3: homeostasis and metabolic challenges

Question 1

what is homeostasis?

Answer 1

regulation of a stable internal environment
- constant challenge of change
- maintaining functions within tolerable limits
- adjustments made by by negative feedback

Question 2

explain how a negative feedback loop works

Answer 2

change detected by body sensors + controlled by brain. adjustments through effectors: endocrine system (hormones) and nervous system (nerve cells + signals)

Question 3

what is an inherited homeostatic imbalance/failure?

Answer 3

diabetes

Question 4

what percentage of the body’s calcium is in the bones?

Answer 4

99%

Question 5

what is the normal mass of calcium in blood?

Answer 5

8-12g

Question 6

how are calcium levels in blood regulated (if not by diet)?

Answer 6

• kidney filtration and reabsorption
• bone formation and resorption (via osteoclasts)

Question 7

what happens if the blood Ca level is low?

Answer 7

1. Parathyroid hormone stimulated
2. Cholecalciferol in liver activated
3. Hydroxycholecalciferol is formed
4. activated in kidneys to dihydroxycalciferol
5. Ca - binding protein synthesized: acts on gut, kidneys and bones to raise blood Ca

Question 8

what is milk fever?

Answer 8

hypocalcaemia: low blood Ca

Question 9

what percentage of dairy herds have milk fever?

Answer 9

5-8%

Question 10

how much calcium does a dry cow need per day?

Answer 10

15g

Question 11

how much calcium does a cow in early lactation need per day?

Answer 11

50-60g

Question 12

what measures can be taken to prevent milk fever?

Answer 12

• calcium infusion + vit D when calving, low Ca diet when dry
• diet balanced for cations and anions

Question 13

what percentage of Mg is found in bones?

Answer 13

70%

Question 14

what is dissolved Mg needed for?

Answer 14

enzyme activity for carbohydrate + lipid metabolism

Question 15

what symptoms arise from Mg deficiency?

Answer 15

nervous irritability, convulsions, hypomagnesaemic tetany

Question 16

what are high vs low Mg foods?

Answer 16

high in vegetable protien feeds
low in rapidly growing grass

Question 17

What are the grass staggers?

Answer 17

hypomagnesaemic tetany

Question 18

in what season is there a higher risk of grass staggers?

Answer 18

spring/autumn

Question 19

what is Mg absorption affected by?

Answer 19

K (potassium), protein, low fibre

Question 20

how much Mg do cows need per day?

Answer 20

20-30g

Question 21

how much Mg do ewes need per day?

Answer 21

2-3g

Question 22

what is hyperlipaemia (fatty liver) induced by?

Answer 22

increased energy requirements coinciding with reduced energy intake

Question 23

when are dairy cows most susceptible to hyperliaemia?

Answer 23

at calving

Question 24

when are alpacas and llamas most susceptible to hyperliaemia?

Answer 24

in late preganancy

Question 25

when are ponies and donkeys most susceptible to hyperlipaemia?

Answer 25

during pregnancy + lactation

Question 26

what is hyperlipaemia?

Answer 26

fatty liver

Question 27

what is urolithiasis?

Answer 27

stones in kidney and bladder

Question 28

what are salt precipitates that form crystals in kidney/bladder made of?

Answer 28

usually Mg, NH4, also Ca oxalate

Question 29

which animals are most susceptible to urolithiasis?

Answer 29

dogs, cattle, sheep

Question 30

what can happen to animals with urolithiasis?

Answer 30

bladder ruptures

Question 31

what are predisposing factors (risk factors) for urolithiasis?

Answer 31

- males - diet with high levels of P + Mg, excess - infection - alkaline urine

Question 32

what are changes that can be observed in animals with urolithiasis?

Answer 32

- wide leg posture to relieve pain - straining when passing urine - small volumes of blood stained urine - crystals around penis

Question 33

how do you prevent urolithiasis?

Answer 33

- suitable and balanced diet (Ca supplementation: Ca:P 2-2.5:1) - minimise Mg and P in diet - risk reduced by low pH urine -> add 0.5-1% NH4Cl - maximise urine volume: add 1.4% salt - avoid breeding from recurrent cases