Nutrition Flashcards
(12 cards)
How Different Animals Utilise Nutrients
Regulation of Feed Intake in the Brain
The hypothalamus arcutae nuclei contain two sets of neurons which have opposite effects on feeding behaviour. A continuous repression of the stimulus to eat is caused by CART neurons. A continuous stimulus to eat is caused by neuropeptide Y and AGRP neurons. Signals to the hypothalmus originate from the digestive tract due to wall distension and osmolarity of rumen contents, from the liver due to blood metabolite concentrations and from the pancreas due to insulin production.
Nervous Regulation of Feed Intake
Digesta in digestive tract is sensed by distension ans osmotic sensors. Information is carried to the brain by vagus nerve and by movement of ghrelin in the blood. Activation of neuropeptide Y and CART neurons in the arcuate nucleus. Neuroregulators are synthesised and move across the synaptic gap to activate nerves in the ventromedial nuclei. Information is transferred to the cortex and eating behaviour is initiated or stopped.
Taste and smell are recognised in the nucleus of the solitary tract and olfactory bulb. These have neurons which innervate the hypothalamus.
Hormonal Regulation of Feed Intake
Ghrelin is an oreigenic hormone that increases feeding. It is secreted from exocrine cells in the fundus and results in eating.
Leptin is a satiety hormone made in adipocytes and regulates body weight by affecting food intake and expenditure, metabolic partitioning and body composistion. It inhibits the NPY neurons, decresing the amouth of NPY secreted and promoting the activation of alpha MSH.
Neuropeptide Y stimulates feeding behaviour. It is a neurotransmitter synthesised by the NPY neurons in the arcuate nucleus. It is a potent intake stimulator which will overide the effects of satiety signals such as gut distension and increases after fastin, energy expenditure or helminth infestation.
Insulin has an integrating role. Increase in blood insulin results in up regulation of leptin mRNA in adipocyte leading ot increased leptin. Increased leptin reduces insulin synthesis and decreases insulin.
Nutrient Availability
Measurement of energy available and amino acids. Distinguishes between total and available nutrients. Available nutrient contents gives the concentrations of digestible or metabolisible energy, digestible protein and available minerals.
Availability of Energy
Food energy to digestible energy to metabolisable energy gives the net energy of feed. This occurs after the subtraction of the energy used in undigested food, endogenous secretions, urine and rumen gas and as food energy is digested.
Digestibility of energy = feed energy-energy of faeces divided by feed energy eaten.
Metabolisable energy is a unit of energy availability used mainly with ruminants and poultry.
Availability of Protein and Amino Acids
Protein digestibility = feed protein eaten-faecal energy excreted divided by feed protein eaten.
Digestible protein not often used to describe animal feeds but amino acid digestibiltiy used extensively. The content and availability of each essential amino acid is measured. Often we assume the feed’s total protein content is a good measure bu tthis is not the case. Retained amino acids are the available amino acids of the feed which can be digestd absorbed and retained by the body.
Amino acid availability measured by:
Ileal digestibility (feedstuff available is only protein source and nylon bag containing sample is recovered in animal’s faeces)
Slope-ratio assay
FNDB binding (tests wether lysine has irreversibly bound)
Reactive lysine
Breakdown of Dietary Components in Ruminants (Where nutrients are absorbed, breakdown of fibre, fatty acids, pyruvate and protein)
Digestive function in ruminants is characterised by the absorption of VFA and MH3 in the reticulo-rumen, absorption of amino acids, sugars, FA, minerals and vitamins in the small intestine and absorption of VFA, NH3 and water in the colon.
Pyruvate broken down to formic acid, CO2 and then methane.
Fibre carbohydrates broken down into acetate, butyrate and propionate. Hydrolysable carbohydrates produce glucose which is fermented to lactic and acetic acid.
Three fatty acids in small intestine can be converted to glycerol, then made into ATP through glycolysis.
Ruminants able to survive on diets lacking protein if given nitrogen source as microbes are able to produce protein.
Protein breakdown in rumen occurs via a series of chemical reactions performed by anumber of microbial organisms from protein to oligopeptides, dipeptides and NH3. Main source of protein by microbes in rumen.
Microbial Ecology of Rumen
Microbial environment dependent on temperature, feed supply, buffering, osmolarity.
Rumen bacteria are fibre, starch and protein digesters and acid utilisers. Produce fermentation end products such as formate, acetate, butyrate, lactate, succinate. Many species digest protein and oligopeptides to give NH3 and some use amino acids as energy sources. Protozoa ingest whole starch granules protecting them from faster bacterial digestion whih protects ruminants from grain engorgement poisoning.
Some symbioses between rumen microrganisms for example prevotella ruminicola digests protein to dipeptides which are used by other bacteria, methanogens adhere to protozoa and probably use hydrogen which diffuses from them. succinate produced by fibrobacter is an energy substrate for selenomonas which produces some of the CO2 used by fibrobacter. Organisms may even synthesise nutrients or excrete products essential for other organisms for example non-celluloytic bacteria synthesise the vitamin colbalamin which is needed by protozoa and celluolytic bacteria.
Important fungi genuses include neocallimastix, piromyces, sphaeomyces.
Problems Associated with Change from Roughage to Grain Diet
It always a good idea to introduce grains slowly because of the risk of bacterial fermentation o fundigested grain starch in GI.
Large amounts of grain may cause over-production of acid when rumen bacteria ferment large amounts of starch. Low pH leads to rumen stasis, death of rumen protozoa and osme bacterial absorption of acid into blood. Accretion of acid in urine leads to exhaustion of blood enterocytes.
Maintenance Energy Requirement and Production Requirements
Maintenance is keeping an animal at a particular body mass and condition and the nutrient requirement for maintenance are the amounts of nutrients needed for these purposes.
MER = energy for basal metabolism + energy for body temperature regulation + energy for voluntary movement
Basal metabolism involves actions such as breathing, moving and digesting. May also be defined as the heat lost by an animal during catabolism.
Energy required may be broken down into maintenance (BMR, activity and temperature regulation) and production (pregnancy, lactation and growth).
Role of Nutrition in Disease ( Metabolic disorders, biotin deficiency, obesity, grain engorgement toxicity)
A metabolic disorder is any condition which reduces productivity and is associated with some abnormality in metabolism. To be a metabolic disease it must not arise from a specific genetic defect, not be a simple dietary deficiency and not be of infective origin.
Characteristic signs of biotin deficiency include dry, rough, flaky skin on the upper surface of the feet. Plantar view may show cracking of the foot pads and papilomas.
Obesity is caused by over-nutrition with physical inactivity. Health concenrs and effects of obesity includee diabetes mellitus, hypertension, decreased immunocompetance, decreased reproductive efficiency.
Grain engorgement toxicity occurs when large amounts of grain cause over production of acid when rumen bacteria ferment large amounts of starch. Increased acid prouction overwhelms buffer capcity and shifts bacterial population toward lactic acid producers instead of volatile fatty acid producers. The acid and hyperosmolarity damage colonic mucosal barrier allowing absorption of endotoxin and other large molecules. Histamine is secreted causing permeability of capillaries.
