2. rumen function and volatile fatty acid metabolism SDL

Question 1

describe the primary, secondary and rumination contractions in the reticulorumen including their sequences and functions

Answer 1

primary: (mixing)
- starts with biphasic contraction of the reticulum (2 contractions)
- followed by contraction wave moving caudally through the dorsal and ventral sacs of the rumen
- function: mixes ingesta to promotes microbial fermentation and ensures uniform distribution of feed particles and microbes

secondary: (erucation)
- initiated by the caudal part of the rumen
- wave moves cranially to facilitate expulsion of gasses
- function is to remove fermentation gases through erucation to prevent bloat

ruminantion contraction:
- coordinates contractions of the reticulum and rumen proel a bolus of feed uo the esophagus to the mouth for rechew
- function: reduce particle size and increase surface area for microbial action

Question 2

explain how the motility of the reticular-rumen is controlled

Answer 2

• neural via vagus nerve, coordinates motility patterns and responses to sensory inputs from stretch and chemo receptos in the rumen wall
• hormonal and chemical control via various GI hormones (motilin) and chemicals (VFAs) modulate activity of ENS and smooth muscles

Question 3

discuss the mechanisms that regulate the flow of ingesta from the reticulum to the omasum

Answer 3

• flow of ingesta from the reticulum to the omasum is regulated by the opening of and closing of the reticulo-omasal orifice
• only small particles and fluid can pass through the orifice. large particles are retained in the reticulorumen for further breakdown
• reticular contractions propel ingesta towards the reticulo-omasal orifice during the primary contraction cycle
• controlled by the vagus nerve which ensures synchronisation of contractions to facilitate selective passage

Question 4

what are the functions of the omasum

Answer 4

• absorption of water, electrolytes (Na) and VFAs
• further reduction of particle size from ingesta
• helps in buffering the flow of ingesta to maintain optimal pH for abomasal digestion

Question 5

outline the motility sequences of the omasum and how they contribute to its function

Answer 5

• omasum exhibits rhythmic contractions that squeeze the ingesta through the numerous leaves of the omenta, enhancing surface area for absorption
• these contractions controle the rate at which ingesta moves into the abomasum, ensuring a steady flow and preventing overloading

Question 6

describe the mechanism for the absorption of water in the rumen and explain why it is important for ruminant health

Answer 6

mechanism: water absorbed passively across the rumen epithelium via osmosis, driven by the omsmotic gradient created by the high concentration of the VFAs and other solutes in the rumen
importance: maintains fluid balance and prevents dehydration. essential for efficient microbial fermentation process

Question 7

Explain the mechanism for the absorption of sodium in the rumen and discuss its importance in maintaining rumen function.

Answer 7

mechanism: sodium is actively transported across the rumen epithelium via sodium-potassium ATPase pumps located in the epithelial cell membranes
importance: critical for maintaining osmotic balance and fluid volume in the rumen. sodium is also essential for varous cellular processes and electrical conductivity in nerve and muscle tissues

Question 8

Describe the microbial breakdown of complex polysaccharides to simple sugars in the rumen

Answer 8

• cellulose and hemicellulose are broken down by cellulytic and hemicellulytic bacteria into cellobiose and other oligosaccharides, then further into glucose and simple sugars
• starch is degraded by amylolytic bacteria to maltose and then glucose

Question 9

Explain how simple sugars are metabolized to volatile fatty acids (VFAs) by microbes in the rumen

Answer 9

• microbes ferment glucose through glycolysis to pyruvate which is then converted to VFAs such as acetate, propionate and butyrate
• produces VFAs and gases

Question 10

explain 3 ways which volatile fatty acids (VFAs) are absorbed in the rumen

Answer 10

1. primarily passive diffusion through the rumen epithelium (non ionized forms are more readily absorbed)
2. some may be absorbed through specific transport proteins in the epithelial cell membranes
3. bicarbonate ions in saliva help buffer the rumen contents to maintain optimal pH for VFA absorption

Question 11

Explain how the absorption of VFAs in the rumen is self-regulating and the significance of this regulation

Answer 11

• high concentrations of VFAs lower the rumen pH which slows down microbial activity and fermentation, reducing further the VFA production
• as VFAs are absorbed the pH of the rumen contents rises, enhancing microbial activity and VFA production ensuring stable environment for fermentation
• rumen epithelium adapts to increased VFA levels by increasing absorptive capacity which helps in maintaining homeostasis

Question 12

Summarise the advantages and disadvantages of ruminant fermentation and digestion as compared with non-ruminant

Answer 12

Question 13

List the principal differences in the forestomach and forestomach digestion between camelids and other ruminants?

Answer 13

• camelids have 3 compartments where ruminants have 4 (the 3 are named C1, C2 and C3)
• camelids primarily ferment in C1 whereas ruminants do it in rumen
• camelids have efficient water absorption in C1 and C2 whereas other ruminants = omasum
• camelids motility patterns have more segmented contractions, ruminants have distinct primary and secondary
• camelids have slightly different microbial populations adapted to their diet

Question 14

What are the features that permit continuous fermentation in ruminants?

Answer 14

• diverse microbiota capable of breaking down plant material
• anaerobic environment
• constant pH and temp
• continuous nutrient supply
• rumen motility (regular mixing)
• saliva production (buffering)
• efficient removal of VFAs and gas

Question 15

Why is the optimisation of rumen function important? How can this be achieved? How and why does suboptimal function occur and how can this be avoided

Answer 15

importance: maximises digestion and nutrient absorption, reduces risk of digestive disorders, enhances growth, milk production and overall efficiency
optimization: providing proper ratio of roughage to concentrate, maintaining consistent feeding schedules, regularly checking rumen pH, VFA levels and microbial balance, using buffers, probiotics and ionophores
suboptimal function causes: poor diet, abrupt changes, inadequate fibre, stress
consequences: acidosis, bloat, reduced efficiency, poor health
prevention: gradual diet transitions, balanced diet, monitoring of rumen health, stress management

Question 16

Why is forestomach motility important and how does it occur? What would happen if normal motility was interrupted or sub-optimal? How might this occur

Answer 16

importance: mixing, gas expulsion, digestion (fermentation)
mechanism: contractions controlled by vagus nerve and GI hormones
consequences: reduced fermentation, gas acumulation
causes: stress, nerve damage, dietary imbalances, illness

Question 17

What is the reticular groove reflex, why is it important and what stimulates it? What are the consequences of the reflex not occurring and why might this happen?

Answer 17

function: directs milk from esophagus to abomsum in young ruminants to bypass the rumen so no fermentation occurs
stimulation: triggered by suckling and noises from mom, reflex arc involves vagus nerve
consequence of failure: milk ferments leading to scour, inefficient nutrient absorption
causes of failure: stress, illness, improper feeding technique

Question 18

List the differences in forestomach function, physiology and biochemistry between ruminants fed on a diet composed solely of roughage and a diet composed predominantly of concentrate feeds with small quantities of roughage?

Answer 18