Metabolic Disease: Acidosis Flashcards
What are production diseases caused by?
The metabolic demands of production and/or the unsuitability of conditions provided
Examples of production diseases
- Acidosis
- Ketosis
- Bloat
- Milk Fever
- Tetany
Metabolic disorders
- A number of conditions exist that are influenced primarily by feeding management and diet formulation (nutrition)
Examples of metabolic disorders
- Acidosis
- Subacute acidosis (SARA)
- Liver abcesses
- Laminitis
- Bloat
- Ketosis
- Milk fever
What type of cows is acidosis most common in?
- High- producing dairy cows
- Given their high level of DM intake and the high proportion of cereals included in diets during lactation, it is quite common
- Also in intensive beef systems: mortality from acidosis in feedlot cattle is secondly only to that from respiratory diseases
Animals at risk from acidosis?
- Intensive finishing cattle on high concentrate diets
- Dairy cows and first calved heifer in early lactation
Subacute ruminal acidosis (SARA)
- Rumen pH: <5.5 in 3 out of 12 animals by rumenocentesis
What percentage of grazing dairy cows is SARA present in?
10-15%
What percentage of cows in confined high production systems is SARA present in?
20-40%
High quality grazed pasture
- Low DM concentration
- High digestibility
- High DM intakes from pasture eg 18kg of Grass DM per day = 2.3 kg of sugar (especially for high yielding dairy cows)
Sward management
- Low sward heights presented to grazing cows
- Pastures managed to maintain high digestibility
- Swards not permitted to become long or fibrous
What is acidosis?
A condition in ruminants that is associated with feeding highly fermentable feed or poor feed management
What is lactic acidosis syndrome?
- Associated with large increases of lactic acid in the rumen
- Lactic acid accumulates in the rumen when the bacteria that synthesis lactic acid outnumber those that utilise lactic acid
What diets so acidosis result from?
- Diets that are high in ruminally available carbohydrates
- Forage that are low in effective fibre
Clinical signs of rumen acidosis
- Loss of appetite
- Death
3 effects of a fall in pH in the rumen
- Rumen movement stops and becomes atonic (loss of muscle strength) which depresses appetite and production
- Change in acidity alters the rumen microflora with lactic acid bacteria proliferating
- This leads to more acid being produced and increasing acidosis
At what pH is the rumen fluid too low>
< 5.5
Why does the pH drops?
- Fermentation of CHO produces acids which lower ruminal pH
- Buffer systems (saliva) normally keep pH between 5.8 and 7
- If pH drops below this, acidosis occurs
- The lower the pH, the worse the problem
pH for subclinical acidosis
< 5.5
pH for acute acidosis
< 5.0
Causes of acidosis
- Brought about by the build up of lactic acid in the rumen
- Results from the fermentation of high CHO (concentrate) diet
- VFA production increases with a concomitant drop in pH (also reduced rumination and thus saliva flow)
- As pH drops, growth of lactic acid producing bacteria increases relative to other bacteria
What happens when the pH is equal to 5.5?
There is a balance between lactate producers and utilisers
What happens if the pH drops below 5.5?
Lactic acid accumulates and pH declines further
What happens if the pH goes below 5?
Lactobacilli species predominate
What happens if lactic acid is absorbed by the rumen?
Systemic acidosis
Pathophysiology
- Ingestion of carbohydrates in excess of rumen fermenting capabilities results in a decrease in pH
- This decrease in pH kills protozoa and microbes but favours lactic acid producing bacteria
- The pH continues to fall with further production of D and L lactic acid
- L lactic acid is metabolised, D lactic acid cannot be and builds up, leading to acidosis
Are high concentrate diets high risk?
- Yes, especially when introduced without proper adaptation
- Low levels of NDF from forage
- Higher level and rate of VFA production
- Reduced saliva production
Are diets high in starch/ sugars high risk?
- Yes
- Rapidly digested concentrates have greatest risk (wheat/barley >pulp)
Steps for care with ad-lib feeding
- Introductory period (1-2 weeks)
- Animals require 1kg DM roughage: 10% of diet
- Keep meals in front of stock at all times
- Rations type ( mixture of energy sources, protein source, rolled vs ground cereals)
What effect does minimal processing of barley have on ruminal digestion?
- Slows ruminal digestion
- ie merely cracking the pericarp or hull
- Optimal level of processing should maintain an acceptable level of grain digestion in the total tract
What happens when there is repeated bouts of SARA?
- Future problems
- Can lead to impaired animal health, including decreased feed intake and milk fat production
- Lowered body condition
- Inflammation
- Liver abscesses
- Displaced abomasum
- Laminitis causing lameness
What happens in the rumen when there is severe rumenitis?
- Ruminal papillae increase in length when cattle are fed higher grain diets
- This increases ruminal surface area and absorptive capacity, which protect the animal from acid acumulation in the rumen
- If the absorption of these cells is impaired, it becomes more difficult for the animal to maintain a stable ruminal pH following a meal
- Inflammation of the ruminal epithelium (rumenitis) could cause pain and contribute to intake depression during subacute ruminal acidosis
Cultural independent molecular techniques
- PCR- DGGE
- Sub-cloning sequencing
- Quantitive PCR
- Next generation sequencing 454 pyrosequencing
Do rumen microbes require and anaerobic enviornment?
- Yes
- They are also unculturable
Diet strategies to control acidosis
- Gradual adaptation
- Diet formulation and fibre
- Monitor the inclusion level
- Sorting
Diet Strategy: Gradual adaptation
Gradual transition of cows from a high forage dry cow diet to a lactation diet helps to stabalise the rumen environment to dietary change
Diet strategy: Diet formulation and fibre
Target a minimum of 25% NDF in the total diet, 75% of which is supplied by coarse forage to maintain rumen function and health
Diet strategy: Monitor the inclusion level
Rapidly fermentable ingredients like wheat, barley and steam-flaked grains. Also wet silage and/or low pH (<4) silages can increase the acid load
Diet strategy: Sorting
To reduce sorting, prepare TMR with an appropriate particle size and moisture content
- Dry diets not only limit feed intake, they also help to prevent excess sorting.
- Ideal moisture content in TMR is about 40-50%
Pasture-based diets and subacute ruminal acidosis
- A common source of energy supplementation is cereal grains with wheat being used by some
- Most practice abrupt introduction to pasture post- calving
- Often huge variation in diet where cows are housed again for 1 day, 2 days or 1 week due to poor weather or poor soil conditions in spring
- Little opportunity to introduce supplements eg forages and buffers
- Rumen fill is often lacking
Non fibre carbohydrate
- Starch
- Sugar
- Pectin
- Volatiles
Fibre carbohydrates
- NDF: cellulose, hemicellulose, lignin
- ADF: cellulose, lignin
Too little fibre in the diet?
- Rumen pH decreases
- Digestibility is impaired
- Low milk fat %
- Laminitis
Too much fibre in the diet?
- Reduced ration energy density
- Reduced dry matter intake
- Low milk yield
- Reduced BCS gain
Forage fibre required in a winter milking diet
- Minimum NDF 28-34%
- At least 75% from forage
- Higher with increased CHO degradability
Forage fibre required in a grazing herd diet
- Minimum NDF 30-32%
Forage fibre required in a dry cow diet
- Minimum NDF 38-40%
NDF content of grazed grass in spring
35-40%
Effective NDF content?
14-20%
Effective NDF requirement at grass
17%
eNDF of perennial ryegrass?
40-50% of total NDF
Housing management and environment
- Nutritional imbalances, deficiencies or erratic management of feeding should be avoided at all costs
- Housing requirements, ensure adequate trough space (0.6m/cow)
- Avoid factors such as limited water availability, poor grouping strategies/overcrowding, excessive time standing after milking and slippery floor at the feed face
