Bovine laminitis, one of the most cost of lameness conditions, is an economic drain on producers. It is generally accepted that micro-circulation of blood disorder within the corium induced by microbiota metabolites, such as LPS, lactate, and histamine, is the main pathogenesis of laminitis. Thus, in the present study, we detected the characteristics of rumen microbiota and the concentration of LPS, lactic acid, and histamine in the serum from cows between control and laminitis. The results showed that the concentration of LPS and lactate in serum were increased in the laminitis cows compared to the control cows. In addition, the elevated abundance of bacteria, including Candidatus Saccharimonas, Saccharofermentans, Erysipelotrichaceae UCG-009, Erysipelotrichaceae UCG-008, Clostridium papyrosolvens, and Ruminococcaceae bacterium AE2021, that riches acid- enhancing metabolites could lower the pH of rumen fluid, which leads to the death of gram-negative bacteria and release of endotoxins in rumen. However, the small samples size limits to some extent the generalization of the findings made in this study.
LPS is a major component of the outer membrane of gram-negative bacteria. As the main vasoactive substance, LPS plays a key role in inflammatory reactions. When ruminal acidosis occurs, plenty of gram-negative bacteria are dead and LPS release. In the early stage of laminitis, inflammation is the main manifestation. LPS is absorbed into blood circulation through the ruminal wall, and then reaches the micro-circulation of the claw. The local LPS has inflammatory effects, such as the activation of cytokines and acute-phase protein release, thrombocytopenia, leukopenia followed by leukocytosis [23. Besides, recent evidence suggested that pathological changes in inflammation could be made by injection of LPS . In this study, the concentration of LPS significantly increased in the laminitis group compared with the healthy group.
Lactic acid, as vasoactive substances as LPS, are associated with laminitis . Both of them can present a risk to claw deterioration and the laminitis process, including vasoconstriction, dilation, edema and thrombosis, and to interfere with the migration and function of defense cells such as neutrophils. Previous studies reported the increase of histamine and lactic acid in bovine serum during laminitis [4, 5, 24]. Our experiments confirmed previous results and lactic acid in serum of bovine with laminitis went up.
There is an evidence that ruminal bacterial community play a crucial role in pathologic regulation of organism in developing disease . The role of microbial populations received widespread attention across several disciplines in recent years. Therefore, a number of cross-sectional studies suggested an association among microbiota, its metabolites and laminitis. The proportion of phylum Firmicutes and genera Streptococcus and Lactobacillus significantly grew, while the abundance of phyla Bacteroidetes and Fibrobacteres and genera Butyrivibrio and Ruminococcus dramatically declined during the period of laminitis . However, our results showed that there are no significantly difference rumen bacterial phyla between laminitis and control bovines, this may be due to the different diets of different experimental animals. Our study was to collect rumen fluid samples from healthy and laminitis cows with the same diet, whereas other studies have been conducted in animal models of laminitis induced by high carbohydrate feeding.
In the present study, we observed the significant differences in bacterial community between the two groups using NMDS. In brief, compared to healthy group, the genera Candidatus Saccharimonas, Saccharofermentans, Erysipelotrichaceae UCG-009, and Erysipelotrichaceae UCG-008 increased, most of which were associated with fermentable diets and lower ruminal pH [27–29]. With the reduction of pH, plenty of gram-negative bacteria died and released more LPS. At the species level, Clostridium papyrosolvens and Ruminococcaceae bacterium AE2021significantly increased. As Boonsaen P argued, Ruminococcaceae (e.g. Ruminococcus flavefaciens and Ruminococcus albus) could produce lactate . These results suggested alteration of ruminal bacterial community may be a factor inducing laminitis by influencing rumen metabolisms, such as the increase of LPS and lactate.