Acidosis is a common phenomenon encountered in the feedlot environment or when ruminants receive total mixed rations (TMRs). Generally caused by a grain overload, that causes a drop in the ruminal pH below 5.5, where an optimal pH of 5.8 is desired for high -grain feedlot rations, accommodating both fiber digesting and starch digesting microbes. In addition, sorting behaviour, changes in weather patterns, such as rainy weather or heat spells that cause irregular feeding behaviour, are also contributing factors to the incidence of acidosis.
What is sometimes overlooked, are the dietary conditions that present as acidosis (or present as acidosis symptoms in the ruminant), which are not necessarily due to the above. They will be discussed below.
Dietary Fat
Dietary fat is an alternative source of energy that can be used by ruminants. Due to the risk starch poses in diets (i.e. acidosis), nutritionists opt for fat sources to reduce the risk of grain overload, but still in an attempt to increase the energy content of the ration. This works specifically well for animals, where dry matter intake is the limiting factor to energy intake (such as finisher cattle). Dietary fat, does however, not come without its own risks or limitations. Fats have the tendency to become rancid quickly (which negatively affect feed intake) but also pose the risk of coating fibre particles in the rumen. Fibre, already being a minor component in feedlot rations, plays a critical role in the rumination process (chewing the cud which produces saliva- a natural buffer) and is critical for ruminal health and digestion. Once fibre particles become coated with fat, microbes are unable to access the fibre, effectively further “reducing” its presence and effect in the feedlot ration or TMR. This the also causes “acidosis-like” symptoms, not because there is not sufficient levels of fibre in the ration, but because the fibre becomes unavailable due to coating by fat particles. A high fat energy source includes hominy chop, frequently included in the rations of feedlot cattle. Feedlot cattle have a greater ability to tolerate higher levels of fat (6-7% of the diet), whereas sheep have demonstrated to not be that tolerant (4-5% dietary fat.)
Dietary Sulphur
Sulphur, a macromineral, is required in the production of essential amino acids. The limiting amino acid to production in ruminants is usually methionine, a sulphur-containing amino acid. However, as the saying goes, too much of a good thing becomes a bad thing. Sulphur is antagonistic to selenium, a micromineral important for the antioxidant status of the producing ruminant. Not only does excess sulphur in water or feed cause antagonistic reactions, it’s overconsumption is of greater concern than its deficiency. Diets high in sulphur result in polioencephalomalacia (PEM), which are nervous-like symptoms in ruminants, similar to thiamin deficiency, which also occurs in ruminants experiencing acute acidosis.
Thiamine deficiency
Vitamin B1, otherwise know as thiamine, is critical in metabolism to prevent lactic acidosis. Under normal conditions, thiamine is produced by microbes within the rumen, however, may be disrupted in the presence of excess Sulphur (as mentioned above) or due to carbohydrate and nitrogen levels. Similarly, a thiamin deficiency presents as PEM, which includes a retracted head, weakness, muscular twitching, diarrhea, labored breathing and even death. Animals that receive high grain diets, are at risk of a Vitamin B1 deficiency due to the drop in ruminal pH which cause for unfavourable conditions for thiamin-producing micorbes to survive and is sometimes supplemented in energy dense rations.
Acidosis is a debilitating condition in ruminants that decreases animal production and is a concern for animal welfare. However, all factors need to be considered, before acidosis can be accepted as the causative agent.
