Residual feed intake in peripartal dairy cows is associated with differences in milk fat yield, ruminal bacteria, biopolymer hydrolyzing enzymes, and circulating biomarkers of immunometabolism.

Residual feed intake (RFI) is a common measurement of feed efficiency in dairy cattle. It indicates the difference between actual and predicted DMI for maintenance and milk production after adjusting DMI for the level of milk production. It is a reliable feed efficiency trait because it is independent of body size and level of milk production. Furthermore, RFI is highly repeatable across diets and stage of lactation (mid- to late lactation). The most efficient cows consume less feed than expected to meet their requirements for maintenance and milk production, whereas the least efficient cows consume more than expected. The difference is expected to be reflected in the physiological and metabolic profile of cows and therefore blood biomarkers should probably be an important addition to RFI evaluations.

Studies evaluating RFI divergence between dairy cows have usually been performed during established lactation. Whether shortening the feeding period and increasing the number of cows would enhance the ability to detect physiological differences between the most efficient and  least efficient cows is largely unknown. Thus, the main objective of the study by the authors referenced was to evaluate the association between RFI divergence during the pre-calf period in Holstein dairy cows and key ruminal bacteria, ruminal biopolymer digestive enzymes, and blood immune-metabolic biomarkers.

In the study, the authors classified multi-lactation Holstein cows (n = 320) from five studies into most feed-efficient (M-eff) or least feed-efficient (L-eff) groups using performance data collected during the pre-calf period. Differences in profiles of plasma biomarkers of immune-metabolism, relative abundance of key ruminal bacteria, and activities of digestive enzymes in ruminal digesta between them were investigated. Individual data from cows with ad libitum access to a total mixed ration from day −28 to day +28 relative to calving were used. A linear regression model including dry matter intake (DMI), energy-corrected milk (ECM), changes in body weight (BW), and metabolic BW was used to classify cows based on RFI divergence into L-eff  and M-eff. Plasma collected from the coccygeal vessel at various times around calving was used for analyses of 30 biomarkers of immune-metabolism. Ruminal digesta collected via oesophageal tube was used for DNA extraction and assessment of relative abundance (%) of 17 major bacteria using real-time PCR, as well as activity of cellulase, amylase, xylanase and protease.

The M-eff cows consumed less DMI during the pre-calf period compared with L-eff cows. Despite greater overall BW for M-eff cows, especially in the pre-calf period (788 vs. 764 kg), no difference in body condition score was detected due to RFI or the interaction of RFI × time. Milk fat content (4.14 versus 3.75 ± 0.06%) and milk fat yield (1.75 versus 1.62 ± 0.04 kg) were greater in M-eff cows. Although cumulative ECM yield did not differ due to RFI (1,138 versus 1,091 ± 21 kg), an RFI × time interaction due to greater ECM yield was found in M-eff cows. Among the plasma biomarkers studied, the concentrations of non-esterified fatty acids, β-hydroxybutyrate, bilirubin, ceruloplasmin, haptoglobin, myeloperoxidase and reactive oxygen metabolites were overall greater, and glucose, para-oxonase and IL-6 were lower in M-eff compared with L-eff cows. Among the bacteria studied, the abundance of Ruminobacter amylophilus and Prevotella ruminicola were more than two-fold greater in M-eff cows. Furthermore, despite lower ruminal activity of amylase in M-eff cows in the pre-calf period, regardless of RFI, a marked linear increase after calving in amylase, cellulase and xylanase activities was observed. Protease activity did not differ due to RFI or RFI × time.

Conclusions: The results indicate that despite greater concentrations of biomarkers reflective of negative energy balance and inflammation, higher feed efficiency measured as RFI in pre-calving dairy cows, might be associated with shifts in ruminal bacteria and amylase enzyme activity and therefore can in part be attributed to the enrichment of key ruminal bacteria involved in feed digestion and lactate consumption. Further studies could help address such factors, including the roles of the liver and the mammary gland.