Rumen Fermentation

The distinctive feature of ruminant digestive system is the fermentative digestion of feed materials through microbes, which occurs in rumen and reticulum. Besides, the fermenta­tive digestion of feed can also be seen in pseudo-ruminants such as llamas, camels, and hippopotamus.

14.4.1 Rumen as Microbial Habitat

Rumen provides congenial environment for the growth and multiplication of microbes. The rumen maintains a constant temperature of 40 °C.The HCO₃ andHPO₄ buffers of saliva provide a constant pH of 6-7. The saliva secretion also provides aqueous environment, thereby supplying substrates for continuous microbial activity. The primary contractions of rumino-reticulum aids in proper mixing of ruminal contents and the secondary contractions cause eructation (Fig. 14.4).

Rumen microbes use the host ruminants’ feed stuff constituting cellulose, hemi-cellulose, pectin, soluble sugars, and starch to synthesize their energy for growth. Conse­quently, the fermentation produces acetic, butyric, propionic, and lactic acids along with gases such as H₂, CO₂, and methane.

Abomasum is analogous to monogastric stomach and causes the hydrolysis of protein of both dietary and microbial origin, which is later absorbed in small intestine. The HCl and gastrin secretion are stimulated by a rise in abomasal pH and short-chain fatty acid levels. Gastric secretion occurs both from fundic and pyloric glands with the former as a major secretory source. The secretion from fundus region contains pepsin and HCl with pH close to 1.0, while that from pyloric glands is slightly alkaline with slight peptic activity.

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Fig. 14.4 Primary and secondary contractions. [The primary contrac­tion occurs every 60 s and includes two contractions of the reticulum, which reaches the rumen. It leads to the ingesta flow from reticulum to cranial ruminal sac and later to ventral sac. The secondary contraction

causes eructation. It leads to the ingesta flow from the caudo-ventral blind sac to the dorsal blind sac followed by dorsal sac (causes eructa­tion) and ventral sac in sequence]

14.4.1.1 Rumen Bacteria

Among the diverse microorganisms of rumen, bacteria are the predominant microbes contributing to nitrogen and car­bohydrate metabolism through fermentation (Table 14.1).

The rumen content comprises as high as10¹¹ cells per gram of rumen content with more than 200 species. Although the total volume of small bacteria is same as ciliate protozoa, the metabolic activity of bacteria is far greater than protozoa, presumably because of the greater surface area.

Table 14.1 The types, examples, substrates, and fermentative end products of rumen bacterial species

The rumen bacteria and their activities are known to be influenced by several factors, revealing the possibility of their manipulation. These factors include, but not limited to, feed­ing regimen, diet changes, antibiotic usage, animal’s age and health, season, stress level, geographic location, photoperiod, and environment.

14.4.1.2 Rumen Protozoa

Ciliates are the most abundant protozoa representing two physiologically and morphologically different groups viz. entodinomorphs and holotrichs, whereas flagellates occupy the niche to a very limited extent (Fig. 14.5).

The anaerobic rumen ciliates aid in digestion of plant material and ranges from 4 ? 106 per mL to 6 ? 106 per mL. On the basis of their substrates, the rumen protozoa were classified as starch degraders, soluble sugar utilizers, and lignocellulose hydrolyzers. The large quantities of reserve starch stored in protozoan vacuoles could be used on exhaus­tion of exogenous energy supply. Larger protozoa prefer structural polymers while smaller protozoa ingest sugars and storage polymers. Generally, holotrichs use soluble sugars and entodinomorphs utilize starch and other plant materials. The protozoal count is affected by ruminal pH, composition of diet, digestibility of diet, frequency of feed­ing, and season. Protozoa contribute 19-28% of cellulase activity of the total rumen fibrolytic activity. Protozoa are also a good source of lipids and roughly 27% of total lipids are thought to be contributed by holotrichs.

14.4.1.3 Rumen Fungi

The ruminal anaerobic fungal inhabitants range from10⁵ to 10⁷ per gram and include Neocallimastix frontalis, Sphaeromonas communis, and Piromonas communis. Rumen fungi degrade unlignified components of plant cell walls by producing cellulases, hemi-cellulases, and particu­larly xylanases. High roughage diet increases the fungal proportion, consequently increasing the adhesion and degra­dation of plant cell wall. The uniqueness in fungi lies in their ability to penetrate the cuticle.

14.4.2 Fermentation OfCarbohydrates

The carbohydrate fermentation aids rumen microbial popula­tion to attain energy for growth and multiplication. About 75% of the plant tissue dry matter comprises carbohydrates. Microbial fermentation breaks carbohydrates into simple sugars. The end products of carbohydrate fermentation include volatile fatty acids (acetate, propionate, and butyrate) and gases (carbon dioxide and methane).

The speed of fermentation depends on the structure and solubility of carbohydrates. Glucose is a simple sugar with a molecular formula C₆Hi₂O₆. Starch contains amylose and amylopectin as polymer chains. Cellulose is beta 1,4 glucose linkage polysaccharide, and hemi-cellulose is composed of beta-linked xylose units and few hexoses. Pectin is beta­linked galacturonan (polysaccharide based on galactose with uronic acid). Lignin, a phenolic compound, is resistant even to microbial enzymatic digestion. Majority of the lignin is indigestible.

Fig. 14.5 Classification of rumen protozoa. [The Isotricha and Dasytricha genera belongs to Isotrichidae family while the genera Entodinium, Diplodinium, Epidinium, and Ophyroscolex belongs to Ophyroscolediae family]

The extent of carbohydrate fermentation and the end products depends on the type of diet, maturity status, ruminal pH, anti-nutritional factors, and type of microbes. Matured forages are less digestible due to the higher proportion of lignin. Similarly, young grasses are more digestible due to the lower lignin quantity and higher fructosans fraction. Feeding roughage-rich diets leads to the production of acetate at higher proportion and concentrate-rich diet produces higher amount of propionate as end product.

Degradation of carbohydrates involves four steps.

14.4.2.1 Adherence

The bacteria adherence process plays a crucial role in fiber digestion. In the first phase, bacteria transport to fibrous substrate. Later the initial nonspecific adhesion of bacteria to substrates is followed by the specific adhesion of bacteria with digestible tissue. Finally, the attached bacteria prolifer­ate to form colonies on specific sites of the plant tissue. Among various bacteria, coccoids prefer to attach plant cell wall. Attachment helps the bacteria to retain for a longer time and facilitates sustained action. Further, the adherence renders the produced enzymes to come into contact with the substrate and ensures that resulting degradation products are preferentially available. The adherence will be maximum at 40 °C, decreases at a pH below 5.0, and is facilitated at the pH of 5.5-7.8. Certain rumen fluid factors such as phenyl propanoic acid and phenylacetic acid stabilizes the bacterial adherence. The lignin and soluble cellulose derivatives like carboxy methyl cellulose are found to inhibit bacterial attachment.

14.4.2.2 Disaggregation

The fibrous feeds soak in the rumen fluid breaking them into small pieces. Disaggregation increases the degradable ability by rumen microbes. For instance, the starch granules are easily attacked on grounding.

14.4.2.2.1 Extracellular Degradation

The rumen liquor is the best source of bacterial and protozoal enzymes. The enzyme activities in rumen fluid are diverse. They include, cellulases, xylanases, β-glucanases, pectinases, amylases, proteases, phytases, and toxin-degrading enzymes such as tannases. Many of these microbial enzymes act on the soaked and disaggregated feed substances within the rumen, degrading them into short-chain oligosaccharides and sugars. Most of the crystalline cellulose is degraded through extra­cellular fungal cellulases.

14.4.2.2.2 Intracellular Degradation

The bacteria engulf simple sugars produced through the degradation of oligosaccharide and disaccharides. The intracellular enzymes of microbes metabolize mono- and disaccharides through phosphoroclastic cleavage forming pyruvate, phosphoenol pyruvate, volatile fatty acids, CO₂, and methane (CH₄). The bacterial enzymes degrade starch to maltose and glucose. Maltose is fermented to glucose, which gets converted to pyruvic acid through a metabolic pathway known as glycolysis. The anaerobic glycolysis yields two ATP molecules, contributing the energy source for rumen bacterial maintenance and growth. The degradation of amor­phous form of cellulose occurs in anaerobic cellulolytic bac­teria by producing enzymes such as endo-β-glucanohydrolase, glucosidase, and endo-xylanase. The hemi-cellulases are highly degradable compared to cel­lulose and require bacterial cellulases. The β-glucosidase hydrolyzes cellobiose and cellodextrins, producing hexose; however, the enzymatic degradation of hemi-cellulose yields pentoses. Pectin, a polymer of galacturonic acid, will be finally converted to short-chain fatty acids.

14.4.2.3 Formation of Volatile Fatty Acids

The pyruvate, an intermediate compound of carbohydrate fermentation, yields volatile fatty acids, CO₂ and CH₄. The metabolic pathways of pyruvate degradation are presented in Fig. 14.6. The yielded short-chain fatty acids act as major energy sources in ruminants.

14.4.2.3.1 Acetic acid formation

The acetic acid formation occurs in two pathways:

1. Oxidative decarboxylation of pyruvic acid

The pyruvic acid formed during glycolysis enters into mitochondrial matrix and gets converted to acetyl CoAby removal ofCO₂ and H₂, in the presence of thia­mine pyrophosphate (TPP) and lipomide. The reaction is catalyzed by pyruvic dehydrogenase. The Acetyl-CoA yields acetic acid by removal of thioester bond and coenzyme A.

2. Phophoroclastic split

The phosphoroclastic reaction of pyruvate cause the for­mation of acetic acid and formic acid from two molecules of pyruvic acid yield. Being the simplest carboxylic acid, the formic acid (H₂CO₂) is dehydrogenated to CO₂ and H₂. A portion of the generated H₂ is utilized for the production of succinate, propionate, butyrate, and lactate and biohydrogenation of unsaturated fatty acids. Remaining portion will be utilized by methanogenic bac­teria for methane production.

14.4.2.3.2 PropionicAcid Formation

The propionic acid formation occurs in two pathways:

1. By carbon dioxide fixation: The pyruvic acid combines with CO₂ forming oxalo-acetic acid, which is further

Fig. 14.6 Themetabolic pathways of pyruvate degradation. [The phosphoclastic split of pyruvate yields acetic acid consequently producing CH₄. The propionates act as H sink and competes with CH₄, thereby indirectly regulating the CH₄ production whereas the acetate and butyrate formation releases hydrogen]

reduced to malic acid. The resultant malic acid is converted to fumaric acid on removal of one water mole­cule. The hydrogenation of fumaric acid produces succinic acid followed by its decarboxylation yielding propionic acid.

2. By acrylate pathway: The pyruvic acid produces lactic acid on hydrogenation and the resultant lactic acid is converted to acrylic acid on removing water. The hydrogenation of acrylic acid yields propionic acid.

14.4.2.3.3 Butyric Acid Formation

The different pathways of butyric acid formation are two molecules of acetyl-CoA condense to yield acetoacetyl- CoA and 2H₂ by 3-ketoacyl-CoA thiolase. The acetyl-CoA is converted to beta hydroxybutyrl CoA by reduction. The resultant beta hydroxybutyrl CoA is converted to crotonyl CoA on removal of one H₂O molecule. Reduction of crotonyl CoA leads to formation of butyrl CoA along with one mole­cule of ATP. The butyrl CoA yields butyrate.

14.4.2.4 End Products OfCarbohydrate Fermentation

The end products of carbohydrate fermentation include short­chain fatty acids (acetate, propionate, and butyrate), isoacids (valeric, isovaleric, isobutyric, and 2-methylbutyric acids), and gases such as CO₂, CH₄, and H₂. The CO₂ accounts for 40% of the total rumen gas, CH₄ accounts nearly 30-40% and hydrogen about 5%. The extra hydrogen should be removed from the rumen to maintain pH and rumen ecosys­tem. Methane acts as hydrogen sink and is considered as net energy loss as most of the CH₄ is lost as eructation. On an average, 4.5 g CH₄ is produced for every 100 g carbohydrate digested.

The total volatile fatty acid content of ruminants ranges from 60 to 120 mEq/L. The individual concentrations of VFA depends upon substrate composition, rumen ecosystem, and health status. The volatile fatty acids proportion changes according to the diet fed. The ratio of acetate, propionate, and butyrate ranges from 70:20:10 for high forage diets to 60: 30:10 for high grain diets. The rumen liquor of ruminants fed with normal mixed diet contains 60-65% acetate, 15-20% propionate, and 10-15% butyrate.

14.4.2.5 Absorption of Volatile Fatty Acids

The VFA are directly absorbed from the rumen, reticulum, omasum, and large intestine. Undissociated acids absorb directly by simple diffusion in pH conditions of less than or equal to 6.7. The rate of absorption of VFA increases with the decreased pH, thereby regulating the rumen pH. The absorp­tion of VFA results in accumulation of CO2 and HCO3 ion concentration. Lactacidemia is observed because of the lac­tate absorption on feeding high starch diets. Increased lactic acid formation in the rumen. Increased lactic acid formation in the rumen reduces rumen pH, leading to lactic acidosis and increased Streptococcus bovis. Low pH suppresses the growth of other types of bacteria sensitive to pH-causing rumen dysfunction and dehydration. The spiral flow chart of the rumen acidosis sequel is provided in Fig. 14.7.

14.4.2.6 Utilization of VFA in Ruminants

The fermentation of fiber yields acetate as main end product. Low energy and high fiber diets such as roughage leads to

Fig. 14.7 Spiral flow chart of the rumen acidosis sequel. [Feeding rapidly fermentable carbohydrates lead to severe rumen acidosis and death of the animal]

increased ratio of acetate to propionate. Milk fat synthesis require acetate and hence low fiber diets lead to milk fat depression. Starch and sugars yield propionate as end prod­uct. The propionate converts to succinate and enters Krebs cycle producing glucose through gluconeogenesis. Propio­nate contributes to most of the energy required for weight gain and lactose production. Rapidly fermentable carbohydrates such as cereal grains lead to increased propio­nate proportion. Feeding inadequate amount of grain-based concentrate may decrease the lactose and overall milk pro­duction. As the propionate is glucogenic, the acetate and butyrate are ketogenic producing ketone bodies such as ace­tone, acetoacetic acid, and beta hydroxy butyric acid, ulti­mately contributing the energy needs of ruminant animals. The ketone bodies are used by skeletal muscles and other body tissues as a source of energy for fatty acid synthesis. Butyrate acts as energy source for rumen epithelium. It stimulates epithelial cell proliferation, consequently improv­ing feed utilization. The concentration of butyrate signifi­cantly increases with increased concentrate feeding.

14.4.3 Protein Digestion in Ruminants

The rumen microbes utilize nitrogen and prepare their own sequence of amino acids for their growth and multiplication. The protein metabolism in ruminants depends upon the abil­ity of rumen microbes utilizing ammonia. In ruminant nutri­tion, proteins can be divided into rumen degradable protein and non-degradable protein. The non-protein nitrogen substances are entirely degradable proteins. Of the protein consumed, depending upon the source, 20-100% will be degraded to ammonia. The rumen degradable protein fraction is hydrolyzed by extracellular proteolytic activities yielding short-chain peptides. Energy is a limiting factor determining the fate of absorbed peptides and amino acids. In the case of energy availability, the amino acids will be transaminated and used for microbial protein synthesis. In the event of energy deficit, the amino acids will be deaminated with the resulting carbon skeleton fermented into volatile fatty acids. Deamination causes the release of ammonia and carbon skel­eton; the latter enters into various steps of VFA pathways, consequently producing acetic, propionic, and butyric acids. The rumen undegradable protein escapes ruminal microbial degradation reaching small intestine for enzymatic digestion.

14.4.3.1 Nitrogen Metabolism in Rumen

The protein requirement of ruminants met by the microbial protein. On total nitrogen basis, rumen bacteria contain about 65% protein. For every 1 kg organic matter digested, the microbial yield ranges from 90 to 230 g, which is sufficient for growth and production to certain extent. The peptides are generally absorbed by microbial cells. The efficiency of nitrogen incorporation into bacterial protein is higher for peptides. Whereas the individual amino acids will be subjected to rapid deamination producing NH₃ for bacterial growth along with CO₂ and volatile fatty acids. The pathways of digestion and metabolism of nitrogenous compounds in ruminants is presented in Fig. 14.8.

The bacteria synthesize protein by utilizing certain portion of true protein and entire non-protein nitrogen compounds such as urea. The urea includes urea from diet, saliva, and rumen epithelium. The protein degradation depends on die­tary (structure, solubility, number of disulfide bonds and cross linkages between amino acid) and ruminal (type of bacteria, species, ammonia concentration, and pH)

Fig. 14.8 The pathways of digestion and metabolism of nitrogenous compounds in ruminants. [The proteolytic bacteria break down the amino acids into ketoacids and ammonia, which in turn is used to prepare microbial protein]

conditions. The bacteria producing highest proteolytic enzyme concentration include Butyrivibrio sps., Bacteroides sps., Selenomonas sps., Succinivibrio dextrisolvens, and Megasphaera elsdenii.

More than 80% of the rumen bacteria utilizes ammonia as nitrogen source for growth. The concentration of ammonia nitrogen in rumen liquor varies with the diet from as low as 2 mg/dL in low-protein diets and as high as 100 mg/dL in high-protein diets. Urea in diets is converted by ureolytic bacteria to ammonia. Although the ruminants are able to utilize NPN compounds such as urea, the urea poisoning is not an uncommon phenomenon. Urea poisoning is mainly because of consuming higher quantities of urea, consequently increasing rumen pH and ammonia absorption rate into blood stream.

14.4.3.2 Metabolism of Amino Acids

Certain reactions occur for synthesis of non-essential amino acids, interconversion of amino acids, energy production, and ammonia excretion. These reactions include transamination, deamination, and decarboxylation.

14.4.3.2.1 Transamination

Transamination refers to a process whereby amino groups are removed from amino acids and transferred to acceptor ketoacid without the intermediate formation of ammonia. The most common transaminases are alanine transaminase and aspartate transaminase.

14.4.3.2.2 Deamination

Deamination refers to a process of removal of an amino group from an amino acid. The reaction is catalyzed by deaminases. They are of either oxidative or non-oxidative type.

Oxidative deamination: Oxidative deamination is a form of deamination involving oxidation in the conversion of amino acid to ketoacid and amino group to ammonia.

Non-oxidative deamination: Non-oxidative deamination refers to the deamination process involving non-oxidative steps and is catalyzed by amino acid dehydratase.

14.4.3.2.3 Decarboxylation of Amino Acids

Decarboxylation refers to reactions involving the removal of a carboxyl group from amino acids releasing biogenic amines and CO₂. The decarboxylases may be either specific or nonspecific.

14.4.4 Lipid Metabolism in Rumen

The uniqueness of lipid metabolism in ruminant calves is the presence of pregastric esterases in saliva, providing the

Fig. 14.9 Ruminal metabolism of lipids. [Lipolytic bacteria of rumen cause the breakdown of triglycerides into glycerol and free fatty acids and the galactolipids into galactose and free fatty acids]

ability to start digestion of milk fat from mouth. Dietary lipids include structural lipids of forages and storage lipids of oil seeds. Majority of the lipids in forages are phospholipids, whereas the oil seeds mainly comprise lipids as free fatty acids. A typical ruminant diet contains unsatu­rated fatty acids at higher proportion. They may be either from the galactolipids of forages or triglycerides of cereal grains and oil seed cakes. The rumen microbes hydrolyze the galactolipids and triglycerides to free fatty acids and glycerol. Glycerol is fermented to propionic acid. The ruminal metab­olism of lipids is shown in Fig. 14.9.

The metabolism of lipids by rumen microbes involves a four-stepped process.

14.4.4.1 Hydrolysis of Esterified Fatty Acids

The triglycerides are hydrolyzed to fatty acids through hydro­lysis. The lipids are subjected to hydrolysis by microbial lipases viz. cell bound esterases and lipases produced by rumen bacteria. Feeding concentrates at higher levels leads to production of higher concentration of unesterified fatty acids. Less than 10% of polyunsaturated fatty acids escapes the ruminal hydrogenation.

14.4.4.2 Biohydrogenation of Unsaturated Fatty Acids

The unsaturated fatty acids are biohydrogenated to saturated fatty acids. The linolenic acid of grasses is rapidly converted in rumen producing stearic acid, cis-transmonoenoic acid, and cis-trans dienoic acid as end products. Incomplete biohydrogenation generally produces conjugated linoleic acids (CLA), which are proven to benefit human health. Although the biohydrogenation abil­ity is found in both bacteria and protozoa, the extent varies with higher ability in ruminal bacteria such as Ruminococcus albus and Butyrivibrio fibrisolvens. The biohydrogenation procedure is continuously monitored by the presence of metabolic hydrogen as end products of carbohydrate fermentation.

14.4.4.3 Lipid Biosynthesis in the Rumen

The ruminal fauna, especially bacteria synthesize odd chain fatty acids from propionate and branch chain fatty acids from valine, leucine, and isoleucine. The presence of odd chain and branch chain fatty acids in milk and higher stearic and oleic acids of ruminant fat depots are related to the biohydrogenation and rumen synthesis of fatty acids.

14.4.4.4 Metabolism of Phytal to Phytanic Acid Phytal is an isoprenoid alcohol present in the chlorophyll of leaves. On consuming forages, the ruminant bacteria hydro­genate phytal to dihydrophytal, consequently producing phytanic acid on oxidization. The resultant phytanic acid is incorporated into rumen organisms and is reported to activate the transcription factors.

14.4.5 Lipid Digestion in Small Intestine

The short-chain fatty acids are mostly absorbed from rumen wall. The lipids leaving the rumen include 85-90% free fatty acids and 10-15% phospholipids. The neutral pH conditions render most of the free fatty acids assaults of calcium, sodium, and potassium. Reaching the acidic abomasal pH conditions dissociates the free fatty acids from the minerals. The free fatty acids adsorb on the degraded feed particles and pass to duodenum through pylorus.

In non-ruminants, monoacylglycerols play an important role in the formation of micelles. However, in ruminants, lysophosphatidyl choline acts as emulsifying agent. Micelle of saturated fatty acids forms under the influence of bile salts and lysolecithin. The pancreatic phospholipase hydrolyzes lecithin into a fatty acid and highly polar lysolecithin. The higher percent of lipid absorption occur in lower part of the jejunum. The bile salts are absorbed in ileum and reaches back to liver to contribute to bile. After entering into mucosal cells, resynthesis of triglycerides occurs via the glycerophosphate pathway. The triglycerides combine with the proteins inside the Golgi body to form chylomicrons. The chylomicrons and very low-density lipoproteins (VLDL) are carried to adipose tissue by capillaries.

Learning Outcomes

Ruminants possess large compartmental gastro­intestinal tract viz. rumen, reticulum, omasum, aboma­sum, and intestine, which favors handling large amounts of fibrous plant materials. In adult ruminants, the rumen harbors vast range of microbes enabling microbial fermentation of ingesta before exposing to gastric juices of abomasum. The fermentation of com­plex carbohydrates produces short-chain fatty acids (acetate, propionate, and butyrate), and gases such as CO₂, CH₄, and H₂. The protein metabolism in ruminants depends upon the ability of rumen microbes utilizing ammonia to produce microbial proteins. Ruminal bacteria split the fatty acids and sugars from glycerol backbone through lipolysis. The metabolism of lipids by rumen microbes involves a four-stepped process viz. hydrolysis of esterified fatty acids, biohydrogenation of unsaturated fatty acids, lipid bio­synthesis in the rumen, and metabolism of phytal to phytanic acid.

Exercises

Objective Questions

1. The juice which plays an important role in the digestion

of fats is_____________.

2. The feedstuff that is regurgitated and remasticated in

mouth of ruminants is ______.

3. Important parameter that stimulates chewing activity and

saliva production is________.

4. An example for lipolytic bacteria is____________.

5. Rumen Holotrichs use_________ and entodinomorphs

utilize__________ for survivability.

6. _________ are able to penetrate the cuticle and

degrade plant cell wall.

7. The roughage fraction composed of beta-linked

galacturonan structure is ______.

8. Feeding roughage and concentrate-rich diets leads to the

production of_________ and___________ as fermenta­

tion end products, respectively.

9. The first step of bacterial degradation of carbohydrate is

10. ______________ reaction of pyruvate causes the for­

mation of acetic acid and formic acid from two molecules of pyruvic acid.

11. ____________ is an example for hydrogen sink in

rumen.

12. The ratio of acetate, propionate, and butyrate ranges from for high forage diets.

13. Feeding rapidly degradable starch substances at huge

level may leads to__________.

14. _ is the desired carbohydrate fermentation

end product for milk fat synthesis.

15. _ is the desired carbohydrate fermentation

end product for weight gain and lactose production.

16. _ acts as energy source for rumen epithelium.

17. On total nitrogen basis, rumen bacteria contain about protein.

18. During lipid metabolism, glycerol is fermented to volatile fatty acid.

19. is an isoprenoid alcohol present in the chlo­

rophyll of leaves.

20. The short-chain fatty acids are mostly absorbed from

Subjective Questions

1. Explain in detail about the mechanical factors involved in ruminant digestion.

2. Write about the microbial habitat of rumen and classify the bacteria according to the substrate.

3. Elucidate the metabolic pathways of pyruvate degradation.

4. Explain clearly the pathways of digestion and metabolism of nitrogenous compounds in ruminants.

5. Describe the role of rumen biohydrogenation procedure in lipid metabolism.

Answers to Objective Questions

1. Bile juice, pancreatic juice

2. Lighter roughage pieces

3. Physically effective NDF

4. Micrococcus sps.

5. Soluble sugars and starch

6. Fungi

7. Pectin

8. Acetate and propionate

9. Adherence

10. Carbon dioxide fixation

11. Propionate, sulfate, and nitrate

12. 70:20:10

13. Subacute rumen acidosis

14. Acetate

15. Propionate

16. Butyrate

17. 65%

18. Propionic acid

19. Phytal

20. Rumen

Keywords for Answer to Subjective Questions

1. Mastication, deglutition, rumination, eructation, regurgi­tation, remastication, reinsalivation, redeglutition

2. Rumen fermentation, nitrogen metabolism, carbohydrate metabolism, cellulolytic bacteria, proteolytic bacteria, lipolytic bacteria

3. Phosphoclastic split, oxidative decarboxylation, acetyl Co-A, lactyl Co-A, acetate, propionate, butyrate

4. Non protein nitrogen, urea, microbial protein, rumen degradable protein, rumen undegradable protein

5. Triglycerides, galactolipids, glycerol, galactose, unsatu­rated fatty acid

Further Reading

Books

Duncan AJ, Poppi DP (2008) Nutritional ecology of grazing and brows­ing ruminants. In: Gordon IJ, Prins HHT (eds) The ecology of browsing and grazing. Ecological studies, vol 195. Springer, Berlin, Heidelberg

Hyder I, Reddy PRK, Raju J (2017) Alteration in rumen functions and diet digestibility during heat stress in sheep. In: Sejian V, Bhatta R, Gaughan J, Malik P, Naqvi S, Lal R (eds) Sheep production adapting to climate change. Springer, Singapore

McDonald P, Edwards RA, Greenhalgh JFD, Morgan CA, Sinclair LA, Wilkinson RG (2011) Animal nutrition, 7th edn. Pearson Education Limited, London, UK

Reddy DV (2021) Principles of animal nutrition and feed technology, 3rd edn. Oxford and IBH Publishing Co. Pvt. Ltd., New Delhi, India

Research Articles

Baldwin RL, Vi McLeod KR, Klotz JL, Heitmann RN (2004) Rumen development, intestinal growth and hepatic metabolism in the pre-and postweaning ruminant. J Dairy Sci 87:E55-E65

Fiorentini G, Carvalho IP, Messana JD, Canesin RC, Castagnino PS, Lage JF, Arcuri PB, Berchielli TT (2015) Effect of lipid sources with different fatty acid profiles on intake, nutrient digestion and ruminal fermentation of feedlot Nellore steers. Asian Australas J Anim Sci 28(11):1583-1591

Reddy PRK, Kumar DS, Rao ER, Seshiah CV, Sateesh K, Rao KA, Reddy YPK, Hyder I (2019a) Environmental sustainability assess­ment of tropical dairy buffalo farming vis-a-vis sustainable feed replacement strategy. Sci Rep 9:16745

Reddy PRK, Kumar DS, Rao ER, Seshiah CV, Sateesh K, Rao KA, Reddy YPK, Hyder I (2019b) Assessment of eco-sustainability vis-a-vis zoo-technical attributes of soybean meal (SBM) replace­ment with varying levels of coated urea in Nellore sheep (Ovisaries). PLoS One 14(8):e0220252

Shen H, Lu Z, Xu Z (2017) Associations among dietary non-fiber carbohydrate, ruminal microbiota and epithelium G-protein-coupled receptor, and histone deacetylase regulations in goats. Microbiome 5:123