Ruminal Acidosis

Ruminal acidosis is a dietary condition resulting from various degrees of over-eating on starchy foods, such as cereals and concentrate rations. Therefore, it often occurs under intensive sheep finishing systems (Piercy and Kemp, 1990). The degree of ruminal acidosis can vary from cases of indigestion with a mild watery scour to cases of sudden death or a very severe and distressing illness resulting in death (Braun et al., 1992). In more severe cases, the outlook is often poor and it may lead to complications, such as pregnancy toxaemia.

Ruminal Acidosis is often caused by sudden changes of diet, such as the introduction of concentrates in late pregnancy, altering the composition of micro-organisms in the rumen . In North America ruminal acidosis is frequently seen in feedlot lambs and lactating or pregnant ewes that have experienced rapid changes in their ration (Wolf, 2007), but it is unlikely to be seen in extensive grass-fed systems. In Mediterranean countries concentrate-based diets lead to cases of sub-acute acidosis (Blanco et al., 2015)

The rumen becomes more acidic than it should because concentrate-based diets increase volatile fatty acids production in the rumen, increasing the fraction of propionate and lactate which lowers the rumen pH (Enemark, 2008). An acidic rumen leads to inflammation or rumenitis (Patra et al., 1993; Piercy and Kemp, 1990). This in turn causes diarrhoea, dehydration and sometimes death. The energy metabolism in the liver of the animal may also be altered due to a limited availability of carbohydrate substrate (Huber et al., 1984).

Clinical signs of mild sub-acute cases are diarrhoea, but with continued appetite. In more severe cases animals are depressed, they stop eating and are often found standing or lying with ears down and grinding their teeth, which is indicative of abdominal pain. Temperature is low, with rapid heart and respiratory rates and shallow breathing (Braun et al., 1992).

If animal health is threatened by a disease, as in the case of rumen acidosis, the risk of associated disorders increases for example, parakeratosis-rumenitis, liver abscesses, laminitis (Penner et al., 2011) and blood cell counts, especially leucocyte counts, and their response to stimuli (lipopolysaccharide (LPS), endotoxins) can be modified, thereby compromising the animal’s immune response (Penner et al., 2011).

Fresh, clean water should be provided at all times and changes in feeding must be introduced gradually to allow the rumen papillae to adapt. Home rations should be mixed thoroughly to prevent selection by the animals. Grains should be matured before inclusion and should preferably be fed in the whole grain form to sheep.

Tannins may be effective for slowing ruminal disappearance of barley to improve starch utilisation by ruminants (Martínez et al., 2005, 2006). The addition of live yeast may also be effective in reducing acidosis (Brossard et al., 2006). Sodium bicarbonate can also attenuate acidosis and lambs fed grain prefer foods and solutions containing sodium bicarbonate (Phy and Provenza, 1998a, 1998b).

Lower stocking densities and sufficient trough space should help to prevent bullying and ensure all sheep get a fair share of concentrate.