ISSUE FOCUS FEED & ADDITIVE MAGAZINE March 2022 47 • Shift in fungi population (decreasing the fungi population with high fibrinolytic enzymes, which are sensitive to low pH) • Rise in LPS rumen concentration (increasing the GNB strain and their lysis) • Influence on the third layer of Stratified Squamous Epithelium (SSE) (desmosomes and tight junctions) • Lower ruminal fiber degradation (reduction in the number of cellulolytic bacteria which are less resistant to acid pH) • Reduction of the total production of fatty acids (propionic, acetic, butyric), therefore less available energy • Lower rumen motility (also as a consequence of the smaller number of protozoa) • Shift the metabolites profile in rumen fluid (biogenic amines; ethanol and ethanolamine; N-nitrosodimethylamine) • The increased acid load damages the ruminal epithelium • Acid accumulation increases the osmotic pressure of the rumen, inducing a higher flux of water from the blood circulation into the rumen, causing swelling and rupture of rumen papilla as well as a greater hemoconcentration The last points are crucial, as this enables an easier passage of fluids from the blood to the pre-stomachs, greatly influencing the fermentation processes. Furthermore, with diets low in NDF, the level of chewing and salivation is certainly lower, with a consequent lower level of salivary buffers that enter the rumen and which would maintain an appropriate pH under normal conditions. RUMEN SUB-ACUTE AND ACUTE ACIDOSIS: A FERTILE GROUND FOR LPS Studies on SARA in dairy cows have shown that feeding high grain levels causes Gram- bacteria's death and cell lysis, resulting in a higher concentration of free LPS in the rumen. In a trial conducted by Ametaj et al. in 2010 (Figure 1), a lower ruminal pH and an increase in the concentration of LPS in the rumen fluid -measured as ng/ml (nanograms/ milliliter)-, was the result of increasing of NSC present in the diet (% of grains). In the rumen, the presence of Gram- is very significant, however the dietary changes towards high energy concentrates reduce the substates necessary for them to thrive, leading to their lysis and favoring gram-positive bacteria (Gram+). Gram+ also produce bacteriocins against a wide variety of bacteria, including many Gram-. Figure 2 shows the influence of ruminal pH in the population of different bacteria, many of which are crucial for the production of SCFA and, therefore, energy. It is therefore necessary to pay close attention to the energy level of the ration as an energy input (generally around 1500 – 1700 Kcal/kg of DM intake). At the same time, we need to ensure that the animal does receive and ingest that daily amount of DM. If ingestion is negatively influenced by acidosis (clinical or sub-clinical), this can lead to endotoxemia, with harmful consequences for the animal's health and production performance. Figure 1. The increase in the level of endotoxins in the rumen is directly correlated with an increase in ration concentrates Figure 2. Activity of main bacteria in the rumen in function of pH (Daniele Cevolani Edizioni Agricole di New Business Media srl 2020)
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