Starch-rich diets can cause subacute ruminal acidosis (SARA) in dairy cows with potentially different susceptibility according to lactation number. We wanted to evaluate the bacterial community and the fermentation end products in feces to study susceptibility to hindgut acidosis and dysbiosis. Sixteen dairy cows received a medium-concentrate diet (MC, 40% concentrate, 18.8% starch) for one week and a high-concentrate diet (HC, 60% concentrate, 27.7% starch, DM) for four weeks. Milk yield, dry-matter intake, chewing activity, ruminal pH, milk constituents, and fecal samples for short-chain fatty acids (SCFA), pH, and 16S rRNA-gene sequencing were investigated. The HC feeding caused a reduction in fecal pH, bacterial diversity and richness, an increase in total SCFA, and a separate phylogenetic clustering of MC and HC samples. Ruminal and fecal pH had fair correlation (r = 0.5). Cows in the second lactation (2ndL) had lower dry matter intake (DMI) than cows of third or fourth or more lactations (3rdL; ≥4 L), whereas DMI/kg body weight was lower for ≥4 L than for 2ndL and 3rdL cows. The mean ruminal pH was highest in ≥4 L, whereas the time spent below the SARA threshold was highest for 3rdL cows. The latter also had higher total SCFA in the feces. Our results suggest that hindgut dysbiosis is caused by increased substrate flow to the hindgut, but further investigations are needed to define hindgut acidosis. The 3rdL cows were most susceptible to rumen acidosis and hindgut dysbiosis due to high DMI level, but missing counter regulations, as suggested happening in 2ndL and ≥4 L cows.

Numerous studies have used the 16S rRNA gene target in an attempt to characterize the structure and composition of the epimural microbiota in cattle. However, comparisons between studies are challenging, as the results show large variations associated with experimental protocols and bioinformatics methodologies. Here, we present a meta-analysis of the rumen epimural microbiota from 11 publicly available amplicon studies to assess key technical and biological sources of variation between experiments. Using the QIIME2 pipeline, 332 rumen epithelial microbiota samples were analyzed to investigate community structure, composition, and functional potential. Despite having a significant impact on microbial abundance, country of origin, farm, hypervariable region, primer set, animal variability, and biopsy location did not obscure the identification of a core microbiota. The bacterial genera Campylobacter, Christensenellaceae R-7 group, Defluviitaleaceae UCG-011, Lachnospiraceae UCG-010, Ruminococcaceae NK4A214 group, Ruminococcaceae UCG-010, Ruminococcaceae UCG-014, Succiniclasticum, Desulfobulbus, and Comamonas spp. were found in nearly all epithelium samples (>90%). Predictive analysis (PICRUSt) was used to assess the potential functions of the epithelial microbiota. Regularized canonical correlation analysis identified several pathways associated with the biosynthesis of precursor metabolites in Campylobacter, Comamonas, Desulfobulbus, and Ruminococcaceae NK4A214, highlighting key metabolic functions of these microbes within the epithelium.

During early lactation, both primiparous (PP) and multiparous (MP) cows are commonly fed diets rich in starch and low in forages to support their high energy requirements. Yet, the PP cows experience this dietary challenge for the first time, which might result in higher odds for them to develop rumen and systemic health disorders. The primary objective of this study was to evaluate the effect of decreasing the amount of forages in the diet on chewing and sorting behaviors and rumen and systemic health variables in PP and MP dairy cows. Twenty-four lactating Simmental cows [8 PP, average dry matter intake (DMI) of 19.1 ± 1.1 kg/d; 16 MP, average DMI of 22.5 ± 1.1 kg/d] with a body weight of 737 ± 90 kg and 50 ± 22 days in milk were used in this study. Cows were first fed a total mixed ration with 60% forage and 40% concentrate [on a dry matter (DM) basis] considered marginal in forages for 2 wk. Then, cows were switched to a diet low in forages with 40% forage and 60% concentrate (on a DM basis) for 4 wk. Reticular pH was measured continuously with wireless pH-sensors inserted into the reticulum to calculate the subacute ruminal acidosis (SARA) index. Chewing activity was measured with noseband-sensor halters, and feed sorting was measured weekly. Blood samples were collected weekly and analyzed for metabolic and inflammation markers. Switching PP and MP cows from a marginal to low-forage diet decreased the time spent eating and ruminating per kilogram of DM. Primiparous cows chewed longer per kilogram of DMI than MP cows. Also, the PP cows sorted more pronounced for longer particles and against fine particles than MP cows did. Despite higher rumination activity per kilogram of DMI and the adaptive sorting behavior, the PP cows spent on average 4.6 h/d longer below a pH of 5.8 and had a higher SARA index (i.e., area pH <5.8/DMI) than MP cows, especially during the first week of the low-forage diet (9.5 vs. 4.8). The concentration of liver enzymes increased with the low-forage diet, which was especially pronounced in the PP cows. In conclusion, this study demonstrated greater susceptibility of PP cows to SARA and liver damage than MP cows fed the same diets. Although PP cows demonstrated greater chewing and ruminating activity per kilogram of DMI, as well as adapted sorting behavior in favor of large particles during the low-forage high-starch feeding, they developed more severe signs of SARA. This suggests higher forage fiber requirements for PP cows and the need for improved feeding strategies to mitigate rumen fermentation disorders during early lactation in these cows.

Dairy cows need sufficient physically effective fibre (peNDF) in their diet to induce chewing with the latter stimulating salivation and maintaining rumen health. Thus, monitoring of chewing activity can be a non-invasive tool to assess fibre adequacy, and thus helping in the optimization of the diet. The objective of this study was to investigate and compare chewing activities of cows during transition period and in the course of lactation. Simmental dairy cows, in four different production groups such as dry period (from 8 to 6 weeks ante-calving), calving (24 h before and after calving), early-lactation (7–60 days in milk), and mid-lactation (60–120 days in milk) were used in the study. Cows were fed partial mixed rations supplemented with different amounts of concentrates. The chewing and drinking activity were recorded using rumination-halters (RumiWatch System, Itin+Hoch GmbH, Liestal, Switzerland). Feed data analysis showed that the peNDF content of the partial mixed ration (PMR) was highest during dry period, decreased around parturition, reaching the nadir in the lactation, in all cases, however, exceeding the peNDF requirements. Chewing data analysis showed that rumination time decreased (p < 0.05) in the time around parturition (from 460 min/d during dry period to 363 min/d 24 h before calving) and increased again in early-lactation (505 min/d), reaching a maximum in mid-lactation (515 min/d). Eating time was lowest for cows during early-lactation (342 min/d) and the highest for those in mid-lactation (462 min/d). Moreover, early-lactation cows spent less time (p < 0.05) drinking (8 min/d) compared to other groups (e.g., 24 min/d the day before calving and 20 min/d postpartum). Monitoring of chewing activity might be a useful tool to assess rumen disorder risks and welfare of the cows during the transition period. It further shows promising results to be used as a tool to identify cows that are shortly before calving.

The main challenge in dairy cattle feeding is to find a balance between the energy and physically effective fibre (peNDF), required to maintain rumen health. In an attempt to regulate the balance between energy intake and rumen buffering, we hypothesized that the content of peNDF in the diet modifies eating and feed sorting patterns of the cows. Sixteen lactating Simmental cows were switched from a diet high in peNDF, with which they were fed for one week, to a diet moderate in peNDF for four weeks. Data showed that during the moderate peNDF feeding the cows increased sorting for medium-sized particles and avoided both long and very fine particles. In addition, cows decreased their eating time per meal, but increased the number of meals per day, obviously attempting to decrease the amount of fermentable substrate per time unit while maintaining high levels of nutrient/energy intake. Although these changes during the moderate peNDF feeding went along with a lower diurnal variation of ruminal pH, feeding of the latter diet did not prevent ruminal pH drop and increased the level of all liver enzymes, indicating liver tissue damage. In conclusion, the altered eating, chewing, and sorting behaviour of the cows during the moderate peNDF feeding could not alleviate the deficiency in peNDF, which resulted in ruminal pH depression and impairment of liver health variables.