5: Nutritional peculiarities of cats Flashcards
Two main ways cats get energy/glucose
- Gluconeogenesis (protein -> glucose)
- Glycogen in tissues (liver/muscle)
Most important cat energy substrate?
Protein
then fat then CHOs
Time of gluconeogensis in cat vs dog
Dog = low after a meal. Postabsorptive gluconeogensis (when digesta cleared from tract)
Cat = always. Some increase after a meal
CHO dietary requirements in cats
No dietary requirement for CHOs
What kind of CHOs can cats use?
Can efficiently use simple CHOs
- sugar digestibility >94%
- no known optimal starch inclusion
- requirement for fibre
What would be some reasons to include fibre in a cats diet?
Satiety, bulking effect, prevent constipation (insoluble fibre), fermentable/soluble fibre as prebiotic (feed the microbes in the gut lumen)
Are cats attracted to sweeteners? Why?
Tas1r2/Tas1r3 are genes that encode sweet taste receptors in mammals
Tas1r2 is not expressed in cats
Cats are not attracted to sweetness/sugars
How does pancreatic a-amylase and disaccharidase activity differ in cats? What does this mean
Pancreatic a-amylase = 5% of those in dogs
Disaccharidase activity only 40% activity of those in dogs
Has limited ability to digest starch; starch must be processed with heat to open it up
What glycolysis enzymes is active in the cat? Which is not active?
Hexokinase is active in the cat (converts smaller quantities of glucose from blood stream into glucose-6-phosphate)
Glucokinase is not active (converts large quantities of glucose into glucose-6-phosphate)
Hexokinase, glucokinase and fructokinase activity in the cat? What does this mean
Hexokinase has normal activity in tissues
Glucokinase has minimal activity in liver (low glucose clearance)
Lack fructokinase (fructose -> fructose-1-phosphate): fructosuria
Cat is not well set up to handle large quantities of glucose in the blood stream
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What do cats rely on to sustain blood glucose? What provide the carbon skeleton?
Gluconeogenesis
Source of carbon skeleton: AA, propionate and glycerol
Which aa do not contribute to gluconeogensis?
Lysine and lucine (ketogenic)
How is protein metabolism unique in cats? Why?
High maintenance requirement (2x higher than adult dog)
Due to high amino acid turnover (protein degradation/synthesis)
- high activity/lack of regulation of hepatic enzymes
- urea cycle enzymes
Why does the urea cycle exist/why is it important
Need to get rid of excess N accumulating in liver from protein deamination
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LOok
How is hepatic enzyme activity unique in cats? Why?
- cannot decrease activity
- hepatic enzymes constantly active
- fixed amount of protein catabolized for energy
No evolutionary pressure to low protein diets (strict adherence to animal tissue)
What is an important reaction in the urea cycle?
Arginine to ornithine (releases urea)
What happens in the urea cycle without ornithine or arginine
No formation of urea so ammonia cannot be removed from body
With protein diet, arginine is always present so it will be able to form ornithine (low protein diet may lack arginine)
What happens to the urea cycle during fasting or reduced protein intake
- intermediates (ornithine) deplete
- with protein meal, intermediates replenish
- key intermediate: ornithine
- dietary precursor: arginine
Describe the urea cycle enzymes (adaptivity, role)
- not adaptive to dietary protein levels
- highly efficient detoxification of nitrogen wastes
- reduced nitrogen conservation
Describe the cat arginine requirement? What happens in arginine-deficiency?
Cats have an arginine requirement. They have low activity of essential enzymes in SI that produce arginine from ornithine and citrulline
Arginine-deficiency:
- ammonia cannot be converted to urea
- ammonia toxicity <1 h
- death within 2-5 hours
Name the enzymes in the SI that produce arginine from ornithine and citrulline
Pyrroline-5-carboxylate synthase and ornithine aminotransferase
What is taurine? What is it essential for
B-amino sulfonic amino acid
Role in bile acid conjugation (forming bile salts): humans and dogs can use glycine and can produce taurine
Essential for normal retinal, cardiac, neurological, reproductive, immune and platelet function
Can cats synthesize taurine?
They have limited capacity
Rate-limiting enzymes responsible for conversion of methionine and cysteine to taurine
Obligate taurine loss
Describe bile acid conjugation in cats. How do bile salts get from the intestine to the liver
Cats only conjugate bile acids with taurine (cannot change to glycine conjugation)
Conjugation required for formation of micelles
Enterohepatic circulation
What is deconjugation of bile acids
Microbial degradation
* intestinal uptake
* fecal excretion
* degradation
Taurine not produced?
What are ways to meet the taurine requirement in cats?
Animal based tissues or adding synthetic taurine to kibble
Taurine is absent in plants
Consequences of taurine deficiency in cats
- feline central retinal degeneration
- reproductive failure and impaired fetal development
- feline dilated cardiomyopathy
- hearing loss, impaired immune function
Importance of methionine? Cysteine
Met = first limiting aa in cat diets formulated with natural ingredients
Cys = can provide about half of need for sulfur AA
Role of methionine? Cysteine? What is the relationship between them in terms of conversion
Methionine = methyl group donor, coenzyme, protein, precursor to cysteine
Cysteine = glutathione precursor, felinine precursor
Met can be converted to cys but cys cannot be converted into met
Why do cats have higher met and cys requirements than other species
- cysteine synthesis
- taurine synthesis (limited)
- high rate of methionine catabolism (used as E source)
- hair synthesis
- felinine: branched-chain, sulfur aa (pheromone precursor high in adult male cats; territorial marking)
Main form of stored energy? Describe major fat depots
Triglycerides
- subcutaneous, visceral, and intestinal membranes
- extensive blood and nerve supply
- in constant state of flux
Other functions of fat
- fat soluble vitamins
- structural cell elements
- hormones/prostaglandins
- insulator/protective layer
Slide 31
Fat metabolism
What f.a. requirement is unique in cats? Why do they have this
Arachidonic acid
Linoleic acid cannot be converted to AAc in sufficient amounts
Why does the LA to AAc pathway not run in sufficient amounts
Low hepatic (triangle)6 desaturase activity
- rate-limiting factor in conversion of linoleic acid to y-linolenic acid which is elongated to AAc
Dietary source of arachidonic acid
Only fats from animal tissues (strict carnivorous behaviour in cats)
Deficiency in niacin causes…
Pellegra (4 D’s) = diarrhea, dermatitis, dementia and death
Why is there a niacin requirement in cats?
Tryptophan is metabolized to niacin, but there are competing metabolic pathways
They possess the enzymes, but the pathway from tryptophan to acetyl CoA is running at very high speeds (high activity of picolinic carboxylase), so most tryptophan is not available for conversion into niacin (must add to diet)
Source of niacin?
Animal tissue is high in niacin
Describe the cat pyridoxine requirement
Higher than dogs (4x)
- energy from aa
- high transaminase activity
- high pyridoxine turnover
Function of vitamin A? Synthesis
- growth, development, immune system, vision
- typically synthesized from carotenoids (B-carotene)
Cat requirement for vitamin A/retinol
- cannot convert B-carotene to vitamin A (lack intestinal enzymes to cleave and oxidize) (dogs can)
- cats require pre-formed vitamin A (naturally occurring in animal tissues (fats)
Function of vitamin D
calcium absorption, muscle contraction, blood clotting, nerve conductance, intracellular signal induction, P homeostasis
Cat requirement for vitamin D
- dietary requirement
- have insufficient 7-dehydrocholesterol in their skin (cannot meet metabolic need for vitamin D-photosynthesis (cannot use sunlight to produce))
- found in animal tissues/fat
How is cat water requirement different than dogs? What allows them to do this?
- thirst stimulus = less sensitive (survive on less water than dogs; ignore minor levels of dehydration (up to 4% BW))
- compensate low water intake by highly concentrated urine
What is the risk of highly concentrated urine in cats
Highly saturated urine = risk of crystalluria or urolithiasis
- feline lower urinary tract disease complex
Cats can lose as much as ____ of their body water
8%
Name nutrients that are required to be in the diet
- arachidonic acid
- arginine
- taurine
- niacin (B3)
- vitamin A/retinol
- vitamin D
