Hypomagnesaemia in Large Animals Flashcards
(32 cards)
1
Q
Role of Mg in body
A
- intracellular cation responsible for intracellular signaling
- extracellular: nerve transmission, motor endplate w/ Ach, hyperexcitability -> Tetany
2
Q
Mg Storage & Use in Ruminants
A
- vast majority inaccessible
- SI = site of net secretion
- SI excretion, susc to any changes in diet Mg
- XS lvls excreted in urine
3
Q
Mg homeostasis
A
- No FB mechanism/homeostatic mechanism to regulate Mg in ruminants
- Conc det’d by: [Mg(serum) = (Mg(absorption)) - (Mg(loss))]
- variable due to intake
4
Q
Mg Absorption
A
- Dietary K+ depolarises apical membrane of ruminal epithelium reducing Mg absorption
- Absorption = main component responsible for Mg variation
- Rumen = main site in adults; net secretion from SI
5
Q
Rumen Transport of Mg for absorption is dependent on
A
- conc of Mg in soln
- Integrity of Mg active transport system (Na-linked): lush high moisture spring pasture - low in diet Na, high in K
6
Q
Mg loss in ruminants
A
- mediated by kidney
- increased reabsorption w/ elevated PTH (indirect)
- ONLY in hypermagnesaemia
7
Q
Epidemiology & risk factors
A
- affects dairy & beef cattle
- age: 4-7 yrs
- stage of lactation: 1st 2 mos
- Stress: modifiable
8
Q
Dietary risk factors
A
- forage type/conservation - grass < silage
- Fertiliser - type & intensity of application
- Grass species (Mg content)
- Cereals
- Seasonality - Autumn/spring
- low energy feeds
- increased RDP
- Interactions of Na: Mg absorption Na-linked, increase K
9
Q
Peracute Clin signs hypoMg
A
- Sudden death
- found dead
10
Q
Acute HypoMg is an
A
EMERGENCY
11
Q
Acute HypoMg clin signs
A
- stop eating, muscle twitching, fall to ground
- opisthotonus
- hyperexcitability
- Nystagmus
- spasm of masticatory muscles
- frothing at mouth
- pricked ears
- retraction of eyelids
- clonic convulsions of limbs, seizure-like, paddling
- extensor rigidity
- periods of calm, loud tachycardia
- often hypermotile rumen & D
- Death in 30 min - 1 hr
12
Q
Subacute clin signs of HypoMg
A
3-4 day course
* excitable
* vocal
* ‘spasmodic’ urination
* increased freq of defecation
* marginal Mg status, where stressful even may push to acute
* ‘Behaving oddly’
13
Q
Chronic/subclinical HypoMg
A
- uncommon Dx
- Non-specific: ill thrift, reduced milk yld, dullness
- occasional sudden death in herd
14
Q
Dx of HypoMg
A
- Hx
- Clin signs
- Reponse to txt
- Serum Mg sample if warranted
- PM - Dx difficult (Vitreous/aqueous humor samples up to 72 hrs after death)
15
Q
Differentials for Hypomagnesaemia
A
- Stage 1 hypoCa
- Nervous ketosis
- BSE - response to txt rules out
- Listeriosis
- Pb poisoning - recumbency common sign
16
Q
Blood biochemistry
A
- Mg levels
- Ca often low
- K often high if clinical
17
Q
Treatment of Hypomagnesaemia
A
- if convulsing: SEDATE
- Na pentobarbital (20%) 5-15 ml slowly IV
- monitor heart continuously
- Follow w/ 400 ml 20% Ca borogluconat-Mg hypophosphate sln slowly IV
- 400 ml 25% MgSO4 sln SQ
- use flutter valve & 14G needle
- DON’T KILL THE COW BY REVERSING ORDER
18
Q
How to sedate a convulsing cow
A
- A2 agonist - Xylazine (note: lowers seizure threshold)
- Diazepam & Pentobarbital = Anti-convulsions (under cascade), incl. Euthatol if necessary
19
Q
Hypomagnesaemia txt & case mgmt
A
- achieve sedated animal that is no longer twitching/convulsing
- place in sternal recumbency
- provide shelter
- should be standing/normal in 12-24 hrs; if not = poor prognosis
- 60 mg MgO orally in at risk period & cohorts
- Examine entire herd policy - iceberg
20
Q
Prevention of hypomagnesaemia
A
- risk periods
- Provision of supplemental Mg in at-risk periods
- feed supplements
- pasture dusting
- Mg Bullets
- Mg in drinking water
- Oral supplementation of Mg
21
Q
Risk periods for hypomagnesaemia
A
- 6-8 wks after going to grass in spring
- winter milk herds on lush autumn aftermath
- sept-March in outwintered sucklers
- transit tetany
22
Q
Ideal dosing of Mg supplement in at-risk period
A
~30 g of Mg/cow/day (= 60 g MgO)
23
Q
Issues with Mg supplement lie with
A
appropriate delivery
24
Q
Supplementing Mg in feed
A
- palatability = poor
- Mg inclusion in concentrates = V. SUCCESSFUL
- Available Mg depends on amt & conc of ration
25
Never feed high Mg feeds to...
calves, drystock, sheep
Causes urolithiasis
26
Mg licks
* 'bitter taste' - can mask w/ molasses
* variable intake per cow
* hierarchy w/i herd/dominance issues over bucket can impact those lower down in hierarchy
27
Pasture dusting of Mg
* environmental concerns (runoff, etc)
* only economical if stocking rate is 1+cow per acre
* Grass cover must be >/= 10 cm
* Need 20-35 MgO per hectare
* Issues w/ RAIN making it go away!
28
Mg Bullets
* each bullet released <1g Mg/d
* problem w/ retention
* inadeq in severe deficiencies
* sucklers these are used often
29
Mg in drinking water
* will avoid if another source of water can be found
* gives 20-40 g Mg/cow/day as soluble salt - prevents tetany in Spring/Autumn
* >40g = D
* impacts taste
* ltd by variability in water intake per cow
* cows have little or no water intake in wet weather
* must be no other water sources for them to be willing to ingest it
30
Other ways to prevent HypoMg
* avoid K application in spring (prev. autumn)
* supply Na licks
* avoid stress
* provide shelter
31
Oral supplementation of Mg
* if no concentrate feeding -> sprinkle MgO BID on silage
* if hay -> dampen before sprinkling to get proper supplementation
32
HypoMagnesaemia in calves
* uncommon
* calves 2-6 mos of age, on milk (Mg low in milk, must supplement)
* Mg initially absorbed from SI in calves (adults SI is for excretion) -> absorption declines by 3 mos of age; exacerbated by D assoc'd w/ Cu def; more able to mobilise Mg than an adult
