Measuring Nutritional Value & Food Consumption

Flashcards from lecture notes on Measuring Nutritional Value & Food Consumption

Food Intake

Animal attempts to balance needs with resources in part through intake. Intake rate is as important as food quality. Influenced by internal & external processes. A key measure of factors

External Influences on Food Intake (Short Time Scale)

Early research considered intake rate a function of searching and handling time. Intake increases with increasing density up to an asymptote. Works for predators.

Herbivore Food Intake

Early attempts to predict intake rate for herbivores based on plant biomass. Intake more closely related to bite size in many situations.

Models to Predict Herbivore Intake Rate

Plant Density, Plant Apparency, Bite Density, Travel Velocity, Search Width, Bite Size

Internal Influences on Intake Rate

Size of a meal, How often an animal feeds, Food quality

Physical Regulation of Food Intake

Distention, Physical capacity, Rate at which food clears the digestive tract, Digestion and absorption

Physical Regulation Passage Rate

In ruminant, passage rate determined by Particle size – rumination rate and fiber content. Grinding feeds will increase passage. Flexibility in passage of food out of the rumen.

Physiologic Regulation on Food Intake

Many mechanisms tied to energy status. Neuropeptides and neurotransmitters, Hormones, GI-tract peptides, Nutrients, Ammonia concentration in the rumen Toxicity from secondary metabolites

Physiologic Regulation on Food Intake(Long term)

Set points. Body appears to have targets for body size and composition. Regulation not fully understood, but the hypothalamus involved. Leptin is a hormone produced by fat that appears to influence food intake.

Acclimization in Food Intake

Most variation in intake occurs with random environmental changes. Steady State experiences Changes with More predictable factors

Adjustment of Intake

Behavioral, Foraging Strategy, Novel Habitats, Physiological, Energy & Nutrient Requirements, Digestive capability

Time for Adjustment of Diet

Turnover Time. Time to replace digestive content. Influenced by size, structure & Function of digestive tract. Efficiency of digestion not optimal until after Turnover time.

Direct Measures of Food Intake

Behavioral Observations, Close Observation of feeding animal, Limited in applicability, Difficult to observe extended feeding cycles

Telemetry(Direct Measures of Food Intake)

Radio attached to animal, then follow with a receiver. Some with GPS. Record areas used by animals. Deduce foraging based on site characteristics.

Measuring Bite Size

Measured by counting bites to consume a known quantity of food. Calculated independently for each food type. Often done in captive situation

Removal Method

Measure available food before and after feeding. Most direct measure of food intake. Difficult to accomplish in Wild. Animal given choice to consume or reject any item.

Digestible Intake

Amount of nutrient retained during digestion. Measured as the mass balance between ingestion & feces

Metabolizable Intake

Amount of nutrient retained after urinary & Gaseous loss. Measure of “true gain” from a food. Accounts for endogenous use. Metabolizability Coefficient is the Fraction food intake retained

Factors that effect Digestibility & Metabolizability of Foods

Dependent on chemical composition, Fiber Content, Secondary Compounds, Digestive Physiology & Anatomy and Digestive Flora

Markers (Indirect Measures)

Used when direct measures unfeasible. Must be validated with direct measures or other indirect. Markers represent a food item as it moves through digestive tract. Must move & act as food

Indigestible Marker

Remain with food throughout digestive tract. Commonly used for transit times.

Digestible Marker

Absorbed in digestive tract, Assimilated into tissues

Chemical Markers

Use unique combination of indigestible components. Waxes, alkanes, Minerals. Create a fingerprint of composition. Identification Dependent on uniqueness of patterns.

Stable Isotope

All elements have several isotopes, atoms that vary in atomic weight. Ratio of heavy to light isotopes vary and can provide information. Expressed as ratio relative to a standard.

Trophic Studies

Ratios of 15N/14N increase as tissue incorporated into higher trophic levels. Predators usually have higher ratio than their prey

C3 Plants

browse, cool season grass, forbs. δ13C = -23 – -30

C4 Plants

Warm season grasses. δ13C = -10 – -14

Tissue turnover of Diet Reconstruction

Bone yrs, RBC 2 mo, Serum 1-2 wk, Liver 1-2 wk, Antler/hair growing period

Quantitative Fatty Acid Signature

Fatty acids crucial to both plants & animals. Energy storage, Membrane function. Fatty acid profiles indicate diet. Very precise. Two groups of essential fatty acids available

Principal Components of Organisms

Water, Dry Matter(Organic Matter and Ash), Minerals

Organic Matter

Measured as Crude Components: Carbohydrates, Proteins, Fats

Allometry

Most relationships to body size not Linear. Metabolic rate (energy expenditure)

Dietary Requirements

Amount of resource (Water, nutrients, Energy) needed by an animal in diet. Nutritional & Dietary Requirements not constant

Dietary Requirements(Energy)

All require source of Oxidizable C. Derived from Carbohydrates, Proteins, Fats

Minimal or Maintenance Requirement

Amount of nutrient needed to maintain body. Does not include activity. Activity costs added to minimal. Zero Balance intake

Optimal Requirement

Level of Nutrient Intake that results in best performance of animal. Growth, Productivity.

Safe & Adequate Range

Most often used in Human and Livestock. Based on acceptable, but suboptimal performance. Minimal Response, Intake Limits to prevent Deficiency or Toxicity