Nutrition Flashcards
What affects nutrient availability?
Digestibility of diet, species differences in GI tract and metabolism, nutrient interactions in diet and husbandry factors - freshness of diet, storage and spoilage
Which nutrient requirement does fibre/fat increase?
Taurine
Which mineral availability does phytate reduce?
Zinc
Why do animal eat, and what is the exception?
To fulfil energy requirements, except in RUMINANTS on high fibre diets where stomach fill is important
What is the definition of a calorie?
Energy required to heat 1g of water from 15.5 degrees C to 16.5 degrees C
How do you measure the total energy in a food?
Kilojoules obtained after total combustion in a bomb calorimeter. Not all available to animal.
What is digestible energy?
Gross (total) energy minus faecal loss of energy as undigested fibre.
What is metabolisable energy?
Digestible energy minus urinary and methane loss
What is the metabolisable energy requirement (MER)?
Energy required by an inactive animal in thermoneutral conditions including the energy required to obtain and digest food
How does MER vary within species?
The higher the MER relative to body weight, the more energy needed - eg shrew has very high MER relative to body weight so must eat continually
How is MER calculated for dogs and cats?
For dogs - 100 x body weight ^ 0.75 kcal per day
For cats - 70 x weight kcal per day (a linear approximation because weight doesn’t vary much)
What is an overview of the diet of a herbivore?
Cellulose mainly. Dietary starch and glucose minimal so gluconeogenesis important
Overview of the diet of a carnivore?
Mostly protein. Starch and glucose minimal so gluconeogenesis important
Overview of the diet of an omnivore?
Significant starch and glucose. Stored as glycogen and fat. Gluconeogenesis only in fasting.
Which bond in cellulose can mammalian enzymes not break down?
Beta-1,4-glucose
Differences between ruminant and non-ruminant herbivores?
Non-ruminant herbivores have microbial fermentation in a modified large intestine. Cellulose digestion is less efficient. BUT there is some normal digestion further up the gut first so glucose can be absorbed before microbial fermentation.
Why is some bacterial breakdown of fibre in the large intestine important in omnivores?
Butyrate from colonic bacterial fermentation provides 50% of energy needs of colonic epithelial cells - may prevent colonic cancer
What is the difference in bacteria in the colon and small intestine?
In the colon gram negative and anaerobes dominate. In the small intestine, there is fewer bacteria which is mainly aerobic with fewer gram negatives
Differences between parts of ruminant stomach?
Microbial fermentation in rumen and reticulum. No secretory glands or enzymes in rumen, reticulum or omasum. Acid pH and enzymes in the abomasum.
Problems with rumination
Loses control of diet constituents, saccharides and starch broken down so adult ruminants can’t get glucose from diet. Starch escaping fermentation isn’t used because maltase activity is low and glucose absoption is poor.
Rumen volume
40 gallons
Rumen pH
6.8
Rumen temperature
38-40 degrees C
Which vitamins do rumen bacteria need?
Biotin and other B vitamins
What kind of bacteria are in the rumen?
Gram-negative anaerobes
Which vitamins do ruminal bacteria synthesize?
Vitamin K and most vitamin B requirements
What is the function of ruminal protozoa?
Metabolise cellulose and store it as a polysaccharide like starch. Feed on bacteria so if protozoa die then bacteria numbers increase. More sensitive to pH so die earlier in ruminal acidosis.
What age are ruminal microflora present from?
14 days after inoculation from older animal
What is the process of starch or cellulose metabolism in the rumen?
Starch/cellulose to short chain fatty acids then to glucose or ketones/fat
What is the process of protein and non-protein nitrogen metabolism in the rumen?
Firstly to microbial protein and then the host digests the microbes and absorbs the amino acids
Why does a dairy cow need lots of glucose?
To make lactose
Why are lots of methane, hydrogen and short chain fatty acids produced during microbial metabolism?
Because oxidation of carbohydrates and proteins must be accompanied by a reduction so there are reduced waste products
What fraction of ruminant calorie intakes is supplied by short chain fatty acids?
2/3
What are the main short chain fatty acids in microbial metabolism?
Acetate, propionate, butyrate and some valerate and isovalerate.
What is propionate used for?
Into liver and muscles to make glucose
Why do ruminants use glucose not fatty acids?
For nutrition of cells with no mitochondria or lacking oxygen supply, can’t use ketone bodies in brain, need lactose and glycerol for milk triglycerides, can be stored as glycogen, source of fructose for sperm, used for TCA cycle intermediates
What percentage of total body glucose is used for milk production at peak lactation?
85%
For the first how many weeks of lactation is there a negative energy balance?
Six
Which short chain fatty acid are used to make glucose?
Propionate and gluconeogenic amino acids
What is the fate of acetate and butyrate in a ruminant?
Converted to acetyl CoA and oxidised to make ketone bodies or fatty acids (ketogenic or lipogenic BUT NOT gluconeogenic)
What percentage of its glucose does a sheep get from propionate? And what percentage from gluconeogenic amino acids? Lactate? Glycerol?
40% and 35%, 15%, 10%
In a fasting ruminant what happens to propionate and where does the animal get the extra glucose from?
Propionate production decreases and more glucose is gained from glycerol and amino acids
Which factors affect nutrients intake?
Amount of diet fed and the availability of nutrients in the diet
Proportion of propionate converted to lactate during passage through ruminal wall
1/5
When is hepatic gluconeogenesis maximal in ruminants? How is this different in man and dogs?
After a meal when most propionate reaches the liver in the portal blood. Gluconeogenesis reduced after a meal in man and dogs due to increased insulin which inhibits gluconeogenesis.
What stimulates insulin release in ruminants?
Propionate, butyrate, isovalerate and valerate
Why is it better for less glucose to be derived from gluconeogenic amino acids in ruminants?
Important for making structural body proteins
How does increased roughage (cellulose) affect acetate and propionate?
Increased acetate, decreased propionate
How does increased concentrates affect propionate, butyrate and acetate levels?
Increased propionate and butyrate, decreased acetate
How does heating/cooking the ration affect propionate production?
Increases it
What percentages acetate, propionate and butyrate does the average dairy cow produce?
60-70, 15-20, 10-15
How is lactic acidosis caused?
Too much concentrate feed, increased lactic acid production, drop in pH, buffering capacity exceeded, desirable microflora inhibited and protozoa die so lactate producer grow favoured.
Effects of lactic acidosis
Damage to rumen wall causing bacterial infection, bacteraemia, liver abscesses, general acidosis of blood, water pulled into rumen by osmosis so hypovolaemia (reduced circulating volume), death
Which form of lactate accumulates during lactic acidosis
D forms as metabolised much more slowly than L
Why isn’t propionate fed directly to high yielding dairy cows?
Would inhibit propionate-producing microbes in rumen favouring acetate and butyrate producers causing severe propionate shortage if cow goes off food, stimulates insulin release which suppresses fatty acid release so milk fat concentration lowered, depresses appetite, unpalatable
What is the fate of triglycerides, phospholipids and cholesterol esters in the rumen?
Hydrolysed to glycerol and galactose which are fermented to short-chain fatty acids
What are the main lipogenic short chain fatty acids generated by microbial fermentation and which is the most important?
Acetate and butyrate, acetate is the most important
What do ruminal microflora do to dietary unsaturated fatty acids?
Hydrogenate them to saturated fatty acids
How does a high dietary content of unsaturated fatty acids affect microflora?
Depresses them
How does increased dietary fat affect propionate production?
Increases it
Where does most fatty acid and triacylglycerol synthesis occur in the non-lactating ruminant? What about a lactating ruminant?
Adipose tissue and mammary gland when lactating
What is the main source of absorbable amino acids for a ruminant?
Microbial protein from digestion of microbes further down the gut
How much protein does host ruminant “make” per 100g ingested organic matter?
12g
How do ruminants use non-protein nitrogen
Microbial ureases break it down to ammonia, then used to make microbial protein
Why don’t ruminants have any dietary requirement for essential amino acids?
All made by microflora as long as building blocks eg sulphur provided in diet
Why do high-yielding dairy cows require essential amino acids?
Their demand for amino acids is so high
What is the fate of most dietary nitrogen in ruminants?
Degraded by microbes by hydrolysis and deamination producing ammonia and carbon skeletons
What happens if energy is surplus in the rumen?
Microbial growth not limited, microbial cell growth increases with ruminal ammonia concentration
Which ammonia concentrations are dangerous to the host?
Above 4.5mmol/l
What happens the rumen ammonia concentration if carbohydrate or another essential component is lacking from the diet?
Ammonia concentration will rise
What percentage of ammonia produced in the rumen is incorporated into microbial protein?
90%
How is ammonia “recycled” in ruminants?
Ammonia absorbed into blood and converted to urea, urea either diffuses back in or is secreted into saliva. Then ureases break it back down to ammonia.
How is recycling of ammonia in ruminants useful?
Can metabolise more bicarbonate via CO2 which is helpful for acid-base balance as they have an excess of bicarbonate.
Why do ruminants have an excess of bicarbonate?
Plants contains lots of organic acids metabolised to bicarbonate.
What is an “escape protein” or “rumen undegradable protein”
Less soluble in rumen and resistant to microbial degradation. Pass unchanged to small intestine where they are digested similarly to man and dogs
Where are the enzymes most important for protein digestion in the small intestine produced?
Pancreas
In which area of the intestine does highest amino acid uptake occur in cows, and why is this further down than in dogs and man?
Mid to lower ileum because acid abomasal digesta is neutralised slowly and pancreatic enzymes are neutralised slowly
What % of dietary protein is nitrogen and what % is non-protein nitrogen?
85% true protein, 15% non-protein nitrogen
What % of dietary nitrogen is recycled into the rumen?
12%
What % of dietary protein is escape protein?
40%
What % of dietary non-protein nitrogen and recycled nitrogen is degraded by microbes?
100%
What % of amino acids available for absorption in the small intestine come from microbial nitrogen?
60-80%
What % of amino acids used to make milk proteins come from microbes?
65%
What % of microbial nitrogen is true protein usable by the host?
80%
What % of microbial true protein is digested and absorbed in host’s small intestine?
80%
What happens if an essential amino acid is missing from the escape proteins in the ruminant diet?
The others aren’t stored and are simply deaminated or broken down until the missing one is eaten
What percentage escape proteins are there in casein, barley, soybean meal, corn, brewer’s grains and fish meal?
10,20,30,40,50,60
How does increasing quantity of escape proteins affect wool growth, body growth and milk production?
Increases
What are the essential amino acids for ruminants?
Methionine, lysine, valine, isoleucine, leucine, histidine, threonine, phenylalanine, tryptophan and arginine
Why are lysine and methionine particularly important for ruminants?
Levels usually low in plants and lack is rate-limiting for growth and milk production
How does feeding escape proteins allow non-protein nitrogen to be included in the diet without risking ammonia toxicity?
Not degraded by ruminal microbes so aren’t a source of ammonia
Which cheap nitrogen sources in the ruminant diet can result in ammonia toxicity?
Highly degradable protein with little escape protein eg casein, large amounts of non-protein nitrogen eg urea, ammonia itself eg ammoniated molasses
Why does excess ammonia cause neurological signs?
Readily crosses blood-brain barrier and brain has no cycle to detoxify it
Why does urea cause blood alkalosis?
Binds H+ ions
How does alkalosis cause tetany?
Increased calcium binding to plasma proteins so reducing plasma ionised calcium
What is the most abundant constituent of all mammalian milks?
Water
Which lipids do ruminant milks contain?
Triacylglycerol, diglyceride, cholesterol, free fatty acids, phospholipids, monoglycerides
How does the lipid content of non-ruminant milk compare to ruminants?
Increased sterols and sterol esters, reduced triacylglycerols
How many carbons do most fatty acids in ruminant milk have?
16-18
How many carbons in the fatty acids of herbivores are more common than other animals?
4-14
At least how many different fatty acids are there in cow’s milk?
437
What is the major protein constituent of milk?
Caseins
What pH range does casein have low solubility at?
4-5
What are the amino acid components of casein?
Serine-bound phosphate, high proline content, few or no cysteines,
How are caseins present as an important source of minerals in the milk?
Micellar complexes with calcium and inorganic phosphates?
Why is low cysteine in casein not a problem?
Can be synthesised from methionine, high concentration in whey proteins
What are non-casein proteins in milk called?
Wheys
Which kinds of species have many whey proteins and which have few?
Carnivores many, rodents few
In cows which whey proteins are present?
Beta-lactoglobulin, alpha-lactalbumin, protease-peptones, traces of serum albumin and immumoglobulins
What is the predominant carbohydrate in most milks?
Lactose
Which monosaccharides make up lactose?
Glucose and galactose
Which salts are found in milk?
Sodium, potassium, calcium, magnesium, phosphate, chloride, citrate
Which is the only hormone rabbits need to maintain milk production?
Prolactin
Which hormones do cows sheep and goats need to maintain milk production?
Prolactin, growth hormone, thyroxine, parathyroid hormone, corticosteroids and oxytocin
When do lipid synthesis and lactose synthesis for milk commence?
Lipid synthesis before lactation, lactose synthesis at parturition
Where are fatty acids for milk extracted/produced?
Either extracted from blood or made from acetate and malonyl CoA
What can be the primer molecule in milk fatty acid production instead of acetyl CoA in cows?
Butyryl CoA or propionate
What % of nitrogenous compounds in milk are synthesised de novo in the mammary gland from amino acids in the blood?
92%
How is there net conversion of essential to non-essential amino acids in secretory cells for milk protein synthesis?
Mammary gland selectively takes up too many essential amino acids and too few non-essential
What is the mammary gland the only source of?
Lactose
What is the pathway of lactose production in the mammary gland?
Glucose to UDP-galactose in the cytoplasm and then UDP-galactose and glucose to lactose in the golgi by lactose synthetase
What proportion of the total substrates taken up by the bovine mammary gland is glucose?
400g/kg
What is glucose used to make in the bovine mammary gland?
Lactose and glycerol
What % of total body glucose usage does the mammary gland account for at peak lactation?
85%
What are the consequences of glucose shortage during lactation?
Body fat mobilisation to supply glycerol for gluconeogenesis and also fatty acids which can’t be used to make glucose
What happens to the fatty acids mobilised during glucose shortage during lactation?
Diverted to liver, either stored or converted to ketone bodies
What are the problems with fatty acid storage or conversion to ketone bodies during glucose shortage during lactation?
Fatty liver syndrome, ketoacidosis
What are the signs of ketosis?
Depression, loss of appetite, fall in milk yield, neurological signs and death
Why can ketosis result in death?
Ruminant brain poorly adapted to using them for energy
How is pregnancy toxaemia in ewes different to ketosis in cows?
Occurs in late pregnancy when ewe is under greatest energy and glucose demand but food supply is least (late winter)
What is the equine equivalent of pregnancy toxaemia and ketosis and how is it different?
Hyperlipidaemia - last third of pregnancy or lactation, don’t become ketotic but have elevated blood triglycerides
Why kind of pony is hyperlipidaemia most frequent in?
Shetland
What is the feline equivalent of equine hyperlipidaemia?
Hyperlipaemia
Which ketone body is not a ketone?
Hydroxybutyrate
How do ketone bodies have an advantage over long chain fatty acids as a fuel?
Don’t need albumin for transport, easily cross membranes, can be carried in higher concentrations in blood and interstitium
Which vital muscles can use ketone bodies during starvation?
Heart, diaphragm, gut and myometrium
Which dietary deficiency causes dam or kitten coat to change from black to brown?
Tyrosine or phenylalanine
Do foods for older dogs have higher or lower energy content?
Reduced
Why do large breed dogs fed fish and rice often lose weight?
Low dietary fat
Which animals need and don’t need vitamin C?
Dogs and cats don’t, guinea pigs, bats, birds and fish do
What is the intermediate between glucose and L-ascorbate?
Glucuronate
What are some functions of vitamin C?
Collagen synthesis, bile acid formation, enhances absorption of iron from gut, antioxidant
How does hepatic rate of vitamin C synthesis in dogs and cats compare to other animals?
Half
Why might you supplement vitamin C in very stressed dogs?
Vitamin C concentration decreases in stress
Where do cats obtain glucose?
Gluconeogenesis from protein
What is the % protein requirements of dogs and cats?
Cats 20-30% and dogs 18%
How does the activity of hepatic nitrogen catabolising enzymes in cats compare to the activity in dogs?
Increased activity
Why do cats go into negative nitrogen balance during insufficient protein intake? What is a consequence?
Can’t down-regulate enzymes, will break down body protein
Why have cats lost the ability to down-regulate enzymes?
Lack of selection pressure, diet always contains lots of protein
Which nitrogen catabolising enzyme activity is increased in cats compared to dogs and rats?
Alanine aminotransferase and glutamate dehydrogenase
Which amino acid can be used an a precursor in cats during an alternative hepatic gluconeogenic pathway?
Serine
Which amino acid requirement is higher in cats than man or dogs?
Arginine
How long can rats survive in nitrogen balance without arginine?
A short period
What is the pathway if arginine in the urea cycle?
Arginie to citrulline to ornithine to arginosuccinic acid to arginine
Why do cats fed arginine-free diets show signs of increased blood ammonia?
Depletion of urea cycle intermediates - can break down protein but not excrete urea
Why two enzymes involved in ornithine synthesis in cats have low activity?
Pyrroline-5-carboxylate synthase and ornithine aminotransferase
What are some possible reasons for increase cysteine and methionine requirement in cats?
Sulphur-containing amino acid called felinine excreted in urine, may be a sink for cholesterol (proved wrong) so maybe needed to make keratin for fur
What % amino acids absorbed by cats are used to make fur?
30%
Which amino acid is taurine made from?
Cysteine
What can taurine deficiency cause?
Poor reproductive performance, poor growth, dilated cardiomyopathy, retinal degeneration
How much taurine is needed to prevent retinal degeneration in cats?
500mg/kg taurine
How much taurine is needed to prevent dilated cardiomyopathy in cats?
1000-1500mg/kg in dried food and 2200-2500mg/kg in canned food
Why do cats have high taurine requirement?
Reduced ability to synthesise it from cysteine, conjugation of bile acids solely with taurine
Why do cats have reduced ability to synthesise taurine?
Low activity of cysteine dioxygenase and cysteinesulphinate decarboxylase
Which amino acids do cats, humans, rabbits and rats use to conjugate bile acids?
Cats taurine, humans taurine and glycine, rabbits glycine, rats taurine but can switch to glyco-conjugation if it’s limiting
Why is there a constant drain on taurine in cats?
Conjugation and bile acids and subsequent loss from intestines, any excess excreted in urine
Why are there different taurine requirements in dry and canned food?
Canned diets have higher fibre so more bacteria growth which split taurine from bile acids, also higher fat content stimulates bile secretion
What are the functions of taurine?
Regulates calcium flux across membranes, osmoregulation, neuromodulation
How does cow’s milk compare to meat or cats milk as a taurine source?
300x less
Why shouldn’t cats drink milk?
Undigested lactose causes osmotic diarrhoea
Why dietary requirement do cats share with mosquitos and turbot fish?
Need arachidonic acid
What are the functions of essential fatty acids?
Prostaglandin and leukotriene synthesis, maintenance of skin and coat condition and membrane function
What are signs of essential fatty acid deficiency in cats?
Hair loss, poor wound healing, anaemia and reduced fertility
Why is linoleic acid an essential fatty acid?
Mammals can’t add another double bond on the methyl side of oleic acid
How is linoleic acid converted to arachidonic acid in dogs and man?
Linoleic acid to alpha-linoleic acid to dihomo-alpha-linoleic acid to arachidonic acid
How are retinol and retinal formed?
Retinol preformed in foods of animal origin or in bacteria, retinal made from beta-carotenes in intestinal mucosa
What is beta-carotene with respect to retinal?
Two molecules of retinal joined at aldehyde end
Why enzyme can dogs and man use to convert beta-carotene to retinaldehyde?
Beta-carotene-dioxygenase
Why do cats need preformed vitamin A, not just beta-carotene?
Don’t have beta-carotene dioxygenase
What is vitamin A used for?
To make visual pigment, rhodopsin, for skin and bone development, immunity and reproduction
What is a cause and problem of vitamin A toxicity in cats?
Too much liver or cod liver oil causes hypervitaminosis A causing cartilage calcification between neck vertebrae
What is nicotinic acid important for?
Metabolic pathways for hydrogen transfer ie NAD and NADP.
In man and dogs, what is nicotinic acid formed from?
Tryptophan
In man and dogs, what % of tryotophan in converted to nicotinic acid?
1%
How does the nicotinic acid requirement of cats compare the that of dogs? Why?
4 x higher in cats because they have high activity of picolinic carboxylase so lots of glutamate and no nicotinic acid to protect against toxic effects of high tryptophan
What does deficiency of nicotinic acid cause?
Pellagra - severe mucosal and intestinal ulceration causing dehydration and death
What are some signs that cats are less able to cope with high carbohydrates?
Glucokinase activity low in feline liver, pancreatic amylase has 3x less activity than dogs, intestinal amylase stimulated less by dietary starch, cats fed high protein can maintain blood glucose level better when starved than if they’d been fed high carbs
What are signs of cobalt deficiency?
Progressive loss of appetite, weight and production, anaemia, weakness and pica - can’t make B vitamins