The rumen is a complex ecosystem. It is home to a vast array of anaerobic bacteria, ciliate protozoa, anaerobic fungi, and archaea. Nutrients consumed by the ruminant animal are digested here by microorganisms anaerobically. The main end products of microbial activity in the rumen include volatile fatty acids, and microbial biomass, which are used by the host as a source of energy and protein. However, the ruminal fermentation process is not completely efficient because it produces some final products such as methane gas and excess ammonia. Manipulating ruminal fermentation involves maximizing the efficiency of feed utilization and increasing ruminant productivity (milk, meat, and wool production). Manipulating ruminal fermentation is intended to enhance beneficial processes, and delete, minimize, alter, processes that are harmful to the host.
Objectives of rumen Manipulation
Some of the major objectives of rumen manipulation are:
Methods of Rumen Manipulation
Non-Genetic Rumen Manipulation
Non-genetic manipulation of the rumen can be done by physical methods (dietary manipulation) by using suitable organic and inorganic compounds (dietary modulation) and by microbial feed additives. The intention of this dietary manipulation and nutritional interventions aims at manipulating feeding strategy to promote stable ruminal fermentation.
Approaches of rumen manipulation:
In general, dietary interventions involves supplementation of certain modifiers of rumen environment which have potential to alter associated ruminal microbial activity, which includes–
- Methane mitigation– Methane (CH4) formed in the rumen and released to the atmosphere constitutes an energy inefficiency to ruminant production. Redirecting energy in CH4 to fermentation products with a nutritional value to the host animal could increase ruminant productivity and stimulate the adoption of CH4-suppressing strategies.
- Ionophore antibiotics– Ionophores are an important nutritional tool used to manipulate ruminal fermentation dynamics and improve the efficiency and performance of beef and dairy animals. Ionophores are carboxylic polyether antibiotics naturally produced by an occurring strain of Streptomyces spp. Ionophores modulate the ruminal environment by targeting and altering the metabolism of Gram-positive bacteria, resulting in an increased concentration of ruminal propionate and a reduced acetate concentration. Another pronounced effect of ionophores is the mitigation of ruminal proteolysis and the consequent reduction in ammonia synthesis.
- Buffering compounds– Buffers in dairy rations are compounds that neutralize excess acid within the animal’s digestive system. They supplement the cow’s natural buffers that occur in saliva and increase her ability to overcome the harmful effects of too much acid production. Excessive acids in the rumen in situations where natural buffering systems primarily salivary flow, may be inadequate due to metabolic disorders like lactic acidosis which necessitates the practical supplementation of NaHCO3, CaCO3, MgO, bentonite (aluminum silicate clay) and sodium sesquicarbonate. Feeding ruminal buffers will maximise the microbial growth and production will maintain the high milk yields, safeguard herd health and maximise profitability.
- Organic acids– The use of dicarboxylic acids aspartate, fumarate, and malate stimulate lactate utilization by the predominant ruminal bacterium, Selenomonas ruminantium. Malate stimulates lactate uptake by S. ruminantium more than does aspartate or fumarate, and it seems that malate and sodium are involved in stimulating lactate utilization by this bacterium. Based on the ability of S. ruminantium to grow on malate in the presence of extracellular hydrogen and produce succinate, malate may be acting as an electron sink for hydrogen in the succinate-propionate pathway used by S. ruminantium. Incorporation of DL-malate into soluble starch and cracked corn fermentations with mixed ruminal microorganisms changed final pH, CH4, and VFA to enhance lactate utilization and simultaneously diminish the risk of lactic acidosis.
- Phytobiotics– Phytogenic feed additives or herbal products that have varying impact on the body are used as animal feeds for improving fiber digestibility, bacterial population (proteolytic and cellulolytic bacteria) concentrations, and rumen VFA, especially through an enhanced C3 concentration and, consequently, reduced CH4 production. These phytobiotics are gaining popularity nowadays because of their high efficacy in rumen manipulation.
- Plant secondary metabolites– PSM such as tannins, saponins, essential oils, and flavonoids act either by affecting directly methanogenic archaea or indirectly by disrupting the membrane of rumen protozoa. Some secondary metabolites also increase molar proportions of propionic acid in the rumen, thus rechannelling H2 away from methanogenesis toward synthesis of propionic acid.
MODIFICATIONS CAUSED BY SUPPLIES OF CERTAIN FOOD CONSTITUENTS
- Minerals and vitamins and growth factors, – Even when the diet is balanced for energy and protein, deficiency of minerals, vitamins and growth factors can depress microbial growth, efficiency and yield. Therefore, supplementation of growth factors and limiting elements under these situations may have a positive impact on digestibility and intermediary metabolism in rumen.
- Microbial feed additives and enzymes– Numerous direct-fed microbials that are accessible today have been recognized for their positive effects on animal’s weight gain, rumen development, nutrient digestion, restoration of intestinal microflora and competitive exclusion of the opportunistic pathogens. Major groups of this type of additives include Lactobacilli, Bifidobacteria, Propionibacteria which can be fed in the form of prebiotic, probiotic or synbiotic. Several microbial formulations are now commercially accessible, and their use serves as better alternative of antibiotics and growth promoters in livestock production. Similarly application of highly active enzymes (i.e. endoglucanase, xylanase, esterases, etc.) from the rumen source for commercial applications will provide a new dimension in agro-industries.
DIRECT MODIFICATIONS OF THE MICROBIAL ECOSYSTEM
The presence or absence of rumen protozoa is correlated with ruminal fermentation characteristics and methane production. Removal of rumen protozoa (defaunation) increases the bacterial population density, the efficiency of bacterial protein synthesis and the rate of nitrogen flow to the duodenum, especially when the feed is deficient in protein relative to energy content. Though carbohydrate digestion of plant cell walls is reduced by defaunation, improving protein supply and livestock productivity together with a reduction in methane production may be more important.
Ruminant production, especially in the tropics and developing countries suffers a setback when compared with the temperate and developed countries, which is attributable to the kinds of available feed resources in the region of production. Grazing on low-quality forages, crop residues and agro-industrial by-products with very little or no concentrate diets, adversely affect the animals in exhibiting their full production potential. Considering this fact, there is an increasing interest in improving the digestibility of these feed resources. Probiotics have been reported to improve the digestion of fibre and make structural carbohydrates such as cellulose and hemicellulose more available as an energy source for the host animals. The administration of probiotics had an impact on growth performance, disease resistance, improving animal production and providing a cost-effective dietary supplement; microbial feed additives also benefit ruminant nutrition in terms of live weight gain and milk production of the animals.
Genetic Rumen Manipulation
Genetically modifying the naturally available microorganism in the rumen enhances their capacity of defined functions or to add new functions and introduction of diverse genes into gut microorganisms have been explored. The genetically modified microorganisms are either able to digest fibrous components and lignins of forage, or degrade toxins, synthesize essential amino acids, reduce ruminal methane production and tolerate acids. Introducing new species or strains of microorganisms into the gut, like the former approach has a great potential to increase digestibility of feedstuffs and to improve animal production.
A number of rumen manipulation options are available and currently in practice. No single option appears to provide a simple and enduring solution. Selection and breeding of low methane emitter animals, use of chemicals, ionophors, plant secondary metabolites or such application attributes transitory effects. Even though genetically manipulation of rumen microorganism for efficient ruminal fermentative digestion has an enormous biotechnological potential. Based on the above conclusion the following areas need future research endeavors: a. Screening of non-conventional animal feeds specially tree leaves for anti-protozoal activity; b. Standardization of defaunation method for its implication at farmer level; c. New species/ strains of microorganism should be screened to use as probiotics; and mechanism of action of probiotic should be studied thoroughly.
Gurpreet Singh, Chetna Mahajan and Pallavi Khajuria
Department of Veterinary Physiology and Biochemistry College of Veterinary Science, Rampura Phul Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana