MANIPULATION OF RUMEN FERMENTATION: AN IMPORTANT STRATEGY TO IMPROVE LIVESTOCK PRODUCTIVITY

Rumen is well recognized as an essential fermentation vat that is capable of preparing end-products particularly volatile fatty acids and microbial proteins as major energy and protein for the host animal. The more efficient the rumen is, the better the fermentation end-products being synthesized. In the tropics, most ruminants have been fed on low quality roughages, agricultural crop-residues, and industrial by-products which basically contained high levels of lingo cellulosic materials, a low level of fermentable carbohydrate and a low level of good-quality protein. In addition, long dry seasons, a prevailing harsh environment, especially high temperature, low soil fertility and less feed available throughout the year, all influence Rumen Fermentation.

Alteration in ruminal microflora for improvement in growth and productivity can be achieved by means of additives that selectively affect rumen population. Please keep in mind that changes in one component of the rumen have several consequential effects on the other components. Microbial activity in the rumen is negatively altered by feeding large amounts of certain feed constituents (fats, starch) or minerals (buffer substances) which results in impaired anaerobic fermentation of forages and microbial protein synthesis. Modification of the rumen microbial population is now considered as a possible approach to rumen manipulation.

Ruminal microbes play a great role in the digestion of ligno-cellulosic feed. Anaerobic fermentation in the rumen converts components of the feed into useful (VFA and microbial protein) and unwanted (methane and carbon dioxide) end products. In tropics, low-quality roughages, crop-residues etc. containing high level of ligno-celluloses, poor in fermentable carbohydrate and good quality protein are given for ruminants. Strategies aiming to optimize rumen manipulation is key to improve feedstuffs utilization and then to optimize ruminant production. Manipulating ruminal fermentation involves maximizing the efficiency of feed utilization and increasing ruminant productivity (milk, meat, and wool production). It is intended to enhance beneficial processes, and delete, minimize, alter, processes that are harmful to the host.

WHY WE NEED RUMEN MANIPULATION?

Anaerobic fermentation of feeds in the rumen is beneficial for the host animal. The co-existence of animal and its microbial eco-system has resulted in stable and the most favored natural selection of microbes to perform the fermentation process optimally. Therefore, do we really need the manipulation of the rumen ecosystem? The answer to this question is definitely yes. During last three decades high producing varieties of plant and livestock have been evolved world over by genetic manipulation using scientific selection and breeding and also by application of biotechnological tools. Likewise, there exist considerable scope for selection and improvement of rumen microbial strains for improved feed utilization, better feed conversion efficiency and production performance of the animals. The rumen microbial ecosystem is not so efficient for digestion of ingested feed as evident from the presence of sizable portion of undigested feeds in the faeces and production of large amount of methane gas in the rumen which could be otherwise utilized as source of energy by the animals. Tropical/developing countries are poorest in the world on economic ground whereas richest area in terms of vegetation content. These countries import large quantity of plant protein to meet out the requirement/demand of growing human population. Ruminant animals act as important source of animal protein in the region. Ruminants of the region are mainly maintained/fed on poor quality roughage or lignocellulosic agroindustrial by products with or without concentrate supplementation resulting in poor productivity of the animals. Additionally tropical forages have some important limitation for animals feeding like: 1. Tropical forges have low energy value because their cell walls contain higher amount of lignin, silica and cutin resulting in lower fermentation of structural carbohydrate (Dominguez Bello and Escobar, 1997). Tropical forages in comparison to temperate produces less amount of VFA and microbial biomass (microbial protein) after ruminal fermentation, 2. Intake of tropical forages by the animals is low due to their poor ruminal digestion and prolonged retention time (Dominguez Bello and Escboar, 1997), 3. They are deficient of essential nutrients: contain lower amount of energy, protein (Egan et al., 1986) and minerals (Minson, 1980), 4. Feeding of tropical forages to the animals results in imbalance in digestive end products (high acetate and low propionate) which causes inefficient utilization of metabolizable energy (MacRae and Lobley, 1982), 5. Many plant species, particularly legumes and tree leaves contain anti nutritional compound (Jansen, 1975).

Therefore, considerable scope exist for manipulation of ruminal fermentation to improve the utilization of forages particularly in tropical as well as developing countries to maximize the productivity of animals by using available resources. Manipulation of rumen fermentation can be considered as an optimization process, whereby optimal condition are sought by maximization and/or minimization of fermentation process, depending on factors such as kind and level of feeding and animal production.

 Some of the major objectives of rumen manipulation are:

• Enhance fibrolytic activity: To increase the fibre degradation mainly through manipulation of lignocellulosic bonds in high lignocellulosic feeds as the rumen microbes are the only degraders of cellulose and hemicellulose, b. Increase microbial protein synthesis: A major portion of the amino acid reaching the duodenum are of microbial protein origin. Therefore, attempts should be made to maximize microbial protein synthesis in the rumen, c. Reduction in proteolysis: Hydrolysis of feed protein, deamination of amino acids and reutilization of ammonia for microbial protein synthesis are all energy consuming process, hence the degradation of protein and deamination of aminoacids in the rumen should be discouraged, d. Reduction in methanogenesis: Methane generation in the rumen is a wasteful process as 5-10% of GE intake of ruminants is converted in to methane. The provision of an alternate hydrogen sink in the rumen may help in increasing digestible energy (DE) availability for production, e. Prevention of acidosis: In high grain fed animals, the level of lactic acid can be controlled to avoid acidosis and inhibition of feed utilization due to lowered pH of the rumen liquor, f. Shifting acetate to propionate production: In fattening beef/lambs the production of propionate in the rumen at the expense of acetate may be helpful, g. Novel microbes: The quality of protein is important in high producing ruminants. Microbes, can be tailored to synthesize the amino acids in the form of the peptides and supply to the animals in the intestine, h. Metabolism of plant toxins: Rumen fermentation can be manipulated for efficient utilization of feeds which contain anti nutritional factors viz. tannin, saponin, mimosine etc, i. Synthesis of useful secondary metabolites.

 

MAJOR BENIFITS OF RUMEN MANIPULATION

• Enhance fibrolytic activity– Helps in manipulation of lignocellulosic bonds
• Increase microbial protein synthesis
• Reduction in proteolysis- Reduction in degradation of protein and decrease in deamination of amino acids
• Reduction in methanogenesis- The provision of an alternate hydrogen sink
• Prevention of acidosis
• Shifting acetate to propionate production
• Novel microbes
• Metabolism of plant toxins
• Synthesis of useful secondary metabolites

METHODS OF RUMEN MANIPULATION

• Genetic manipulation
• Non-genetic manipulation (Dietary manipulations)

A- GENETIC MANIPULATION

In genetic manipulation, attempts were made to develop genetically engineered rumen microbes by gene transfer/manipulation technique to enhance the animal productivity The potential of application of molecular techniques in achieving the goals of rumen manipulation are enormous.

OBJECTIVES OF GENETIC MANIPULATION

• To modify the distribution of fermentation products produced within the rumen to improve fermentation
• To produce metabolites (e.g., hormones) than can improve the metabolic efficiency of the animal
• To introduce improved or novel pathways for  degradation of feedstuffs
• To suppress the growth and metabolic activities of undesirable organisms

APPROACHES OF GENETIC MANIPULATION

• Introduce new species or strains of micro-organisms into the gut
• Genetic modification of micro-organisms already present in the rumen
• Common shuttle vector used- Escherichia coli
• Genes which have been cloned in Escherichia coli are endoglucanase, xylanase, β-glucosidase, amylase, glutamine synthetase
• Donor source of Bacteroides fibrisolvens, Ruminococcus flavefaciens, Fibrobacter succinogenes, Neocallimastix frontalis, Streptococcus bovis 

B- NON-GENETIC RUMEN MANIPULATION

1. FEED ADDITIVES
2. DEFAUNATION
3. PLANT EXTRACTS
4. FEED ADDITIVES

Feed additives are compounds added to the diet in order to improve dietary nutrient utilization, enhance performance, minimize the risk of metabolic diseases, and curtail adverse impacts of diets on the environment.

Feed additives classified into:

Ⅰ. MICROBIAL FEED ADDITIVES (PROBIOTICS)

Ⅱ. NON-MICROBIAL FEED ADDITIVES

CHARACTERISTICS OF FEED ADDITIVES

• Modulate ruminal pH and reduce lactate accumulation
• Reduce the risk of development of diarrhea in neonates and ruminal acidosis or bloat in older livestock
• Improve the efficiency of ruminal energy utilization
• Enhance rumen development in neonatal ruminants
• Increase ruminal organic matter & fiber digestibility
• Increase the level and efficiency of animal performance
• Improve the efficiency of ruminal nitrogen utilization
• Be cost effective and approved by legislative authorities
• PROBIOTICS

A live microbial feed supplement, which beneficially affects the host animals by improving its intestinal microbial balance. These are Direct fed microbes (DFM)

FDA defines DFM as a source of live naturally occurring microorganisms and this includes bacteria and fungi/yeast

• IONOPHORES

Ionophores are organic compounds mainly from Streptomyces spp. that facilitate selective transportation of ions across the outer cell membrane.

E.g. Monensin (widely used ionophore as `Rumensin’), Lasalocid, Tetronasin, Nigericin, Salinomycin, Lysocellin, Narasin, Laidlomycin and Valynomycin

Ionophores are approved in several countries including Australia, Argentina, New Zealand, and South Africa and USA

EFFECT OF IONOPHORES ON RUMEN END PRODUCTS

Ionophores favor propionate production. The associated decrease in production of methane that conserves energy in the ruminants. Ionophores inhibit gram-positive bacteria. They cause decrease in hydrogen and formate, a precursor of methane.

ORGANIC ACIDS

Commonly used organic acids are Fumarate, Malate and Aspartate. They stimulate propionate production in the rumen by acting as an H₂ sink, thereby reducing the amount of CH₄.

ESSENTIAL OILS

Essential oils are plant secondary metabolites, volatile components and aromatic lipophilic compounds with very strong antimicrobial properties, which inhibit the growth and survival of most microorganisms in rumen. They help to modulate cellular targets particularly by interacting with processes associated with the cell membrane such as ion gradients, protein translocation, phosphorylation, ATP production. Like monensin, selectively inhibit gram-positive bacteria as like monensin.

• EXOGENOUS FIBROLYTIC ENZYMES

Commercial mixtures of cellulase and hemicellulase enzymes with varying endoglucanase, exoglucanase, xylanase, protease, β-glucosidase activities have shown promise at hydrolyzing plant cell walls. Enzymes can improve fibre digestibility and animal productivity. Further, lower the acetate: propionate ratio in the rumen and ultimately reducing CH₄ production.

• FAT SUPPLEMENTATION

Fat supplementation increases the dietary energy content. Among fatty acids, the medium-chain C8:C14 from coconut or palm oil is the most effective in CH₄ mitigation.  Furthermore, fats are not metabolized in the rumen and therefore do not contribute to methanogenesis.

• DEFAUNATION

The process of making the rumen of animals free of rumen protozoa is called defaunation and the animal is called defaunated animal. Rumen protozoa elimination by defaunation reduces the ruminal methane production and increases protein outflow in the intestine, resulting in improved growth and feed conversion efficiency of the animals. Defaunation increases the number of amylolytic bacteria.

METHODS OF DEFAUNATION

Ⅰ. Isolation of newborn animals:

• Separation of newborn animals from their dams after birth and preventing them from any contact with the adult ruminant animals.
• The newborn animals should  be separated 2 to 3 days after birth.

Ⅱ. Chemical treatment

• Copper sulphate
• Manoxol
• Sodium lauryl sulphate

Ⅲ. DIETARY MANIPULATION

Offering high-energy feed (especially cereal grains like barley, maize) to the starved (for 24 hours) animals creates acidic condition in the rumen and rumen pH fall below 5.0. Ciliate protozoa are very much sensitive to rumen pH below 5.0. This fall in rumen pH eliminates the ciliate protozoa and the animal become defaunated.

• PLANT EXTRACTS                           

The antimicrobial activity of plant extracts – Secondary plant metabolites (saponins, tannins, Anthraquinone andSinigrin) is prominent. Plants exhibiting anti-methanogenic activity include Equisetum arvense, Lotus corniculatus, Rheum palmatum, Salvia officinalis, Sapindus saponaria, Uncaria gambir and Yucca schidigera. Major commercial source of saponins- Yucca schidiger

CONDENSED TANNINS

Development of forages with higher levels of tannins, such as clover and other legumes, including trefoil, vetch, Sulla and chicory promotes CH₄ mitigation (upto 55%). Condensed tannins can bind protein by hydrogen bonding at near neutral pH (pH 6.0 to 7.0) in the rumen to form CT-protein complexes, and then dissociate and release bound protein at pH less than 3.5 as they enter the abomasum and small intestine. VFA production increases and there is shift from acetate to propionate production.

Feeds supplemented with tannins or tannin rich forages, which bind proteases and thus prevent proteolysis. Methanol extract of Harad (Terminalia chebula) containing tannin decreased methane production in vitro by 95% when given at the level of 0.25ml/30ml. But the Limitations Is it Impede forage digestibility and animal productivity when fed at a higher concentration.

SAPONINS

Saponins are naturally occurring surface-active glycosides that are found in a wide variety of cultivated and wild plant species. They are antiprotozoal at lower concentrations. At higher concentrations can suppress Methanogens.

CONCLUSIONS

• Rumen should be manipulated essentially by altering the composition of rumen microflora, feeding local plants or tree leaves to defaunate the animals for improving its productivity.
• Genetic manipulation of rumen microorganism for efficient ruminal fermentative digestion has an enormous biotechnological potential.
• However in India, more emphasis should be given for manipulating the rumen to increase cellulolytic activity for efficient utilization of low grade roughage.

DR B SAINI, NDRI