Dr. Jim Quigley's latest "Calf Notes" helps producers evaluate the effects of SARA on the health of cows and calves.
In a terrific recent review of the effects of SARA on cow health, Plaizier et al. (2012) documented in great detail effects of grain-based challenges on cow health.
When cows (and, by extension, calves) eat lots of grain in a short period of time (or when they are challenged with large amounts of grain), there is typically a reduction in the pH of the rumen, which can result in sub-acute rumen acidosis, or SARA.
Research suggests that many, if not most, calves experience SARA at some point during the rumen development period. In most research, SARA is defined as a rumen pH <5.8. When pH falls to this level, fiber digestion is depressed and the cow (calf) may experience various metabolic disturbances such as an on-off-on cycle of feed intake, loose manure, and depressed performance, among other problems.
A key component of SARA on animal health is the production of lipopolysaccharide (LPS) that results from the death of gram-negative bacteria. Also called endotoxin, LPS is a signal to the body that a bacterial invasion has occurred, and the body responds by mobilizing the immune response to fight off this new infection.
As a result, there are several clear signs caused by LPS – fever, production of pro-inflammatory cytokines such at TNF-α, anorexia, and, in severe cases, toxic shock and death. Normally, LPS is produced in the rumen as a result of normal rumen bacterial cell growth and death. However, concentrations are generally low, and intestinal systems detoxify LPS that leaves the rumen.
For example, abomasal proteases, lysozyme and hydrochloric acid, contribute by killing or inhibiting bacteria. Low abomasal pH can also deactivate LPS (Ribeiro et al., 2010). Bertok (1998) also reported that bile acids cause degradation of LPS in the small intestine.