In the last issue we began a discussion of feeding technologies in the beef industry. We began with the use of direct-fed microbial (bacteria) products and the impact they might have on production in beef cattle. In this issue we need to examine the use of one of the most commonly used products of this nature – yeast and yeast products. Yeast products may assist in digestion of forages. One of the most common strains is Saccharomyces
cerevisiae and is produced by fermenting selected liquid and cereal grain raw ingredients with the specified yeast strain. Numerous strains or varieties of yeast products exist and there is some difference in the actual manner in which the different yeasts function. We will examine these differences a bit as well.
Additionally, over the last few years several yeast companies have learned to extract other products from the yeast they produce. These are typically derivatives of the yeast cell walls – remember that yeasts are essentially plants – and these cell wall components have shown benefit in a number of feeding protocols. The components extracted are carbohydrates which are normally indigestible in the rumen. Carbohydrates that are indigestible by mammalian enzymes can influence the composition and metabolic activity of the intestinal microflora and are therefore of interest for the formulation of livestock feeds, pet foods and specialized veterinary diets. Mannanoligosaccharides (MOS) are sugar-like carbohydrates that are isolated from yeast cell walls. They are not hydrolyzed by digestive enzymes as are other sugars and soluble carbohydrates. Instead they are broken down by different lactobacilli and some bifidobacteria (both are types of bacteria found in the gut) and seem to be less fermentable by intestinal bacteria than are fructooligosaccharides, another type of carbohydrate. Feeding of these compounds has shown to have beneficial effects in improving animal health response, much of which may be related to the binding of toxins and pathogens that can be common in a variety of animal feeds. We'll discuss these in more detail shortly.
Yeast usage has found applications in many livestock feeding areas. Yeast cultures have been shown to positively affect animal performance and mineral consumption. Studies in Florida and California resulted in improved feed intake, production, and reduced rectal temperatures during summer heat stress in dairy. Other research trials have shown that yeast cultures have also increased rumen bacteria numbers and improved the digestion of feedstuffs in both beef and dairy animals. Both mineral consumption and absorption have been positively affected by the addition of yeast culture to free-choice mineral mixes. Finally one 1986 study showed improved weight gains in yeast culture fed cattle grazing fescue pasture. Much of the eastern and southern United States has endophyte-infected fescue pastures as the main source of forage protein and energy. While new lines of endophyte-free fescue exist, it is unlikely that there will be wide-spread replanting of fescue areas for quite some time. There is a renewed interest in year-round or extended grazing to reduce the feed cost of cow-calf production programs. In some areas this has increased the interest in grazing fescue which promotes the need for methods to reduce the effect of endophyte-infected fescue.
In a study by Boyles and co-workers at Ohio State University gestating heifers
appeared to gain slightly more weight if they had access to a free-choice mineral
supplement containing yeast than a control mineral (Table 1). There also appeared
to be slightly more body-weight gain for the yeast- supplemented heifers compared
to controls during early-spring grass growth
Finally, this study showed that yeast inclusion increased total mineral supplemental intake. Total supplemental mineral intake was 0.23 and 0.40 lb per day for the control and yeast-mineral, respectively. The yeast-mineral intake was 4.8 ounces per day, and the total yeast consumption per day was 1.2 ounces per day. The difference in total supplement intake between treatments was 0.19 ± 0.072 lb per day.
From a different perspective, use of yeast has been shown to have a positive influence on intake in newly received stocker and feedlot cattle. Yeast appears to be useful in reducing stress effects in these cattle and has been shown to be of benefit in getting fresh cattle started on feed somewhat faster.
In yet other studies yeast products have been shown to have positive effects on ruminal fermentation, resulting in improved efficiency in the production of beneficial rumen products. Some researchers believe that with additional research and development, these yeast products could replace some of the additives currently being fed to improve rumen efficiency such as the ionophores. This could be of significant benefit as our market continues to push for reduced use of therapeutic and sub-therapeutic compounds (i.e. ionophores), in food animal production
Mannanoligosaccharides are a low inclusion feed additive containing mannan-based oligosaccharides derived from the cell wall of yeast. These complex sugars are of interest nutritionally because only certain microbes can utilize them for energy. For example, lactobacilli and bifidobacteria can, but coliforms cannot. The goal of adding MOS to the diet is two-fold:
• To provide the lectin on enteric pathogens with a mannose residue to block gut adhesion sites. I.e. it prevents pathogenic organisms from adhering to the intestinal lining.
• To provide a general stimulation of the immune system as gluco-mannan serves to enhance cell-mediated immunity, and activate the complement cascade (immunity process). As noted Glucans provide for immunostimulation while the mannans are not only immunostimulatory, they also block pathogen colonization and are non-nutritive to pathogens.
Glucan, mannan, and chitin are the main components of yeast cell wall. Glucan makes up the matrix of the cell wall, while mannan sugars protrude from the surface. The cell wall contains about 30 percent each of mannan and glucan, with the mannan fraction influencing cell adhesion, and the glucan fraction recognized by the immune system. This being said, at this time, MOS is known to influence animals through:
1. The presence of mannose or Mannanoligosaccharides in the intestinal tract also aids competitive exclusion. Pathogens bind the gut epithelium when lectins on these microbes recognize mannose-bearing receptors on gut epithelial cells. As pathogens become bound, they are unable to multiply, leading to the theory that beneficial bacteria will then be able to competitively exclude them.
2. Providing nutrients that only certain microbes can use is one way of supporting competitive exclusion. Chandler and Newman (1994) found that a number of beneficial intestinal bacteria were able to utilize MOS; however, most of the enteric pathogens could not. They also noted that the predominant ruminant species were unable to grow on MOS, indicating that MOS is poorly degraded in the rumen.
3. The other area of oligosaccharide supplements is stimulation of immune response. Bacterial cell wall materials, both glucan and mannan, activate the complement system via the alternative pathway. It is generation of the reaction products of the complement that increases the effectiveness of phagocytic (killer) cells such as macrophages to both speed clearance of antigens, and promoted the inflammatory response.
In a nutshell, MOS acts to bind an assortment of undesirable compounds which may enter the digestive tract by some route. Up to this point we have discussed pathogens although a variety of toxins my also be bound. For instance, reducing the negative impact aflatoxin has on performance of livestock has been the subject of numerous research trials. Research indicates that the feeding of clays, such as sodium aluminosilicates and bentonites, can bind or adsorb some of the aflatoxin and prevent them from being absorbed from the animal's intestine. In addition, mannanoligosaccharides (MOS), which are derived from yeast cells, may be effective in reducing aflatoxin's toxic effects. In general, the clay materials have been shown to bind 25 to 80 percent of the aflatoxin found in feeds when added to the ration at 0.5 to 1.0 percent of the total ration dry matter. Additionally, research indicates MOS may bind up to 80 percent of aflatoxins when fed at 0.125 percent of the total ration dry matter. However, due to variability in the ability of these compounds to bind aflatoxins, producers should not rely on these additives alone to fully restore performance and health or eliminate appearance of aflatoxin in milk. Additionally, neither the clays nor MOS are approved as anti-aflatoxin feed additives in the U.S.
MOS products have also been shown to have some positive effect on endopyte as well as other compounds potentially harmful to the animal.
The use of yeast and yeast derivative products have been shown to have merit in a number of animal feeding situations, especially calves and growing cattle. Obviously research is still required to better grasp application and how cattle respond to these products fed in different situations.
Dr. Steve Blezinger is and nutritional and management consultant with an office in Sulphur Springs Texas. He can be reached at 667 CR 4711 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at firstname.lastname@example.org. Also, visit BLN's web page at www.blnconsult.com.