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 Digestibility a Apparent vs True Digestibility b Methods to Determine Digestibility III Digestion Trials a Digestibility Calculations b Example Calculations IV Factors Affecting Apparent Digestibility a Effect of Dietary ADF Content on Digestibility b Associative Effects on Digestibility V Total Digestible Nutrients a Weaknesses Current 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 large intestine Digestive enzymes and mucous These 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 cells Methods 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 a particular feed or diet over a given time period Digestion 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 species Digestibility Calculations Apparent Nutrient Digestibility Nutrients In Nutrients Out Nutrients In x 100 Example Calculations DM Digestibility Sheep consumes 1050 g of hay day 89 DM 1050 x 89 934 5 g feed DM per day Sheep excretes 972 g feces per day 40 DM 972 x 40 389 g fecal DM per day Digestible DM 934 5 389 934 5 x 100 58 4 Factors Affecting Apparent Digestibility I 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 concentrates II 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 digestibility Effect of Dietary ADF Content on Digestibility ADF is more accurate for depicting digestibility relationships are not always accurate very large spectrum for error III Level of Feed Intake Ranges in Feed Intake Species Range of Feed Intake multiple of maintenance Growing Cattle 2 0 to 2 5 Growing Pigs 2 5 to 3 5 Poultry 2 0 to 3 0 Lactating Dairy Cows 3 0 to 5 0 Lactating 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 Digestibility 12 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 2 IV Associative Effects or Non Additivity the nonadditive differences between a feed fed within a ration and the same feed fed by 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 on digestion 2 2 3 and the digestibility of the additive when fed with something that has a positive impact on digestion 2 2 5 silage grain mixes seen to have cause the biggest depression in digestion V Feed Processing affects digestibility grinding pelleting a forage will digestibility Processing a forage will rate of passage through the GIT which time available for digestion Processing a grain will digestion all of these apply mainly in ruminants VI 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 in all species VII Plant Selection In situ nylon bag procedure NBDMD has been one of the principle selection criteria for 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 steers Total 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 feeds Weaknesses of the TDN System limitations of system to accurately separate CF vs NFE does not account for energy losses urine combustible gas methane and heat increment 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 growth