Most of us have at least a basic understanding of rumen acidosis. In addition, we have a good idea of how to prevent or treat rumen acidosis. However, apart from a decrease in rumen pH and sloppy manure, what other impacts has rumen acidosis on the animal and at what cost to the animal?

1. Total DM intake is a major determinant of ruminal pH. DM intake increase as days in milk increase, leading to an increased risk for low ruminal pH (Krause & Oetzel, 2006). 
2. In beef cattle, depressed DM intake becomes more evident if ruminal pH falls below 5.6 (Krause & Oetzel, 2006).  
3. Acute rumen acidosis can have a long-term adverse effect on VFA absorption in the rumen. For example, propionate absorption of sheep was decreased by more than 40%, and liquid passage rate dropped by more than 50% six months after acute rumen acidosis incident (Krehbiel et al., 1995).
4. Because absorption of VFA across the ruminal wall accounts for 65 to 75% of the total ME supply in ruminants, any reduction in VFA absorption may reduce ADG and feed efficiency (Krehbiel et al., 1995).
5. Rumen acidosis may increase NEFA levels in the blood, indicating the change of energy supply to the animal (Dong et al., 2013).
6. Rumen acidosis may increase plasma cortisol levels. This can lead to the inhibition of protein synthesis while increasing protein breakdown (Dong et al., 2013).
7. Pancreatic tissue damage has been reported in animals experiencing ruminal acidosis (Krehbiel et al., 1995).
8. Rumen acidosis may reduce rumen barrier function, resulting in rumen bacteria such as Fusobacterium necrophorum and Arcanobacterium pyogenes that may translocate via the portal blood to the liver, possibly causing liver abscesses (Plaizier et al., 2008).
9. Rumen acidosis can increase the breakdown of gram-negative bacteria. This may lead to increased free LPS levels in the rumen and can result in an increase of the permeability of the gut for LPS (Khafipour et al., 2009).
10. Free LPS can translocate into the bloodstream from the digestive tract under conditions of high permeability and/or after injury to the epithelial tissue. This can, trigger an immune response, releasing pro-inflammatory cytokines that recognize the circulating LPS (Dong et al., 2013).
11. A continuous presence of a low amount of LPS in plasma of SARA induced cows could result in metabolic endotoxemia that triggers low-grade inflammation. Metabolic endotoxemia can result in insulin resistance in the liver, hyperinsulinemia, higher blood glucose level, modification of the energy metabolism, and anorexia (Cani et al., 2007).
12. Activating the immune response due to an LPS challenge may increase the animal’s energy requirement. LPS challenge in dairy cows increased the glucose requirement by ± 1 kg glucose over 12 hours (Kvidera et al., 2017).

Rumen acidosis has effects on different sections of the animal’s anatomy and physiology. Therefore, it is essential to reduce the risk of acidosis, especially when high concentrate diets are fed in high quantities, to optimise the production performance of the animal.