One of the most helpful, non-antibiotic additives developed for preweaned calves in the past several decades is mannan oligosaccharides, or MOS.

MOS is created by separating the cell wall from the yeast Saccharomyces cerevisiae. It is classified as a “prebiotic,” because it is a non-digestible food ingredient that influences the digestive bacterial population. MOS encourages the growth of beneficial bacteria in the gut microbiota by tying up harmful organisms.

When MOS is fed to preweaned calves, it mimics the intestinal attachment sites for the pathogenic bacteria that are the most common causes of scours: E. coli and Salmonella. When these bacteria bind to MOS, they are inactivated and excreted via the feces. In other words, MOS helps occupy and remove the “bad” bacteria from the calf’s gut, leaving more room for growth of the “good” bacteria.

In an analysis of 23 studies examining the impact of feeding MOS to preweaned calves, nearly all (21) of those studies reported an increased daily weight gain in calves that were fed the additive compared to a control group that was not.  On average, calves across all of the studies had a higher average daily gain (ADG) of about .15 pounds, and weighed 8.3 pounds per head more on average upon weaning at 2 months.

There are several high-quality MOS products available commercially, and we have the ability to blend virtually any of them into calf milk replacers at Strauss Feeds. Inclusion rate depends on the manufacturer’s and your nutritionist’s recommendations. Because MOS is a natural product, it has no required withdrawal time, and can be fed safely from birth to weaning. It works the same in every calf, and bacteria do not develop resistance to it like we have seen with some antibiotics.

It’s also much easier to prevent illness from occurring at all, than to deal with the production losses, increased labor, and drug costs incurred from clinical scours. Feeding MOS is a proactive, drug-free way to prevent disease and keep calves thriving, versus treating with antibiotics and enduring the setbacks that scours cases can cause.

In addition, MOS is highly affordable. Depending on the product and feeding rate, MOS costs about 1-3 cents per calf per day. So, for just $.50 to $1.50 per weaned calf, MOS can support intestinal health, maximize nutrition, and help calves develop strong immune systems that will support them throughout life. I’ve seen farms struggling with challenging scours situations that were partially solved with MOS. In more than one case, it produced a significant reduction in the occurrence and duration of scours in calves.

That being said, it’s also not a miracle substance. MOS works most effectively in calves that are raised with careful attention to nutrition, sanitation, and housing environment. I like to view feeding MOS as an insurance policy. When you need it, it’s extremely helpful, and when you don’t it’s there as a back-up, and won’t hurt anything. More than half of my clients currently include MOS in their milk replacer formulations, and some say they wouldn’t raise calves without it.