Lecture 3a - Nutritional peculiarities of cats Flashcards
In order from greatest to least, what are cat energy substrates?
protein > fats > carbohydrates
How do cats differ from dogs in terms of natural diet, dietary amount of CHOs, amount of glucose absorbed, and time of gluconeogenesis?
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.
What is a cat’s dietary requirement for carbohydrates?
NONE; cats don’t need to eat starch and fiber to survive.
- might be necessary for adequate lactation, but that is it
Can cats efficiently use simple carbohydrates?
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)
What would be some reasons to include fibre in a cat diet?
- 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
In terms of taste, what are cats attracted to and what are they not attracted to?
Attracted to: AA, nucleotides, salty, sour, bitter
Not attracted to: CHOs or sweeteners
Why can’t cat’s taste “sweet”?
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!
Cats have a reduced capability to digest starch, how is this reflected in carbohydrate metabolism?
- Pancreatic alpha-amylase activity is only 5% of those in dogs.
- Disaccharidase activity is only 40% activity of those in dogs
Cats have a decreased expression of SGLT, why is this important?
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
What is glycolysis? What important enzyme do cats lack in relation to glycolysis?
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
What do cats rely on to sustain blood glucose?
Gluconeogenesis
- source of carbon skeleton: AA, propionate and glycerol
What 2 AA are solely ketogenic and cannot be used for gluconeogenesis?
Lysine and Lucine
Why do cats have a high maintenance requirement for protein metabolism?
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
Why does the urea cycle exist?
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.
In regards to protein metabolism, what enzyme activity can cats not decrease?
Hepatic enzymes, they are constantly active, supporting high AA turnover.
- fixed amount of protein catabolized for energy
Why is the urea cycle important?
To get rid of the ammonia molecule of nitrogen toxicity
What are unique adaptions to urea cycle enzymes in cats?
- Not adaptive to dietary protein level
- Highly efficient detoxification of nitrogen wastes
- Reduced nitrogen conservation
What happens to the urea cycle during fasting or reduced protein intake in cats?
- 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
Cats have an arginine requirement, what happens if they consume arginine-deficient meals?
- Ammonia cannot be converted to urea
- Ammonia toxicity <1 hour
- Death within 2-5 hours
What is taurine? What is it used for?
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
What is the only AA that cats use to conjugate bile acids?
Taurine
- cannot change to glycine conjugation unlike other animals
- required for formation of micelles
Why are micelles needed?
To absorb LCFA into the enterocyte
What are ways to meet the taurine requirement?
Abundant in animal tissues, absent in plants.
- likely need to add synthetic taurine to the cat’s diet
What are the outcomes of taurine deficiency?
- Feline central retinal degeneration
- Reproductive failure and impaired fetal development
- Feline dilated cardiomyopathy
Why is methionine an important AA to be aware of for cats?
First limiting AA in cat diets formulated with natural ingredients
What is methionine a precursor to?
cysteine
- but Cys is NOT a precursor to Met
Why is cysteine an important AA to be aware of for cats?
Cysteine can provide about half of need for sulfur AA
- low in veg-based diets
- must be supplemented by synthetic/crystalline DL-methionine
Why is feed-grade crystalline methionine available but not cysteine?
Bc you can add synthetic Met to diet and meet the requirements for both Met and Cys
What are the possible explanations for why cats have a higher requirement for methionine and cysteine than other species?
- Cysteine synthesis
- Taurine synthesis (limited)
- High rate of met catabolism
- Hair synthesis
- Felinine (a sulfur AA) is high in adult male cats
What is the main form of stored energy?
Triglycerides
Besides a main form of stored energy, what are 4 other functions of fat?
- fat soluble vitamins
- structural cell elements
- hormones/prostaglandins
- insulator/protective layer
Do cats have a high ability to digest and use fat?
YES
Why do cats have a special need for arachidonic acid?
- Cannot synthesize it from linoleic acid due to low hepatic delta6 desaturase activity
What are dietary sources of arachidonic acid?
ONLY fats from animal tissues
- related to strict carnivorous behaviour of cats
What are 4 D’s?
diarrhea, dermatitis, dementia, and death
What does a niacin deficiency result in?
Pellegra (4 D’s)
Why is niacin (vitamin B3) a requirement in cat diets?
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
Why do cats have a higher (4x) pyridoxine requirement (vitamin B6) than dogs?
- energy from aa
- high transaminase activity
- high pyridoxine turnover
Why do cats have a vitamin A requirement?
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.
What is the function of vitamin A, what is it typically synthesized from?
- Growth, development, immune system, vision
- Typically synthesized from carotenoids (beta-carotene)
Why is vitamin D a dietary requirement for cats?
Cats have insufficient 7-dehydrocholestrol in their skin and therefore cannot meet metabolic need for vitamin D-photosynthesis.
Why is vitamin D important?
Calcium absorption, muscle contraction, blood clotting, nerve conductance, intracellular signal induction, phosphorus homeostasis
In comparison to a dog, what is unique about a cat’s water requirement?
- 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
How do cats compensate for low water intake? What is the risk?
By highly concentrated urine
- highly saturated urine = risk of crystalluria or urolithiasis
- FLUTD
How does feeding method affect feline urinary pH?
- 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
