Week 1

Feedstuffs and Nutritional Value

Animal-Based Analyses

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• Objective
• Measure utilization efficiency of each component in a feedstuff
• Used in conjunction with laboratory-based analyses
• Feeding trials
• Compare production results between feeding schemes
• Applied research
• Preliminary trials
• Control and treatment(s)
• Measure production differences
• Digestion trials
• Estimate total amount of specific nutrient absorbed from GI tract
• Two measures
• Apparent digestibility
• Does not account for endogenous sources
• Generally, digestibility measured
• True digestibility
• Does account for endogenous sources
• Procedure
• Determine: feed intake, nutrient intake, feces excreted, nutrient excreted
• Figure 3.9 – Individual feeders for cattle



• Figure 3.10 – Fecal collection bag



• Equation: Digestibility (%) = ((nutrient in – nutrient out) / (nutrient in)) x 100
• Alternatively, use of marker
• External and internal
• Inert
• Equation: Digestibility (%) =  100 – (100 x (marker concentration in feedstuff / marker concentration in feces) x (nutrient concentration in feces / nutrient concentration in feedstuff))
• Used if individual total intake and output cannot be measured
• Balance trials
• Estimate net retention of specific nutrient
• Procedure
• Determine: nutrient intake, nutrient output
• Output via feces, urine, respired air, and sloughed materials
• Require metabolism crate
• Figure 3.11 – Swine metabolism crate



• Energy value of feedstuff – Energy terms
• Figure 3.12 – Terms describing energy value of feedstuff



• Digestible energy (DE)
• Procedure
• Digestion trial
• Determine: total feed energy (GE) and fecal energy (FE)
• Equation: DE = GE – FE
• Metabolizable energy (ME)
• Procedure
• Balance trial
• Determine: total feed energy (GE), fecal energy (FE), urinary energy (UE), and gaseous energy (GE*)
• Equation: ME =GE – (FE + UE + GE*)
• Poultry ration formulation
• Net energy (NE)
• Most accurate value
• Estimates energy available for maintenance and productive functions
• Three NE values: maintenance (NEM), growth (NEG), and production (NEP)
• Procedure
• Balance trial – estimate ME
• Calorimetry – estimate HI
• Heat increment
• Energy loss associated with consumption, digestion, absorption, and metabolism the nutrients for maintenance and productive functions
• Equation: NE = ME – HI
• Ruminant ration formulation
• Energy value of a feedstuff - total digestible nutrients (TDN)
• Estimates energy value of feedstuff
• Procedure
• Determine digestibility of each energy yielding fraction via digestion trials and proximate analysis
• Equation: TDN = (digestible crude protein) + (digestible crude fiber) + (digestible nitrogen-free extract) + (digestible ether extract x 2.25)
• Expressed in units of concentration or mass
• TDN between DE and ME
• Advantages
• Simple
• Disadvantages
• Accuracy – especially fibrous versus nonfibrous feedstuffs