Negative energy balance Flashcards
What is the hormonal response during negative energy balance?
Insulin decreases Thyroxine decreases Glucagon increases Growth hormone (GH) increases Cortisol increases Catecholamines (e.g. epinephrine) increase
Why do dairy cows get a negative energy balance?
They have high energy demands due to the fetus in late gestation, demands of milk production and transient anorexia at the time or parturition.
Why do cows rely on gluconeogenesis?
Ruminants rely upon gluconeogenesis to create glucose from non-carbohydrate substrates (e.g. propionate)
What are the volatile fatty acids produced by rumen bacteria?
The Volatile fatty acids produced by fermentation:
Acetate 70%
Propionate 20%
Butyrate 10%
How are the VFA’s processed to glucose? What does this make the ratio like?
Propionate is Glucogenic and Acetate and butyrate are ketogenic so this makes the Ratio of ketogenic to glucogenic is 4:1
How are the ketogenic VFA’s processed?
Acetic acid and butyric acid cannot be converted into glucose but instead are converted to acetyl CoA which enters the TCA cycle; ATP produced and is converted into fats for storage but can also end up as ketones.
What does HSL do?
HSL liberates fatty acids and glycerol from triglycerides
Fatty acids used to produce ATP via beta oxidation within mitochondria
What switches HSL on and off?
HSL is kept switches off by high insulin but it can be turned on by high glucagon, stress catecholamines, growth hormone and cortisol.
How do cows with fatty liver present?
On physical exam the cow will have decreased rumen motility, ketoisis (characteristic odour on breath or positive urine ketone result) and may have concurrent disease (Dystocia, left displaced abomasum (LDA), retained placenta, metritis, or mastitis)
What are the risk factors for fatty liver?
Risk factors include: High body condition cows, older cows, insulin resistance (obesity induced, stress induce by epinephrine or cortisol, pregnancy progesterone induced or due to the peak in cortisol prior to parturition), concurrent disease, improper housing and poor nutrition leading to insufficient calories at the start of lactation.
How does negative energy balance cause fatty liver?
Negative energy balance stimulates the excessive release of fatty acids from adipose tissues
There is an increase in blood non-esterified fatty acid concentration
Overwhelms the capacity of the liver to use fatty acids for energy production
Fatty acids converted back into triglyceride and stored in the liver
Triglyceride accumulation within hepatocytes causes hepatic dysfunction.
How is fat mobilised in times of negative energy balance?
Fatty acids (16 carbons) hydrolyzed into two-carbon units of acetyl CoA
Energy (ATP) generated as bonds broken
End-product is acetyl CoA
Complete oxidation when acetyl CoA enters the TCA cycle by reacting with oxaloacetate
The acetyl CoA from fat needs to react with oxaloacetate to release the energy, but where does this oxaloacetate come from?
From propionate, but if the animal isn’t eating very well this doesn’t let energy be metabolized from the acetyl coA which mean the excess fatty acids need to be repackaged into triglycerides and stored in hepatocytes.
Excess Acetyl CoA can be diverted into ketones
What causes the production of ketones?
Ketones are produced from acetyl CoA
More ketones produced when there is insufficient oxaloacetate (anorexia)
Lack of propionate causes a decrease in oxaloacetate (fat cows that aren’t eating)
How do cows with ketosis present?
This will present as a cow with fruity pear drop breath, in excess the cow ill have ketoacidosis which lowers the blood pH and effects enzymatic activity, lowered appetite and leaked liver enzymes into the blood as the hepatocytes swell
