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TAMU ANSC 318 - Properties of Digestion Calculations
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ANSC 318 1st Edition Lecture 6 Outline of Last Lecture I. Chemical-Based and Nondestructive Methods of Evaluation of Feedstuffs Outline of Current Lecture II. Chemical Evaluation of Feeds VS. Nutrient Digestibilitya. Apparent vs. True Digestibilityb. Methods to Determine DigestibilityIII. Digestion Trialsa. Digestibility Calculationsb. Example CalculationsIV. Factors Affecting Apparent Digestibilitya. Effect of Dietary ADF Content on Digestibilityb. Associative Effects on DigestibilityV. Total Digestible Nutrients a. WeaknessesCurrent Lecture (** = need to know)Chemical Evaluation Vs Nutrient Digestibility-Potential value of feed is measured by chemical analysis *-Actual or useful value of a feed to an animal can be determined only after making allowances for losses like digestion, absorption, and metabolism-Digestibility: feed that is not excreted in the feces, assumed to be absorbed by the animal-feces accounts for the largest loss in nutrients during digestion-Gross Energy (GE) = potential energy from feed-Net Energy (NE) = GE – losses (feces, urine, metabolism, heat)Apparent vs. True Digestibility:-digestibility is typically referred to as apparent digestibility-termed “apparent” because not all fecal matter excreted by an animal represents undigested feed-Fecal Material: undigested feed + non feed material or endogenous fecal material ***•undigested microbes from rumen fermentation and fermentation in cecum/largeintestine•Digestive enzymes and mucousThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.•sloughed intestinal cellsMethods to Determine Nutrient Digestibility:-Conventional Digestion Trial: most accurate method of measuring digestibility (Gold-standard Method)-Objective of Trial: accurately quantify nutrients consumed and excreted in feces for aparticular feed or diet over a given time periodDigestion Trial Procedures-train animals for trial (adapt them to test diet, confine animals to metabolism crate/stall)-feed animals a known amount each day and collect feed refusal-collect and weigh fecal output each day (separate urine and feces to avoid contamination)-typically conducted over 7-day time period-prepare feed and fecal samples for lab analysis (conduct nutrient analysis and calculate digestibility)-can be conducted using any speciesDigestibility Calculations:Apparent Nutrient Digestibility (%) = ((Nutrients In – Nutrients Out)/Nutrients In) x 100Example Calculations (DM Digestibility) Sheep consumes  1050 g of hay/day (89% DM)1050 x .89 = 934.5 g feed DM per daySheep excretes  972 g feces per day (40% DM)972 x .40 = 389 g fecal DM per dayDigestible DM  ((934.5-389)/934.5) x 100 = 58.4%Factors Affecting Apparent DigestibilityI. Nutrient Composition of Feed:-digestion is closely related to chemical composition-both amount of NDF and type (lignin fraction of NDF) greatly affect digestion (↑NDF = ↓ digestibility)-there is a greater variability of digestion within roughage feeds than concentratesII. Forage Maturity:-as a plant approaches maturity, nutrient composition changes (↓ leaves and ↑ stems) ***-as plant matures, cell wall content (NDF) increases, ↑ fiber and ↓ digestibility-↑ starch = ↑ digestibility-↑ fat = ↑ digestibilityEffect of Dietary ADF Content on Digestibility:-ADF is more accurate for depicting digestibility-relationships are not always accurate, very large spectrum for errorIII. Level of Feed Intake:Ranges in Feed Intake:Species Range of Feed Intake (multiple of maintenance)Growing Cattle 2.0 to 2.5Growing Pigs 2.5 to 3.5Poultry 2.0 to 3.0Lactating Dairy Cows 3.0 to 5.0Lactating Sows 3.0 to 5.0-when an animal is at maintenance they are not producing or losing anything (bare minimum)-Lactating animals require the highest because of milk production-In ruminants, digestibility is depressed by about 4% for each multiple increase in intake when compared to maintenance ****DM Intake (lbs.) Level of Maintenance Mult. Digestibility12 1X 70%24 2X 66%36 3X 62%-Intake does not affect nonruminant digestibility when low-fiber diets are fed **-horses are somewhere in the middle of the other 2IV. Associative Effects or Non-Additivity:-the nonadditive differences between a feed fed within a ration and the same feed fedby itself-influence one feed has on another when fed in combination ******-occur mainly in ruminants when fed high-levels of intake-2 + 2 does NOT always = 4-there is the digestibility of the additive (forage or grain) by itself (2+2=4)-the digestibility of the additive when fed with something that has a negative impact ondigestion (2+2=3)-and the digestibility of the additive when fed with something that has a positive impacton digestion (2+2=5)-silage/grain mixes seen to have cause the biggest depression in digestionV. Feed Processing:-affects digestibility-grinding/pelleting a forage will ↓ digestibility-Processing a forage will ↑ rate of passage through the GIT which ↓ time available fordigestion-Processing a grain will ↑ digestion -all of these apply mainly in ruminantsVI. Environmental Temperatures:-digestibility decreases with exposure to cold (↓ temp = ↓ digestibility) **-heat does not affect digestibility **-↓ temp = ↑ intake (energy) = ↑ rate of passage through GIT = ↓ digestion (happens inall speciesVII. Plant Selection:-In situ nylon-bag procedure (NBDMD) has been one of the principle selection criteriafor bermudagrass breeding at Tifton, GA-genetic gains in NBDMD averaged 2 g per kg forage per year between 1963 and 1993-a 3.8% higher NBDMD provided a 9% improvement in BW of steersTotal Digestible Nutrients (TDN):-measures feed’s energy value-uses proximate analysis system-requires measurement of nutrient digestibility coefficient-need chemical composition-expressed as a % (remember to multiply fat % by 2.25 before adding total)-good way to express energy value in feedsWeaknesses of the TDN System:-limitations of system to accurately separate CF vs NFE **-does not account for energy losses: urine, combustible gas (methane), and heatincrement; main weakness *******-only accounts for loss of fecal matter-gaseous energy and heat increment losses in roughage > losses in grain-type feeds ****-roughages usually overestimated and grains usually underestimated-when comparing TDN, take losses into consideration, ↓ loss = ↑


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TAMU ANSC 318 - Properties of Digestion Calculations

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