L13: Hypocalcemia And Micronutrient Deficiencies (Risco)

Question 1

All cows experience hypocalcemia around calving, but only 6% develop clinical signs (milk fever)

Answer 1

25-50% of cows have sub-clinical hypocalcemia during first 12 days pp
-use of anionic diets most common cause

Question 2

What is considered hypocalcemic?

Question 3

Ionized calcium is about what percent of total calcium?

Answer 3

50% (ICa is physiologically active)

Question 4

Why does Ca drop right before parturition?

Answer 4

• 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

Question 5

What does 1-alpha hydroxylase do?***

Answer 5

Converts inactive vit. D (1,25-dihydroxyvitamin D) to active form (Calcitriol)

Question 6

Where is 1,25-dihydroxyvitamin D stored? Functions?

Answer 6

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.”

Question 7

Etiology of hypocalcemia

Answer 7

• 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

Question 8

Dietary cation anion difference ***

Answer 8

-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

Question 9

Posture, attitude, and pulse of stage 1 hypocalcemia

Answer 9

Posture: ataxic, standing, unsteady
Attitude: alert, excited
Pulse: normal, muffled

Question 10

Posture, attitude, and pulse of stage 2 hypocalcemia

Answer 10

Posture: sternal recumbency
Attitude: alert to depressed
Pulse: increased (90 bpm) and weak

Question 11

Posture, attitude, and pulse of stage 3 hypocalcemia

Answer 11

Posture: lateral recumbency w/ complete muscle flaccidity
Attitude: depressed to comatose
Pulse: rapid (>110), weak, muffled

Question 12

Milk fever = the gateway disease to:

Answer 12

• mastitis
• DAs
• metritis
• ketosis
• etc.

Question 13

Therapeutic considerations for hypoCa

Answer 13

• clinical (milk fever) requires parenteral IV Ca therapy

- subclinical: Ca tx helps restore blood Ca concentration and promote normal fx of Ca-dependent organs

Question 14

The calcium replacement needs for hypocalcemia is about:

Answer 14

10 grams (or about 100g total solution)

Question 15

Complications of HYPERcalcemia (after giving too much IV Ca)***

Answer 15

• 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.

Question 16

Oral calcium compounds**

Answer 16

• 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

Question 17

Bone is/is not a significant source of Mg

Answer 17

Is NOT

Question 18

Maintenance of normal plasma Mg concentration is dependent on:**

Answer 18

Daily dietary Mg absorption

-absorbed in the SI of young calves and lambs, then rumen as they get older

Question 19

What blood level is considered Hypomagnesia?

Answer 19

Blood Mg

Question 20

Sequelae of hypoMg

Answer 20

• 2ary hypoCa
• depressed feed intake and rumen contraction
• tetany in grazing cattle

Question 21

Prevention of hypoMg

Answer 21

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

Question 22

Correlation between Hypocalcemia and Hypophosphatemia***

Answer 22

• 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

Question 23

Prevention of hypoP

Answer 23

Prevent hypoCa
Diet
Tx: 6 g phosphorus IV, or correct hypoCa

Question 24

Causes of hypokalemia

Answer 24

• prolonged Inappetence (>2 days)
• corticosteroid tx that have mineralocorticoid activity (isoflupredone acetate), which enhances renal and GI losses of K

Question 25

CS of hypokalemia

Answer 25

• generalized muscle weakness, depression, muscle fasciculations
• severe: unable to stand or lift head

Question 26

Dx of hypokalemia

Answer 26

Severe:

Question 27

Tx of hypokalemia

Answer 27

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.

Question 28

Macro mineral challenges in cattle

Answer 28

• hypocalcemia
• hypoMg
• Hypophosphatemia
• HypoK