ruminant nutrition

Definition and Characteristics of Ruminants

• Order Arteriodactyla – the even-toed ungulates

  • Suborder ruminantia

• Ruminant comes from a Latin word meaning to chew again, referring to cud-chewing exhibited by ruminants

  • Contrast to other herbivores that do not regurgitate feed for repeated chewing

• Counting domestic, feral, and wild, ruminants are most important herbivores in terms of numbers in the world

• Ruminants are found from arctic to tropical habitats

Importance of Ruminants

• Capable of utilizing fibrous feedstuffs

• Less competition for food with humans

  • Herbivorous

  • Can be supported on vegetation from land that can’t support other crops

• Agricultural importance

  • Sheep domestication 11,000 years ago; goats 9,000 years ago; cattle 8,500 years ago

• Food production for humans – meat, milk, fiber, work – draft

  • 940 million – 1.4 billion cattle (second most abundant)

  • 1 billion sheep (third most)

  • 720 million goats (fifth most)

  • Other domesticated ruminants – buffalo, camels, alpacas, llamas, reindeer, yaks

Ruminant Adaptation

• Cattle – world-wide

  • Arctic: great utilization of reindeer and yaks

  • Wet, tropical areas: more buffalo

• Drier areas

  • Sheep, goats, camels

• Alpacas and llamas – central and south America

Ruminant Feeding Types

• Concentrate selectors or browsers

  • Select highly nutritious plants or selective of the highly nutritious plant parts and highly digestible

  • Many deer

• Grass and roughage eaters

  • Ability to digest more fibrous plant material than concentrate selectors

  • Grazing, grass eating species

  • Cattle, sheep – domestic and wild, bison, African antelope

• Intermediate, mixed feeders

  • Characteristics of both types

  • Potential for seasonal changes in diet that result in changes in feeding type

  • Elk, caribou

Dietary Habits

Ruminant Stomach

• 4 chambers or compartments, not 4 stomachs

Rumen Anatomy

• Ruminant stomachs have 4 compartments

  • Rumen

  • Reticulum

  • Omasum

  • Abomasum

• Illustration of the geography of the gastrointestinal tract of a cow by sides – note the rumen on the left side of the cow, orientation of the other compartments of the stomach, location of the intestine on the right side

Reticulum

• Not separated completely from rumen

• Aids in movement of food into the rumen or omasum

• Regurgitation of bolus during rumination

• Collects hardware and prevents movement

• Pictures of the surface of the reticulum and picture of example metal found in reticulums

Rumen

• Fermentation vat

  • Allows digestion of plant cell wall biomass

  • Main site of fermentation: reticulo-rumen (fermentation chamber)

  • ANAEROBIC

    • Low to no O₂

• Muscular walls aid in the mixing and movement of content (rumination)

• Absorption of VFAs and NH₃ through rumen wall

  • Surface covered in papillae

    • Absorptive structures for VFAs

Omasum

• Between rumen and reticulum

• Content must flow through to reach abomasum

• May be involved in particle size reduction and water absorption

Abomasum

• Connected to omasum

• Functions similarly to glandular stomach of nonruminants

• Mucus, HCl, enzymes secreted to initiate digestion

Rumination

• Four steps: regurgitation, remastication, reensalivation, reswallowing

• Spend ~8 hours/day ruminating

• Fibrous materials stimulate longer rumination time, longer retention

• Origin of ruminating not clear

  • Some thinking that it is a survival means of early ruminants – eat and hide

• Eructation: (belching) gas from microbial fermentation (12-30 L of gas)

• Two illustrations of the contents of the rumen – note the gas, fiber, and small particle layers

• Illustration of digesta flow through the compartments of the stomach of a cow – note ingestion flow as well as rumination (regurgitation) flow

• Rumen:

Rumen Digesta Movement

Pre-Ruminants

• Limited rumen development at birth

  • Milk-fed neonates, no need for fiber digestion

• At birth small, abomasum is the major compartment

• Esophageal groove routes milk to the acidic stomach

• With development and changes in diet, the rumen increases

  • 3-4 months starts to be dominant on volume

• Eventually overwhelming volume of the stomach is rumen

• Illustrations of the relative capacities of stomach compartments – note increases in rumen volume with increasing age

Rumen Development

• Diet influences the development of the rumen papillae and influences the feeding of calves transitioning from milk to higher fiber diets

  • Feeds that produce more VFA stimulate papillae development

  • With the presence of VFA, papillae expand and increase in size

Microbiology – Symbiosis

• True symbiosis between the ruminant and its rumen microbes

• Microbes of the rumen depend on the ruminant’s essential conditions

• Microbes are essential for digestion and fermentation of fibrous feedstuffs that could not otherwise be used for nutrients

• Ruminant provides habitat and microbes provide end products of fermentation

Rumen Characteristics

• Low oxygen environment:

  • 65% CO₂, 7% N₂, and 0.6% O₂ in the rumen

  • Trace CO₂, 78% N₂, and 21% O₂ in the atmosphere

• Lack of oxygen favors anaerobic microbes

• Dry matter content of rumen material varies from 6-18% depending on area in the rumen

  • Very fluid – facilitates microbial interactions and enzymes with feed

• Open and continuous ecosystem maintaining a stable microbial population

• Supported by a constant supply of substrates – eating feed – and a large holding capacity

  • Capacity aids in retention of complex diet components, allowing degradation and fermentation

• Carbohydrate rich

  • Cellulose and other polysaccharides make up most of the feed

• Large particles are retained until sufficient degradation has occurred

• Rate of passage – k_p

  • Amount of liquid and particulates that flow out of the rumen per unit time

    • Typically expressed as a percentage – 8%/h

Rumen Microbe Diversity

• Bacteria: digestion and fermentation of feed

  • 10¹⁰-10¹¹/mL bacteria

  • 0.3-50 um

• Protozoa: slow rate of pH decline

  • 10⁴-10⁶/mL ciliated protozoa

  • 20-200 um

• Fungi: attachment sites for bacteria

  • 10²-10⁴/mL fungal zoospores

Classifying Rumen Bacteria – By Substrate

• Cellulolytic – cellulose

• Hemicellulolytic and pectinolytic – hemicellulose and pectins

• Amylolytic – starch

• Proteolytic – proteins

• Ammonia producing – amino acid deamination

• Lipolytic – lipase producers

• Intermediate acid utilizers – lactate, succinate, formate

• Simple sugar users

Rumen Protozoa

• Majority are ciliated, but some flagellates

• Estimated to comprise 40% of microbial N and 60% of fermentation products

• Contribute to fermentation

  • Starch, sugars, pectin, hemicellulose

• Predators of bacteria

  • Consumed for protein

Anaerobic Fungi

• Attach to and found within plant fragments

• Contribute to the degradation of cellulose and other polysaccharides

MIcrobial Interdependence

• Intermediate cross feeding

  • Intermediates being metabolites produced through cell processes

  • Sharing of intermediates between species

    • End products of one become the substrate of another

  • An example:

    • Selenomonas ruminantium cannot use cellulose, but Bacteroides succinogenes does

    • B. succinogenes produces succinate and S. ruminantium can use the produce succinate

  • Another example:

    • Lactate production, sometimes associated with starch feeding, can be used by Megashaera elsdenii to produce propionate

• VFA requirements

  • Sharing some VFA among non-cellulolytic and cellulolytic bacteria

  • Production of branched chain VFA like n-valeric or 2-methylbutryric acids from deamination of branched chain amino acids by non-cellulolytic bacteria

  • Provide carbon skeletons

    • For synthesis of amino acids

    • But also for synthesis of microbial fatty acids with branched or odd numbered chains

      • Found in the cell membranes of bacteria

• Interspecies hydrogen transfer

  • In the rumen there are H₂ producing and H₂ utilizing species

  • Much of the H₂ is used to produce methane (CH₄) from CO₂

  • Transfer of H₂ to methane producers encourages more H₂ production

  • H₂ producing pathways are associated with greater energy production

    • Higher ATP yields by the bacteria support more bacterial growth and more microbial protein production

Fermentation – Substrates

• Not lipids

  • Hydrolyzed to free fatty acids and glycerol backbones, but not fermented in appreciable quantities

• Some protein/amino acid utilization

• Carbohydrates

  • Structural and non-structural

Carbohydrates

• Several sugars are found in hemicellulose

• Sugars

  • In feed or produced by polysaccharide hydrolysis

• Starch

• Pectins

  • Early structural polysaccharides of developing plant cell walls

  • “Glue” associated with carbohydrate cell wall

Variable Fermentation Rates

• Soluble CHO fermented first

  • Sugars, some starch

• Pectin next

• Structural CHO, cellulose last

  • Structural associated with more lignin, less digestible

• Easier to attack or hydrolyze substrates earlier and faster than harder to attack substrates

Fermentation

• ALWAYS FOLLOWS HYDROLYSIS

• Pyruvate is converted to VFA through pathways

  • Acetate production:

    • Pyruvate is first converted to acetyl-CoA

    • acetyl-CoA can then be converted to acetate

  • Propionate production:

    • Three main pathways for propionate production: succinate pathway, acrylate pathway, and propanediol pathway

  • Butyrate production:

    • Butyrate is typically produced from butyryl-CoA, which is derived from two molecules of acetyl-CoA

Short Chain Fatty Acids

• Butyrate: 2 hexose → 2 butyrate + 4 H₂ + 4 CO₂

• 3 hexose: 3 hexose → 4 propionate + 2 acetate + 2 CO₂ + 2 H₂O

• Acetate: hexose + 2 H₂O → 2 acetate + 4 H₂ + 2 CO₂

• Molar ratio:

  • Acetate:propionate:butyrate

  • 70:20:10 <60:30:8>

H₂ and CO₂

• Hydrogen and carbon dioxide production:

  • Hydrogen inhibits higher energy yielding pathways

  • See hydrogen transfer above

• Methane (getting rid of hydrogen):

  • 4 H₂ + CO₂ → CH₄ + 2 H₂O

  • Summation:

    • Hexose + 2 H₂O → 2 acetate + 4 H₂ + 2 CO₂

    • 4 H₂ + CO₂ → CH₄ + 2 H₂O

    • Summation: hexose → 2 acetate + CO₂ + CH₄

• Acetate from CO₂:

  • 4 H₂ + 2 CO₂ → 1 acetate + 2 H₂O

  • Summation: hexose → 3 acetate

Nitrogen Forms in the Rumen Related to Protein

• Typically think of protein as the nitrogen containing portion of the diet (contrast to carbohydrates and lipids)

• Remember true protein vs non-protein nitrogen

• Proteins contain amino acids and amino acids contain nitrogen

  • In the rumen: dietary protein as well as microbial protein

• Non-protein nitrogen also present in the rumen

  • Ammonia N

    • Dietary NPN or protein degradation

  • Urea N – originating from the blood

    • From the saliva or absorbed through the rumen wall

Classifying Dietary Proteins

• Classifying feedstuff protein according to its degradability in the rumen

  • Rumen degradable protein (RDP)

  • Rumen undegradable protein (RUP)

• Degradability determines how microbes interact with proteins – whether they modify them

  • Deaminate

Feed Protein Degradability Contrasts

• Proportion of protein degraded to ammonia N with residual reaching the small intestine intact

  • Rumen proteolysis by microbes

• Soybean meal – 84% – more degradable

• Cottonseed meal – 60%

• Alfalfa – 83%

• Blood meal – 31%

• Fish meal – 32%

• Meat meal – 35% – less degradable

Degradability of Protein Influences – Modifications Through Processing

• Processing feeds or modifying them can influence the degradability of protein by microbes of the rumen

  • Heat treating – forming crosslinks to limit accessibility

  • Coating or encapsulation – blockage of access

• Reversible modification to limit microbial access in the rumen, but allow access and digestion in the small intestine

  • Acid reversal in the abomasum and proteolysis by pancreatic enzymes

• Overprocessing (overprotection) can limit degradability too much

  • Not degraded in the rumen or the small intestine

• Some proteins are thought of to be less and more degradable

  • All proteins have degradable and undegradable portions

Protein for Absorption in the Small Intestine

• Protein entering the small intestine from two sources

  • Feed protein unmodified in the rumen

  • Microbial protein produced in the rumen

    • Microbes that leave the rumen and are digested

• Microbial protein is high quality (good amino acid profile) but likely insufficient to support highest levels of production

• Provision of additional high quality protein supports higher production

  • Some sources more likely to be modified in the rumen than others – degradability

• It is possible to find lesser producing animals lower quality proteins and meeting their requirements

Microbial Protein

• Rumen bacteria are about 50% protein by mass

  • Protozoa more variable but average 40% protein

• Depending on diet, intake, many factors – 40% of true protein entering the small intestine is microbial protein

  • A significant source of protein in ruminants

• Many rumen bacteria can use ammonia N to synthesize amino acids

  • From NPN in the diet

  • Hydrolysis of urea entering the rumen from the animal – nitrogen recycling

  • From protein degradation – deamination

Nitrogen “Recycling”

• Ammonia produced in the rumen or in the ruminant is converted to urea (1)

  • Urea produced in the liver (ammonia from amino acid deamination in the animal for example)

  • Urea could be excreted in the urine, or…

• Plasma urea crosses the rumen wall or incorporated into saliva and swallowed into the rumen (2)

  • Net effect is urea entry into the rumen

• Bacterial urease activity liberates ammonia from urea (3)

• Bacteria can use ammonia to produce amino acids and microbial protein (4)

  • Energy dependent process

  • Bacteria exit the rumen and amino acids absorbed to supply the host

• RECYCLING

Thought Question

• Is it possible for the flow of protein into the small intestine to exceed the amount of dietary protein fed?

  • Two sources: feed protein and microbial protein

    • Microbial protein can upgrade, take NPN from the animal and make new amino acids and protein

Take Non-Amino Acid N and Make Amino Acids

• NPN enters the rumen

  • NPN from the diet, NPN from the animal

• Some dietary protein degraded to ammonia by bacteria (RDP)

  • Some protein exits the rumen unchanged (RUP)

• Some protein is produced in the rumen from NPN

• Ammonia from NPN, from amino acid degradation (from RDP) is used to produce amino acids

• Protein entering the small intestine consists of dietary RUP and microbial protein from the rumen

Thought Question

• Can non-ruminant herbivores – like a horse or an elephant – recycle NPN to fermenting bacteria in their gut to produce amino acids for absorption?

  • Yes, cecum and large intestine in rabbits and horses can be specialized for microbial fermentation

Ionophores

• Modifiers of rumen fermentation

Rumen Modifying Compounds

• Compounds originally described as products of Streptomyces species

  • Transport cations across membranes

  • Examples available commercially: monensin, lasalocid

• Inhibit the gram positive bacteria of the rumen

  • Incorporate into cell membrane, allow flux of ions (loss of gradients)

• Modifying the bacteria populations fermentation

  • Increasing propionate

  • Decreasing methane production

  • Inhibiting proteolysis and deamination

• Improves fermentation products to support greater efficiency