Hormones and energy metabolism

Question 1

How do hormones respond to a negative energy balance?

Answer 1

• They aim to lower the metabolic rate so the resources last longer
• Insulin decreases, thyroxine decreases, glucagon increase, GH increases, cortisol increases, catecholamines increase

Question 2

List some diseases that involve an energy metabolism disorder

Answer 2

• Hepatic lipidosis
• Secondary ketosis
• Feline hepatic lipidosis
• Equine hyperlipidaemia

Question 3

Discuss the 3 VFAs produced by fermentation in ruminants

Answer 3

1) Acetate= Ketogenic
2) Propionate= Glucogenic
3) Butyrate = Ketogenic

Question 4

How is propionate used to make glucose?

Answer 4

Proprionic acid is converted to oxaloacetate

Oxaloacetate is converted into glucose via gluconeogenesis

Question 5

What happens to acetate and butyrate?

Answer 5

They cannot be converted into glucose

instead they are converted to acetyl CoA and fed into the kerbs cycle to produce ATP

Question 6

What is the role of HSL?

Answer 6

Mobilses fatty acids and glycerol from TGs

These fatty acids are used to produce ATP via beta oxidation within mitochondria

Question 7

What inhibits HSL?

Answer 7

Insulin

Question 8

What stimulates HSL?

Answer 8

A state of negative energy

• Low insulin/ high glucagon
• Stress (catecholamines)
• GH
• Cortisol

Question 9

Discuss hepatic lipidosis in dairy cattle

Answer 9

Presents in periparturient dairy cows
-Lower milk production
-Loss of appetite
-Mild depression
Physical exam should show: Decreased rumen activity and ketosis

Question 10

What factors increase the risk of dairy cattle developing fatty liver?

Answer 10

• Obesity: animals with a higher BCS have more fat to mobilise hence more fat goes to the liver.
• Older cows
• Insulin resistance
• Poor nutrition: lack of calories at start of lactation

Question 11

Why is insulin resistance a problem in dairy cows with fatty liver?

Answer 11

• Obesity induced

- Pregnancy/ parturition increases stress (high cortisol)

Question 12

What are the periparturient events that can contribute to fatty liver in dairy cows?

Answer 12

• Neg energy balance in late pregnancy: fetus increases energy demand and the cow doesn’t eat as much at parturition
• Shift in blood hormones at parturition: insulin, IGF-1 and thyroid hormones decrease. GH, prolactin and cortisol increase

Question 13

What is the main driving force behind hepatic lipidosis?

Answer 13

-Excessive mobilisation of fatty acids: overwhelms capacity of the liver to use fatty acids for energy production-> build up of TGs in liver-> lippid vacuoles build up in cytoplasm of hepatocytes and disrupt normal function

Question 14

What must Acetyl CoA bind with to enter TCA cycle?

Answer 14

Oxaloacetate

Question 15

What impact does silage conditions have on fermentation?

Answer 15

-The wetter the conditions the more likely butyric acid will be formed

Question 16

What is the link between oxaloacetate and anorexia?

Answer 16

When the cow isn’t eating as much propionate decreases in concentration. As propionate can convert to oxaloacetate there is also reduced oxaloacetate. This makes a bottle neck in the cycle as acetate and butyrate convert to Acetyl CoA. BUT acetyl CoA cannot enter TCA cycle without oxaloacetate.

Question 17

Discuss the different problems that occur due to anorexia

Answer 17

• Lowered propionate so lowered oxaloacetate
• Bottle neck leading to excess acetyl CoA which forms ketone bodies
• Excess fatty acids which re stored as TGs in liver. Lipid vacuoles in cytoplasm of liver cells affect function.

Question 18

What are the clinical affects of ketosis?

Answer 18

• Fruity smell to breath
• Ketoacidosis
• Lowers blood pH and affects enzyme reactions
• CNS depression
• Lowers appetite= vicious cycle

Question 19

What is the TG overflow system?

Answer 19

TG’s are aloe to exit the liver as VLDLs

-Cows aren’t good at it but horses are

Question 20

What is the main risk in cats of developing hepatic lipidosis

Answer 20

Obesity and negative energy balance

-You need to get nutrition into them to try and stop the cycle

Question 21

Describe hyperlipidaemia in horses

Answer 21

• Often follows on from choke or laminitis-> go off their feed due to pain
• Very good at repackaging TGs into VLDLs.
• Results in organ dysfunction due to systemic hyperlipidaemia