Lecture 3a - Nutritional peculiarities of cats

Question 1

In order from greatest to least, what are cat energy substrates?

Answer 1

protein > fats > carbohydrates

Question 2

How do cats differ from dogs in terms of natural diet, dietary amount of CHOs, amount of glucose absorbed, and time of gluconeogenesis?

Answer 2

Natural diet
- Cat: meat-based
- Dog: plant and meat-based

Dietary amount of CHOs
- Cat: small
- Dog: considerable (due to more plant based material)

Amount of glucose absorbed
- Cat: small (not many CHOs)
- Dog: considerable

Time of gluconeogenesis
- Cat: CONSTANT! Constant conversion of protein and fat into glucose. “The engine is always running”.
- Dog: Periods of low blood glucose aka in the post absorptive state. When there is no more glucose coming into the portal vein.

Question 3

What is a cat’s dietary requirement for carbohydrates?

Answer 3

NONE; cats don’t need to eat starch and fiber to survive.
- might be necessary for adequate lactation, but that is it

Question 4

Can cats efficiently use simple carbohydrates?

Answer 4

YES! If there were glucose in the lumen of the gut, the cat could make use of it.
- Lactose and galactose tolerance (aka they can have a certain amount in the diet and not get sick)

Question 5

What would be some reasons to include fibre in a cat diet?

Answer 5

• More soluble fibre to help slow down digesta flow for cats with diabetes
• Prevention of constipation by including insoluble fibre
• Useful for prebiotic activity aka feeding the microbes in the gut a fermentable fibre

Question 6

In terms of taste, what are cats attracted to and what are they not attracted to?

Answer 6

Attracted to: AA, nucleotides, salty, sour, bitter

Not attracted to: CHOs or sweeteners

Question 7

Why can’t cat’s taste “sweet”?

Answer 7

Tas1r2/Tas1r3 encode sweet taste receptors in mammals.

In cats Tas1r2 is not expressed so the taste receptor is incomplete. This is unique to cats!

Question 8

Cats have a reduced capability to digest starch, how is this reflected in carbohydrate metabolism?

Answer 8

• Pancreatic alpha-amylase activity is only 5% of those in dogs.
• Disaccharidase activity is only 40% activity of those in dogs

Question 9

Cats have a decreased expression of SGLT, why is this important?

Answer 9

Carbohydrate metabolism.
- Cat has a lower expression of the glucose transporter; both cats and dogs can uptake glucose but dog has a greater ability to uptake it from the lumen.
- still some background level of the cat being able to uptake starch despite being a carnivore

Question 10

What is glycolysis? What important enzyme do cats lack in relation to glycolysis?

Answer 10

Glycolysis = the first step of utilizing glucose as energy

• Cats have minimal glucokinase; most efficient way to turn glucose into glucose 6-phosphate
• Cats lack fructokinase; result is fructosuria = they can’t uptake fructose into tissue so it is excreted in the urine as a safety mechanism
• Cats, like every other mammal, have normal activity hexokinase which is found in all tissues

Question 11

What do cats rely on to sustain blood glucose?

Answer 11

Gluconeogenesis
- source of carbon skeleton: AA, propionate and glycerol

Question 12

What 2 AA are solely ketogenic and cannot be used for gluconeogenesis?

Answer 12

Lysine and Lucine

Question 13

Why do cats have a high maintenance requirement for protein metabolism?

Answer 13

Not due to high AA requirement for synthesis of new, extra protein.

Due to high AA turnover to support ongoing gluconeogenesis.
- high activity of hepatic enzymes
- urea cycle enzymes

Question 14

Why does the urea cycle exist?

Answer 14

This about the high maintenance requirement for protein that cats have. They use the protein for gluconeogenesis. The AA is cleaved into C-skeleton (turned into glucose) and N which is toxic and direct towards the urea cycle.

Question 15

In regards to protein metabolism, what enzyme activity can cats not decrease?

Answer 15

Hepatic enzymes, they are constantly active, supporting high AA turnover.
- fixed amount of protein catabolized for energy

Question 16

Why is the urea cycle important?

Answer 16

To get rid of the ammonia molecule of nitrogen toxicity

Question 17

What are unique adaptions to urea cycle enzymes in cats?

Answer 17

• Not adaptive to dietary protein level
• Highly efficient detoxification of nitrogen wastes
• Reduced nitrogen conservation

Question 18

What happens to the urea cycle during fasting or reduced protein intake in cats?

Answer 18

• Urea cycle intermediates deplete; particularly arginine. A lot of N waste will still be getting generated but the urea cycle will stop.
• Key intermediate: Ornithine; replenished by eating protein
• Dietary precursor: Arginine

Question 19

Cats have an arginine requirement, what happens if they consume arginine-deficient meals?

Answer 19

• Ammonia cannot be converted to urea
• Ammonia toxicity <1 hour
• Death within 2-5 hours

Question 20

What is taurine? What is it used for?

Answer 20

Beta-amino sulfonic AA (not an AA but behaves like one)
- Taurine is important for bile acid conjugation (taurine + bile acid = bile salt) = important for fat digestion
- Essential for normal retinal, cardiac, neurologic, reproductive, immune and platelet function

Question 21

What is the only AA that cats use to conjugate bile acids?

Answer 21

Taurine
- cannot change to glycine conjugation unlike other animals
- required for formation of micelles

Question 22

Why are micelles needed?

Answer 22

To absorb LCFA into the enterocyte

Question 23

What are ways to meet the taurine requirement?

Answer 23

Abundant in animal tissues, absent in plants.
- likely need to add synthetic taurine to the cat’s diet

Question 24

What are the outcomes of taurine deficiency?

Answer 24

• Feline central retinal degeneration
• Reproductive failure and impaired fetal development
• Feline dilated cardiomyopathy

Question 25

Why is methionine an important AA to be aware of for cats?

Answer 25

First limiting AA in cat diets formulated with natural ingredients

Question 26

What is methionine a precursor to?

Answer 26

cysteine
- but Cys is NOT a precursor to Met

Question 27

Why is cysteine an important AA to be aware of for cats?

Answer 27

Cysteine can provide about half of need for sulfur AA
- low in veg-based diets
- must be supplemented by synthetic/crystalline DL-methionine

Question 28

Why is feed-grade crystalline methionine available but not cysteine?

Answer 28

Bc you can add synthetic Met to diet and meet the requirements for both Met and Cys

Question 29

What are the possible explanations for why cats have a higher requirement for methionine and cysteine than other species?

Answer 29

• Cysteine synthesis
• Taurine synthesis (limited)
• High rate of met catabolism
• Hair synthesis
• Felinine (a sulfur AA) is high in adult male cats

Question 30

What is the main form of stored energy?

Answer 30

Triglycerides

Question 31

Besides a main form of stored energy, what are 4 other functions of fat?

Answer 31

1. fat soluble vitamins
2. structural cell elements
3. hormones/prostaglandins
4. insulator/protective layer

Question 32

Do cats have a high ability to digest and use fat?

Answer 32

YES

Question 33

Why do cats have a special need for arachidonic acid?

Answer 33

• Cannot synthesize it from linoleic acid due to low hepatic delta6 desaturase activity

Question 34

What are dietary sources of arachidonic acid?

Answer 34

ONLY fats from animal tissues
- related to strict carnivorous behaviour of cats

Question 35

What are 4 D’s?

Answer 35

diarrhea, dermatitis, dementia, and death

Question 36

What does a niacin deficiency result in?

Answer 36

Pellegra (4 D’s)

Question 37

Why is niacin (vitamin B3) a requirement in cat diets?

Answer 37

Due to competing metabolic pathways of tryptophan; cat cannot produce niacin from tryptophan despite possessing all the enzymes due to high activity of picolinic carboxylase

Question 38

Why do cats have a higher (4x) pyridoxine requirement (vitamin B6) than dogs?

Answer 38

• energy from aa
• high transaminase activity
• high pyridoxine turnover

Question 39

Why do cats have a vitamin A requirement?

Answer 39

Cats cannot convert beta-carotene to vitamin A because they lack the intestinal enzyme to cleave and oxidize carotenoids.

Cats require pre-formed vitamin A naturally occurring in animal tissue.

Question 40

What is the function of vitamin A, what is it typically synthesized from?

Answer 40

• Growth, development, immune system, vision
• Typically synthesized from carotenoids (beta-carotene)

Question 41

Why is vitamin D a dietary requirement for cats?

Answer 41

Cats have insufficient 7-dehydrocholestrol in their skin and therefore cannot meet metabolic need for vitamin D-photosynthesis.

Question 42

Why is vitamin D important?

Answer 42

Calcium absorption, muscle contraction, blood clotting, nerve conductance, intracellular signal induction, phosphorus homeostasis

Question 43

In comparison to a dog, what is unique about a cat’s water requirement?

Answer 43

• Ancestors’ adaptation to desert environment
• thirst stimulus = less sensitive = survive on less water than dogs
• can lose as much as 8% of their body water

Question 44

How do cats compensate for low water intake? What is the risk?

Answer 44

By highly concentrated urine
- highly saturated urine = risk of crystalluria or urolithiasis
- FLUTD

Question 45

How does feeding method affect feline urinary pH?

Answer 45

• if urinary pH becomes too low, one type of crystal forms and it it becomes too basic another form of crystal forms
• need an optimum urinary pH to prevent too many crystals from forming
• one meal a day causes an increase in pH whereas grazing doesn’t cause the spike and subsequent risk