efficiency of tissue utilization for milk synthesis, but high-Meff cows tended to have the lower German relative breeding value functional herd life, indicating a link between metabolic performance and productive lifespan. In conclusion, the use of a clustering approach involving MEI/mBW, O2/mBW, and CO2/mBW seems to be a promising method to differentiate cows with divergent metabolic efficiency but does not allow identifying an individual metabotype that persists across the whole lactation cycle.
Keywords: dairy cow; energy metabolism; lactation; metabolic efficiency.
The Authors. Published by FASS Inc. and Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).