Topic 6: Nutrient Requirements Flashcards

This set covers definitions and methods related to nutrient requirements, availability testing, and endogenous loss calculations for animal nutrition.

Nutrient

Any chemical element or compound in the diet that supports maintenance of life processes or normal production processes such as reproduction, growth, and lactation.

Essential Nutrients

Nutrients that must be in the diet for optimal health and productivity because they cannot be synthesized by the animal, or the rate of synthesis is insufficient to meet metabolic demands.

Conditionally Essential Nutrients

Nutrients that are essential under specific dietary situations, such as tyrosine (phenylalanine) and cystine (methionine).

Basal Nutrient Requirement

The minimal amount of a nutrient needed to replace obligatory losses.

Maintenance Nutrient Requirement

The amount of a nutrient needed to sustain a steady state and support essential life processes.

Total Nutrient Requirement

The sum total of nutrient needs for all purposes, calculated as Maintenance + Production (growth, reproduction, work).

Empirical Method

A method to determine nutrient requirements by feeding animals experimental diets containing graded nutrient levels to find the level that optimizes health and performance.

Factorial Summation

A method of determining nutrient requirements by summing the needs for specific functions and identifying all physiological processes that use the nutrient.

Depletion Studies

A method where nutrient intake is varied to relate to deficiency; the requirement is considered the lowest intake that shows no sign of deficiency or tissue store depletion.

Balance Studies

A method that varies nutrient intake and measures the difference between intake and output; the requirement is the intake that achieves zero balance.

Total Collection Method

A nutrient balance method requiring a careful record and collection of total feed intake and total fecal, urinary, or excreta output.

Index Method

A nutrient balance method that requires a dietary marker and allows for partial sampling of output.

Production Studies

A method that varies nutrient intake and measures outputs like growth or reproductive output (milk, eggs) to find the intake that maximizes and optimizes production.

Isotope Studies

A method using labeled nutrients to measure nutrient metabolism and/or turnover (flux).

Daily Requirement Expression

A form of expression on an intake basis, such as $mg\,day^{-1}$ or $mg\,kg^{-1}$ body mass $day^{-1}$; considered the most accurate expression form.

Dietary Requirement Expression

A form of expression on a concentration basis, such as % of diet or $g\,kg^{-1}$ diet; it is practical for diet formulation but dependent on food intake.

Direct Procedures

Nutrient availability methods where a test feed ingredient is formulated as the sole source of energy in the test diet.

Substitution Method

A difference procedure where a known proportion of a basal control diet is substituted with a test ingredient in a single point substitution.

Regression Method (Availability)

A difference procedure using multiple point substitution of a test ingredient and extrapolating to 100% replacement.

Exogenous Component

The part of fecal nutrient content consisting of undigested food residues.

Endogenous Component

Unavoidable fecal secretions occurring regardless of diet, including epithelial cells, enzymes, and mucus.

Fasting Trials

A method to measure endogenous losses where feed is withheld for 24 to 48 hours to empty dietary residues from the digestive tract.

Regression Method (Endogenous)

A method where fecal nutrient output is regressed against intake levels; basal endogenous loss is indicated by the y-intercept (output when intake is zero).

Nutrient-free Diets

Diets that exclude a specific nutrient (e.g., protein-free or nitrogen-free) to measure basal endogenous losses without interference from dietary intake.