Exogenous enzymes are widely used with the basic objectives of:
increase the capacity to utilize the nutrients available in raw materials
eliminate the antinutritional factors
Currently, phytases and carbohydrases are being used in virtually all monogastric diets under intensive farming conditions.
The investigation of the enzymes
1876. The history of enzyme investigation is closely linked with the history of biochemistry. The term “enzyme” (in Greek levadura ) was used for the first time in 1876 and it is attributed to the German physiologist Wilhelm Fiedrich Kühne.
1860. Louis Pasteur concluded from his experiments that the fermentation is catalyzed by enzymes.
1926. The first enzyme ( Urease ) is crystallized from the jack bean Canavalia ensiformis.
1930. The prolific author who published a theory on the origin of life together with Oparin, John Burdon Sanderson Haldane, wrote in his treatise “Enzymes”: “The weak-bonding interactions between an enzyme and its substrate might be used to catalyze a reaction”.
This idea is the center of our current knowledge on enzymes mode of action.
Use of enzymes in ruminant diets
In the case of using enzymes in ruminant diets , in 1960 Wise Burroughs’ team, from Iowa State University, published a paper on the use of combined enzymes (Agro-Zyme from MSD – Merck, Sharp & Dohme) in fattening cattle diets.
Since this first publication on the use of enzymes in ruminant diets, some results have attracted attention:
The increases in average gain and feed conversion are not associated with improved digestibility of dry matter, organic matter, protein or cellulose in enzyme-supplemented diets.
Subsequent studies have demonstrated that the supplementation with cellulases or xylanases (fibrolytic enzymes) can improve ruminal digestibility, that is, change the nutrient digestion sites and, consequently, improve energy efficiency.
Some of the reasons that justify the use of enzymes in ruminant diets are:
1) The organic matter digestibility in ruminants rarely exceeds 90%;
2) There is a growing utilization of agro industrial by-products , typically of low quality;
3) The faster carbohydrate availability , which normally stimulates the growth of microbial populations;
4) the presence of polysaccharides of different sizes that can have a prebiotic effect;
5) the use of exogenous enzymes can cause effects which are multifactorial in origin – in summary, the assumption is that the enzyme improves nutrient utilization , or changes the site where bonds are broken, and nutrients are released to the animal.
At the first glance and in a simplistic way, it seems clear that enzymes should be used in ruminant diets to increase the utilization of fibrous parts and also rumen utilization (Figure 1).
In an interview given to a Galician media, the Director of Agriculture and Natural Resources of the University of South Dakota (USA) Alvaro García stated:
“The digestibility of forage fiber determines the profitability of livestock production”.
To do this, there are several alternatives:
1) selection of grains and forages with higher nutritional value
2) improve the degradation capacity of rumen microbiota
3) use of additives that can change rumen fermentation standards
4) development of more efficient feeding practices
5) use of non-conventional raw materials
6) use of chemical or biological treatment in forage
7) use of exogenous enzymes to increase the digestibility of cell walls and/or starch (Rojo-Rubio et al., 2007)
The enzymes used in ruminant diets should have the same characteristics as all other enzymes in the market, such as:
adequate amounts of coenzymes
cofactors and activators to optimize their activity
composition that remains unchanged in all batches
thermostable during the manufacturing processes
completely safe
Also, they should have other characteristics improved:
digestibility of neutral detergent fiber (NDF)
be resistant to the degradation of rumen microorganisms
have a liquid form or dissolve rapidly and completely in water (as the rumen environment is liquid)
Once it is clear that the use of enzymes in ruminant diets can be economically attractive, it is time to define two things: what portion of the diet it is preferable for the enzymes to act on, and what part of the gastrointestinal tract must be affected by the enzymes….
Fibrolytic enzymes
Since the first study in 1960, a fibrolytic enzyme acting on the rumen was used (Figure 2, Fiber degradation)
As there were no products developed specifically for ruminants, enzymes created for other industries (pulp and paper, textile, fuel and fine chemistry) started being used. However, the most common were the enzymes used to improve silage production.
Products with residual activity are also marketed and, in these cases, the commercial product contains the medium, metabolites and fermentation products.
The ligninolytic enzymes are obtained from wood basidiomycetes (fungi), which oxidize the phenolic as well as the non-phenolic compounds. The enzymes have been investigated in lambs, using increasing doses, and the results showed higher ingestion and higher digestibility (this latter had a quadratic effect on the diet that is difficult to explain).
In general, fibrolytic enzymes may increase:
dry matter and fiber digestibility
production of volatile fatty acids, reducing rumen pH and synthesis of microbial protein
rumen activity
However, they also:
Increase methane production
and, according to published data, no changes are observed in rumen acetate:butyrate ratio.
Alpha-amylases
The alpha-amylases are radical innovations for the nutrition of dairy cattle and particularly can be used to maximize starch use and fiber utilization (Figure 4).
These enzymes act on the rumen by improving starch hydrolysis and catalyzing the reaction that converts starch into oligosaccharides, without affecting the pH (Bach, 2011).
The oligosaccharides can be used as energy sources through the fibrolytic bacteria.
It is possible to reduce fiber digestion time when the fibrolytic microorganisms have more energy available.
It has been demonstrated that the enzymes almost double the rate of starch and fiber (NDF) rumen degradation and, consequently, a higher activity of organic matter is observed. It causes a general improvement in total feed digestibility (Figure 5).
The results indicate that the starch energy provides more energy to the cows, besides increasing forage digestion .
As a result, the cows make more efficient use of the total feed and, therefore, feeding costs, milk production yield, production efficiency and quality are optimized (Figure 6).
RESULTS
MEAN: 1.95 – stdD 1.43
Max. 4.4 – Min: -0.8
References available on request
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