How to maximize microbial protein production by ruminants
Fermentation study offers opportunity to lessen the need for escape-protein supplements
A lot of emphasis is placed on escape protein and in establishing the escape protein values for various ingredients. But has the industry been overlooking the obvious solution? Generally, at least half of the metabolizable protein supplied to the cow for protein synthesis is from microbial protein, with the remainder of the requirement met with escape protein from ingredient sources.
Microbial protein and the lactating dairy cow
The beauty of microbial protein is its quality and well-balanced amino acids. According to older data, regardless of the diet fed, the amino acid composition of microbial protein is surprisingly consistent. (Clark et al., 1992) The intestinal digestibility of the true protein component is also consistent, averaging about 85 percent. (Hvelplund, 1985, Storm et al., 1983)
Table 1 demonstrates the amino acid composition of milk as compared to microbial protein as well as several ingredient protein residues, which were analyzed after 12 hours of incubation in the rumen. The table provides an ample indication that the amino acid profile of microbial protein is reasonably close to the profile of milk protein. This suggests that as more microbial protein becomes available, formulating to meet amino acid needs of the lactating dairy cow should become an easier task.
In order to ensure the availability of microbial protein, the nutrient requirements of the microbes need to be met. Most ration-balancing programs commonly used today solve for the energy, total nitrogen and preformed protein needs of rumen microbes. The rumen nitrogen (N) balance section of Figure 1 shows the preformed protein (peptides) and total N (peptides + ammonia) required amply met the needs of the microbes.
Feeding rumen microbes
Are we lacking nutrients that might be needed by rumen microbes? Rumen microbes have distinctly different nutrient needs from lactating dairy cow. A considerable number of fermentation metabolites have been demonstrated to increase microbial growth and yield.
Studies have shown that yeast, yeast cultures, enhanced yeast products and other fermentation byproducts increase live performance of dairy cows. Other outcomes from feeding such fermentation residues have been greater fiber digestion and lower ammonia levels.
The mode of action of fermentation byproducts has been the subject of speculation. One explanation is that they provide a plethora of nutrients used by the microbial population and enhance microbial growth. A recent meta-analysis demonstrated a 15 percent increase in microbial protein yield with fermentation byproducts. (Lean et al., 2005) .
Supporting microbial growth in feed formulations
Can this increase in microbial growth be taken into account during feed formulation? As a follow up to the meta-analysis just described, an experiment was conducted by The Atlantic Dairy and Forage Institute, a private Canadian dairy research facility, to determine if diets can be formulated to produce higher microbial yield with fermentation byproducts.
The study compared a marginal protein, lysine-deficient control diet, a diet containing added blood meal, a fermentation extract alone (FERMENTEN) and the fermentation extract at a half level with added rumen protected lysine (MEGAMINE-L). The amino acid composition of rumen microbes was used in place of the fermentation product. The requirements for all amino acids were met with the three test diets.
The study showed that the protein resulting from the fermentation extract provided superior results to added high-quality porcine blood meal, which is frequently used to provide high levels of escape amino acids. Milk yield (Figure 1) and milk/dry matter (Figure 2) were highest with the fermentation enhancer.
Enhanced rumen fermentation
The importance of the study’s results resides in the fact that the added microbial protein produced by the fermentation enhancer can be taken into account during formulation. This will allow nutritionists to formulate diets and take advantage of this aspect of enhanced rumen fermentation, rather than trying to guess how cows might respond to additives.
While these products may provide additional contributions, the improvements in protein formation can make a significant economic contribution and relax the need for escape protein supplements.