L13: Hypocalcemia And Micronutrient Deficiencies (Risco) Flashcards
All cows experience hypocalcemia around calving, but only 6% develop clinical signs (milk fever)
25-50% of cows have sub-clinical hypocalcemia during first 12 days pp
-use of anionic diets most common cause
What is considered hypocalcemic?
Ionized calcium is about what percent of total calcium?
50% (ICa is physiologically active)
Why does Ca drop right before parturition?
- sequestering Ca for colostrum, and last phase of fetal skeletal growth
- majority of Ca is not available in plasma, therefore they can become hypocalcemic very easily
What does 1-alpha hydroxylase do?***
Converts inactive vit. D (1,25-dihydroxyvitamin D) to active form (Calcitriol)
Where is 1,25-dihydroxyvitamin D stored? Functions?
In the liver
- when PTH is released, gets converted to active form (calcitriol) which acts to resorb bone calcium and actively absorb dietary Ca
- “if you measure the vitamin D of a cow 188 DIM, you will be measuring the INACTIVE form. But when animal is in hypocalcemic crisis, vitamin D will be in active form.”
Etiology of hypocalcemia
- acute loss of Ca in colostrum at first milking is not resolved by influx from intestine or bone
- amt. of labile bone Ca and # of Vit. D receptors decreases with age
- Jersey cattle have fewer Vit. D receptors
Dietary cation anion difference ***
-influences blood acid/base status that affects calcium homeostasis
DCAD = (Na+K) - (Cl + S)
- cationic prepartum diet is higher in cations and results in a METABOLIC ALKALOSIS that depresses tissue response to PTH
- anionic prepartum diet (higher in anions) results in METABOLIC ACIDOSIS which upregulates PTH receptors in concert w/ blood buffering mechanisms, and Ca carbonate is released from bone. Ca in blood increases and carbonate is available to buffer the excess H+ ion concentration
Posture, attitude, and pulse of stage 1 hypocalcemia
Posture: ataxic, standing, unsteady
Attitude: alert, excited
Pulse: normal, muffled
Posture, attitude, and pulse of stage 2 hypocalcemia
Posture: sternal recumbency
Attitude: alert to depressed
Pulse: increased (90 bpm) and weak
Posture, attitude, and pulse of stage 3 hypocalcemia
Posture: lateral recumbency w/ complete muscle flaccidity
Attitude: depressed to comatose
Pulse: rapid (>110), weak, muffled
Milk fever = the gateway disease to:
- mastitis
- DAs
- metritis
- ketosis
- etc.
Therapeutic considerations for hypoCa
- clinical (milk fever) requires parenteral IV Ca therapy
- subclinical: Ca tx helps restore blood Ca concentration and promote normal fx of Ca-dependent organs
The calcium replacement needs for hypocalcemia is about:
10 grams (or about 100g total solution)
Complications of HYPERcalcemia (after giving too much IV Ca)***
- fatal cardiac complications (severe bradycardia)
- shut down PTH due to negative feedback
- if give IV Ca, give slowly
- **should never treat healthy standing cow with IV Calcium!!! Give these cows oral Ca. IV Ca will shut down PTH, and cow will have relapse of even worse hypoCa a day later.
Oral calcium compounds**
- Ca chloride and sulfate (high diffusion)
- Ca propionate (lower diffusion, but provides propionate as a glucose precursor)
- Ca carbonate (poorly absorbed)
**caution with feeding anionic diet while giving Ca chloride supplement –> can exacerbate the metabolic acidosis. Use Ca propionate instead
Bone is/is not a significant source of Mg
Is NOT
Maintenance of normal plasma Mg concentration is dependent on:**
Daily dietary Mg absorption
-absorbed in the SI of young calves and lambs, then rumen as they get older
What blood level is considered Hypomagnesia?
Blood Mg
Sequelae of hypoMg
- 2ary hypoCa
- depressed feed intake and rumen contraction
- tetany in grazing cattle
Prevention of hypoMg
Avoid grasses low in available Mg, high in K (lush spring grass)
-K inhibits Mg absorption in the rumen
Add extra Mg to diet ie. Oral Mg supplement
Correlation between Hypocalcemia and Hypophosphatemia***
- Same etiology that can cause hypocalcemia can also cause hypophosphatemia
- If there is hypocalcemia, there is high PTH, which causes P loss via saliva and urine
- Ruminal atony from hypocalcemia results in salivary P pools in the rumen that can’t be reabsorbed
- Ca tx restores normal blood P concentrations
- restoring normocalcemia halts PTH secretion, which stops P loss and increases GI motility. intestinal absorption of salivary P that had pooled in the rumen can then resume.
- Cows with low blood P (despite Ca tx) are at a greater risk for becoming alert downer cows
Prevention of hypoP
Prevent hypoCa
Diet
Tx: 6 g phosphorus IV, or correct hypoCa
Causes of hypokalemia
- prolonged Inappetence (>2 days)
- corticosteroid tx that have mineralocorticoid activity (isoflupredone acetate), which enhances renal and GI losses of K
CS of hypokalemia
- generalized muscle weakness, depression, muscle fasciculations
- severe: unable to stand or lift head
Dx of hypokalemia
Severe:
Tx of hypokalemia
Oral potassium
-KCl in feed
Rarely administered IV except when recumbent or severe
High rates of K administration can cause arrhythmias, including VPCs, ventricular fib, and death.
Macro mineral challenges in cattle
- hypocalcemia
- hypoMg
- Hypophosphatemia
- HypoK
