Cattle Sense: Fine Tuning Fermentation
10/29/2009 10:00AM
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Last month I wrote about the dynamic nature of rumen fermentation, and the fact that variations in specific microbial populations and diet components lead to differences in the actual yield of nutrients from that process. Armed with this knowledge, we can begin to consciously manipulate rumen function in ways that improve diet utilization and efficiency.
Specifically, there is potential value in practices or substances that accomplish one or more of the following:
Increase total production/concentration of volatile fatty acids (VFA);
- more energy available for maintenance and production
Increase the relative proportion of propionate, at the expense of acetate, in the VFA produced;
- utilized in more efficient metabolic pathways, increasing net available energy
Reduce methane production;
- reduced energy loss
Increase the flow of microbial cell protein leaving the rumen;
- more protein available for maintenance and production
Increased uptake and conversion of lactate to other end products;
- elevated rumen pH, which benefits fiber digesters and reduces acidosis risk
Eliminate protozoa from the rumen.
- improve nitrogen use efficiency by preventing bacterial N from being held up within protozoa that consumed the bacteria.
Dietary Factors
The amount and combination of specific feeds in the diet are key determinants of rumen microbial populations and activity. Nutritionists keep several basic principles in mind when designing diets that make the most of rumen fermentation.
1. Meet all the nutritional needs of desirable microbes, all the time. For cattle primarily consuming low-quality, slowly degraded forages, supplements that contain soluble nitrogen and sugar and(or) fiber can keep the “bugs” on a more constant balanced diet. Despite a considerable amount of research and discussion, the absolute value of nutrient synchrony -- having dietary energy, protein, and trace nutrients supplied at the same time -- is still not clearly understood. There is published work that supports this concept (as well as intuition). Free-choice supplements, which animals typically consume multiple times a day, is a practical way to spread intake more evenly over time.
2. Take advantage of positive associative effects. Our primarily opportunity is supplementing degradable protein with low- to moderate quality forages. Forage intake increased dramatically, and fiber digestion may also increase as well.
3. Avoid negative associative effects. This includes feeding moderate amounts of starch with a forage-based diet, and feeding relatively high levels (>5% dry matter intake) of fat. The presence of grain in the rumen encourages proliferation of starch-utilizing bacteria at the expense of fiber digesters (through competition for other nutrients, and concurrent drops in ruminal pH). Fat actually has anti-microbial properties, and above the 5% threshold will decrease fiber digestion.
Use of Feed Additives
There are a wide range of rumen-enhancing products available on the market, and this continues to be an exciting area of research. Some of the options available to cattlemen include:
Inonphores. This class of antibiotics has selective antimicrobial activity, inhibiting gram positive bacteria in the rumen. The resulting shift in populations changes the relative amount of specific VFA produced, increasing propionate relative to acetate, and reducing methane and lactate production. These products have also been shown to reduce amino acid deamination, which leads to more efficient nitrogen use. Monensin (trade name Rumensin®) is the only ionophore with a clearance for beef cows, although lasalocid (Bovatec®) and bambermycin (GainPro®) may be fed to replacement heifers. In growing cattle, it has been estimated that 200 mg daily can increase available energy at a level equivalent to one pound or more of corn.
Yeast and yeast extracts. These products have been shown to stimulate fiber digesting microbes, as well as lactate-utilizers. Some research also shows an overall improvement in digestibility, at least with high quality forages.
Fungal extracts. Their action may be similar to yeast-based additives, stimulating the fiber-digesters and stabilizing rumen pH.
Yucca extracts. These additives are positioned to lower ammonia concentrations and reduce methane production. They have anti-protozoal properties, and defaunation (removal of protozoa from the rumen microbial mix) is thought to improve N use efficiency. Yucca extracts may also inhibit some gram positive bacteria, and they contain components that bind to ammonia.
Dicarboxylic acids. Aspartate, fumarate, and especially malate stimulate lactate utilization in the rumen, moderating pH. In research based on high quality or concentrate diets, malate has been shown to increase total VFA production, decrease the acetate:propionate ratio, and reduce methane production. Responses are less clear with low quality diets.
Plant extracts. Sometimes referred to as “essential oils,” these compounds are the focus of much current research. These oily liquids are what give a plant its “essence” -- that is, fragrance and flavor. It is an accepted fact that many of these substances are biologically active, but we are just beginning to learn what effect they may have in the rumen. Initial research has been done on cinnamaldehyde (from cinnamon), eugenol (clove bud), capsicum (hot peppers), carvacrol (oregano, thyme), and extracts of juniper berry, eucalyptus, vanilla, garlic, anise, olive, coffee, and more. It appears effects are dependent on dosage, diet, and level of production. Some research has demonstrated impacts on specific rumen microbes, VFA production and composition, methane release, protein use efficiency, feedlot gains and efficiency, and dairy milk fat, protein and MUN. However, there are instances where the change was actually negative (e.g., reduced total VFA production, or decreased feed intake), or where there was no significant impact at all. And some work suggests animals/microbes may adapt to their presence in the diet. It is also important to realize that much of this early work has been done in the lab, and not in animals in production settings.
The take-home message is that we have a number of tools available to us to modify rumen function in a favorable manner. Decisions involving diet formulation or additive use, however, need to take into account the balance between a reasonable expectation for improved performance or feed savings vs. cost. Possible combinations of these technologies need to be evaluated relative to the likelihood of an additive effect -- if two products have the same mode of action, using both probably won’t double the response. There also has to be a practical method for delivering additives, which may be problematic on pasture. Including rumen modifiers in self-fed protein supplements may offer the best opportunity to capitalize on these tools and concepts.
Source: Dr. Cathy Bandyk