Monica L. O’Brien, DVM

You run the risk of finding Subacute Ruminal Acidosis (SARA) in your cattle when you feed a diet rich in starch in order to achieve higher milk production or growth.  It can be an enormous problem in many dairy herds and can slowly creep in and steal away your profitability.   When the pH of the rumen is low or acidic, this is what is called ruminal acidosis.  Cattle, as you know, are adapted for a mainly forage diet so when we push them with grain we start to change the environment in the rumen.  Ideally, the rumen will have a pH of at least 5.5 or higher.  Cattle on grain are going to have rumen pHs on the lower end of normal.  The trick is to get high enough production out of the cattle, whether milk or growth, without pushing the rumen pH too low.  SARA is an acidosis that is at a low enough level that we do not see signs the same day but there is a delayed onset from the original insult of low pH.

The low pH in the rumen causes the lining to erode or ulcerate, thus allowing bacteria to colonize.  This can then leak into the circulation of the cow which could lead to abcesses on the liver.  These bacteria can also colonize the heart valves, lung, kidneys or joints.  Laminitis and subsequent sole overgrowth, sole abcesses, and sole ulcers may also be associated with SARA.  These foot problems generally do not appear until weeks or months after the original bout of ruminal acidosis.

Causes of SARA can be grouped into three categories: excessive intake of rapidly fermentable carbohydrates, inadequate rumen buffering; and inadequate ruminal adaptation to a highly fermentable diet.  Excessive intake is the most obvious cause in the dairy cattle industry.  These can be errors in feed composition or feed delivery.  In component fed herds, during early lactation cows are often brought up on grain faster than their actual rise in dry matter intake.  These cows are not able to consume enough forage to compensate for the extra grain.

Physical form of the feed can be an important factor in SARA.  Grains that are finely ground, steam-flaked, extruded, and/or very wet will ferment more rapidly in the rumen then unprocessed or dry grains.  Starch from wheat or barley is more rapidly and completely fermented in the rumen than starch from corn.  Corn silage that is very wet, finely chopped, or kernel processed also poses a greater risk for SARA.

Inadequate buffering:  Saliva is a natural buffer for the cow.  The amount of physical fiber in the diet determines the extent of buffer production by the salivary glands.  Coarse, fibrous feeds contain more effective fiber and stimulate more saliva production during eating than do finely ground feeds.  Diets with less then 7% long particles put cows at risk for SARA.  Also, diets with excessively long forage particles can also increase risk.  This is because these long particles are unpalatable and can easily be sorted through by the cow to get to the finer particles.

Rations can be evaluated with a particle separator to help determine if there is a potential problem with SARA or if changes need to be made to the ration or the feeding management.  It is much simpler to prevent SARA then to try and solve the problem once you have a whole silo of feed that is making your cow’s rumen unhappy.  We are strongly encouraging our producers to check their silage through the use of a particle separator.  Here are several areas where the particle separator could be effectively used.

During the harvesting process to make sure the appropriate particle size is being accomplished to facilitate the fermentation and feeding out process:

·         Making sure that there is no particle size reduction during mixing - compare mechanical mixed rations to a hand mixed rations;

·         Mixing consistency and ration uniformity (you want your particle size to be equal from one end of the bunk to the other); and

·         Total mixed ration (or TMR) sorting.  Collect samples at feeding and then at defined intervals afterward to determine the extent of the sorting.

We now have a particle separator at Rose Hill, so if you feel that you are having any of these problems or want to use this tool as part of your routine check of your nutrition program please have a talk with one of your veterinarians and they, or Crystal, our LVT, will be happy to help.