Subclinical ruminal acidosis (SARA) is caused by a buildup of undesirable acids in the dairy cows’ rumen that exceeds its natural buffering capacity. This condition often leads to an erratic or persistent acidic condition in the rumen, and if left uncorrected, eventually compromises otherwise good milk performance and general health of a milking herd.
We tend to think dairy cows suffering from SARA would be staggering around the barn. In reality, some producers might not even notice SARA hiding in their herd. Therefore, the key to reducing SARA’s adverse effects upon performance and health is to identify its subtle signs and close any loopholes in lactation diets that allow SARA to enter your herd in the first place.
One of the first indications SARA might be present is milk fat tests have been slipping slightly for weeks or even months. These levels might even rebound on occasion. Yet given enough time, milk fat percentages will drop to undesirable levels. This down-up-down milk fat pattern is more than likely caused by waves of unwanted lactic acid accumulation and downward spiralling acetate levels (building blocks of milk fat) in the rumen.
If we suspect SARA is behind butterfat depression, we might walk among the cows in the barn to look for more subtle signs of SARA. It’s a good idea to watch all milk cows resting in their stalls after their last trip to the feed bunk. About two-thirds of them should be actively regurgitating their last meal and thoughtlessly chewing away. Undisturbed, Holstein cows naturally spend up to 10 hours a day chewing their cud.
Healthy ruminating cows produce large volumes of saliva, which is rich in sodium bicarbonate, that buffers volatile fatty acids produced from feed carbohydrates and prevents the rumen from becoming dangerously acidic. It is estimated an individual cow can produce about 150 to 200 litres of saliva per day, which maintains a normal pH of 6.0 to 6.5 in a healthy rumen. It also preserves a constant propionate to acetate ratio for good milk and butterfat production in the udder. In most cases, content and comfortable cows demonstrate that SARA is most likely not a significant problem.
In contrast, invisible SARA dairy cows have diminished cud-chewing activity, which may cause some to suffer from life-threatening bloat. They are unable to belch out ruminal gases (eructation), because of a lack of rumen motility. Similarly, these dairy cows are forced to endure “off-feed, on-feed” cycles caused by a toxic buildup of rumen acids and periodic relief of inefficient rumen buffering.
Manure from SARA cows is also diarrhea-like, pasty, shiny (intestinal sloughing) and contains small bubbles, rather than normal manure consistency, which is a porridge-like patty. Some SARA cows going through the “off-feed on-feed” cycle can cause SARAtype manure to disappear and be temporarily replaced by normal looking manure. Unfortunately, SARA conditions return as rumen acid levels rise, which causes water to be reabsorbed back into the gut and shiny loose SARA manure begins once again.
EXPERIENCE AND RESEARCH
It’s been proven by years of experience and confirmed by substantial university and independent research, SARA is caused by inadequate effective forage fibre consumed and fermented by dairy cows. Either not enough effective forage fibre is fed in the diet, too much starch from grain is provided to the cows that upsets ruminal forage fermentation, or the cows are “sorting out” a balanced diet for its grain portion, while leaving behind the necessary effective fibre from the forages.
Although, there is no definite fibre requirement compared to other dairy nutrients such as energy and protein, a common suggestion by many dairy nutritionists is the lactation diet should have a minimum neutral detergent fibre (NDF) recommendation of 27 to 30 per cent and 75 to 80 per cent of that minimum, forage related. In addition, the ideal particle length of any diet should supply 10 to 15 per cent of the forage particles that exceed a length of four cm. Lastly, the amount and type of non-structural carbohydrates (i. e. grain starches) should be examined.
With the advent of more feed by-products being fed to dairy cows, some high NDF ingredients such as corn distillers’ grains, wheat shorts and soy-hulls (pea screenings) have been mistakenly viewed as forage extenders or substitutes. One should keep in mind the fibre found in these by-products is not as effective as NDF from forages (and long-stem forage fibre) for buffering acids and thus maintaining rumen functions and desired butterfat levels. Instead, these byproducts tend to be high energy feeds that make up only partial forage substitutes. The only noteworthy exception is feeding whole cottonseed (wrapped in a cellulose coat) to lactating dairy cows. Its “fibre” content is believed to be nearly 100 per cent effective compared to actual forage fibres.
Sometimes dietary forage fibre for one reason or another is simply not available, so many dairy producers have relied upon “non-fibre” solutions. For example; adding dietary buffer supplements such as common sodium bicarbonate at the rate of 0.25 to 0.50 per cent has been shown to be relatively effective in reversing acidotic rumen conditions caused by feeding high-grain, low-effective-fibre dairy diets or when cows tend to sort their ration.
Consequently, sodium bicarbonate seems to work best at a ruminal pH of 6.2, and often increases it by +0.1 to +0.2 pH points. These changes seem small but in many cases, can prevent pH from dropping below the SARA threshold of 6.0, when fibre digesting bacteria populations dramatically die off, which leads to incomplete or improper forage fermentation for good milk production and cow health.
Such non-fibre solutions are only temporary in reducing the effects of SARA in dairy cows on the milking line. They need a solid foundation of high quality forages with effective fibre to promote good rumen function that is very effective in the prevention of even the most hidden SARA. These forages should be palatable, digestible and encourage dry matter intake by the lactating cows. They should also compliment the other non-forage ingredients in the diet, so all essential nutrients can be turned into high volumes of milk with desirable milk composition and profits.
PeterVittiisanindependentlivestock nutritionistandconsultantbasedinWinnipeg. Toreachhimcall204-254-7497orbyemailat [email protected]