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When is rumen pH usually at it's nadir?
3-4 hours post eating
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Rumen pH is driven by __________; magnitude of rumen pH drop depends on...
carbohydrates; how much the animal eats, how much grain is in the diet, what type of feed the grain/ carbs comes from (rapidly fermentable non-fiber carbs, like corn, results in rapid production of VFAs).
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SARA in feedlot animals is usually a consequence of ___________; SARA in dairy cattle is usually a result of __________.
lactic acid; VFAs
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How is SARA defined? (5)
- rumen pH at 3-4hr post-feeding
- mean pH from several time points
- minimum pH over 24 hours
- hours below a certain pH (depends on method of sampling)
- area under the pH time-curve
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Under field conditions, __________ is NOT a definitive diagnostics.
rumen pH
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How does the method of rumen fluid sampling affect the pH value you get?
- rumenocentsis usually results in a lower pH value than rumen cannula (they are not perfectly correlated)
- rumen cannulated sample from multiple areas of the rumen (fiber mat, liquid, etc) is most accurate but also not feasible in all situations
- sample taken by stomach tube is almost useless; saliva contamination greatly increases pH, don't know what part of rumen is being sampled
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How can you use rumenocentesis to diagnose SARA on a farm?
- sample at least 10-12 cows within a group ~4 hours after feeding
- all pH >5.8 normal
- 3 or more cows <5.5 abnormal
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What are clinical observations associated with SARA? (6)
- low milk fat
- poor feed efficiency (low milk:DMI ratio)
- variable DMI
- diarrhea
- low BCS relative to diet
- too many hoof horn lesions (DELAYED response)
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Rank common grains from slowest to fastest rate of fermentation.
- [slowest] sorghum
- corn
- barley
- oats
- wheat [fastest]
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Rumen pH is a function of... (4)
- acid production
- acid intake
- acid removal
- buffering capacity
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What is rumen acid production affected by?
type and amount of carbs in the diet
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What is acid intake affected by?
silage/ high-moisture corn, alfalfa balage in the diet--> leads to VFAs and lactic acid in the rumen
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What is rumen acid removal affected by?
- DMI--> rate of passage
- pH
- rumen size, papillae--> greatly increase surface area for absorption (basis behind hot diet in late lactation to elongate rumen papillae)
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What diets foster longer rumen papillae?
high grain diets
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What is rumen buffering capacity affected by?
feeds/ chewing/ physically effective fiber--> saliva production with bicarb
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How much of the diet is usually supplemental rumen buffer, such as sodium bicarb?
- 0.8% of diet
- 0.4# of buffer in a 50# DMI diet
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Most of the acid in a diary cow's rumen comes from...
bacterial production of VFAs
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Preventing rumen acidosis is a balance between _________ and __________, which includes...
- acid production and buffering
- acid production- amount of NDF and NFC, grain processing, and type of grain
- buffering- amount of NDF, physical form of feed, buffer supplements, and buffering in feeds
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What feeds cause the most acid production within the rumen to least? (7)
- [highest acid production] wheat, barley, steam-flaked corn
- high-moisture corn
- finely ground corn
- coarsely ground corn
- starchy byproducts (middlings)
- high quality forages, byproducts
- [least acid production] low quality forages
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What aspects of a diet do you examine when evaluating for SARA?
- %NDF
- %forage NDF
- %NFC
- %starch
- %DM (may affect sorting, forage quality)
- source of starch
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What is a feed management principal that can lead to SARA?
over-mixing, feed particles too small
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When should you make sure to increase NDF in a diet? (4)
- feeding high moisture corn, wheat, barley, or steam-flaked corn
- forage particle size is too small
- grain fed separate from forage (robotic milker, PMR)
- feeding management is not great
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What are 3 aspects of rumen buffering and factors affecting each?
- Saliva: dry coarse feed (most saliva)> wet coarse feed>> small particles (least saliva)
- Feeds: Ca, Mg (contibute most to rumen buffering)> protein> fiber>> starch (does not buffer the rumen, contributes to acid production)
- Supplemental buffers: sodium bicarb
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How much salt should be in a TMR (% of diet)?
0.5% of diet
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When do DAs usually occur and when is the risk for this?
- usually you see DAs clinically in early lactation (up to 14 DIM)
- the risk for DAs should be addressed in late lactation, close-up dry cows
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Symptoms of DA?
- off-feed
- down in milk
- scant stool
- ketosis
- mild alkalosis
- ping
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What are factors contributing to DAs?
- hypocalcemia is a major risk factor- decrease smooth muscle tone of abomasum, abo atony
- NDFs, forage NDFs, soluble carbs (NFC), Calcium- all contribute to rumen function, fermentation, rate of passage, keeping rumen full
- increased VFAs--> increased absorption of VFAs--> increased VFAs move to abo, causing decreased motility/ atony and fermentation/ gas in abo
- physical space created in abdomen after calving and with empty rumen d/t off feed
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Predisposing factors for a DA? (6)
- low DMI
- low intake of physically effective fiber
- excessive intake of rapidly fermentable carbs
- BCS >3.5 at calving
- sudden decrease in DM or NDF of forages
- other metabolic diseases (ketosis, milk fever, RFM, metritis)
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What are the consequences of DAs? (5)
- decreased milk income
- increased incidence of other disorders
- decreased herd life
- increased costs
- risk os re-occurence
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What is the goal for incidence of DAs in a herd?
<5%
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What factors contribute to the cost of a DA? (2)
- loss of milk *****
- treatment costs
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