Animal Science 320, Week 3 Notes
Animal Science 320, Week 3 Notes AN S 320
Popular in Animal Feeds and Feeding
Popular in Animal Science
This 3 page Class Notes was uploaded by Danielle Garrison on Sunday September 11, 2016. The Class Notes belongs to AN S 320 at Iowa State University taught by Morris in Fall 2016. Since its upload, it has received 10 views. For similar materials see Animal Feeds and Feeding in Animal Science at Iowa State University.
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Date Created: 09/11/16
Feed Efficiency and Digestibility (Chapter 5) Objectives: o Explain feed efficiency o Calculate gross feed efficiency and feed conversion ratio o Explain relative feed efficiency among species (most to least efficient) o Calculate digestibility o Understand digestibility experimental design Feed Efficiency: o Major contributor to profitability – 70% of operation costs o Food – need to produce product from given species o Beef – least efficient; fish – most efficient Beef – sheep – swine – poultry – dairy – fish o Importance: Increase of global population and need for food Reduced resources (feed) Drives production profitability o How to measure: Gross Feed Efficiency – live wgt gain per intake Gain/intake Also known as “gain to feed” ratio Higher number better – animals gaining more on less feed Feed Conversion Ratio (FCR) – intake per live weight gain Intake/gain Also known as “Feed to gain” Lower number better – animals eating less per amount of gain o Improvements: Poultry – 250% since ‘57 Beef - .05 lb every 25 years; minimal change last 10 years High maintenance requirement Large ruminant (fermentation – lot of feed resources) Purpose of feed digestibility: improving this improves feed efficiency o Evaluate and quantify available nutrients from individual feed ingredients Proximate analysis – what’s in there but not how it’s used by animal o Evaluate and quantify available nutrients from diets o Look at average energy concentration of feeds (TDN) o Partition digestion of nutrients in different compartments of digestive tract Important measures – digestibility trials o Accurate feed intake Include weight of orts (spilled food) o Accurate fecal output o Appropriate diet samples Digestion trials o Animal in metabolism stall or crate Accurate feed intake and fecal collection o Without stalls Collection bags – slot for manure and urine; giant diapers Calan gates – at dairys, key on their neck, have to go into their individual assigned stalls to eat Marker o Adjustment period 1 10-14 days Free digestive tract prior of undigested feed Get animals used to environment Feed at constant rate Isocalorically – maintain body wgt; all animals have same energy diet Some feed isantrogenously – same N or CP intake 90% ad libitium No collection of feces or urine o Collection period Next 4-7 days Monogastrics 3-5 days Ruminants 5-7 days Record feed intake – must be accurate Collect ALL feces excreted and weigh Large animals – collect 5-10% subsample Small animals – 100% fecal sample o Post collection Determine chemical component and/or energy concentration of feed samples, feces, orts Calculate orts for nutrients (depends on feed and species) Calculate digestibility Digestibility% = consumed – excreted/ consumed x 100 Digestibility calculations: o Dry Matter Intake (DMI) – avg amount of feed (as fed) x %DM of feed Smaller than as fed intake o Fecal Output (FO) – avg amount feces excreted x %DM (feces) o DM digestibility (DMD) – (DMI – FO)/ DMI x 100% o Limitations of digestibility trials 1. Apparent Digestion Feces composed of undigested nutrients and endogenous materials that didn’t come from diet o Sloughed mucosa cells, bacteria, and enzymes bile salts Determine true digestion o End materials accounted for and removed from FO Done by: lleal cannula (swine, dog) or ceca removal (poultry) Used for AA digestibility (monogastrics; important for swine) 2. Limit fed animals (90% intake), alter passage rate 3. Spillage and wastage of feed or feces 4. Errors in analyses 5. Orting and selection of feeds – uses TMRs (total mixed rations) o Methods in determining digestibility in producing animals Fecal pans, bags – need to know individual feed intake Digestible markers and indicators – added to certain known amount Physiology inert (don’t do anything), contain no element under investigation readily determined chemically, advantage – researched doesn’t have to collect all feces Example: carmine, titanium oxide, acid insoluble ash (AIA), chromic oxide Factors affecting digestibility o Stage of animal, particle size, disease state, stress, feed source and composition, level of intake, rate of passage (slow – increase fermentation, fast – incomplete digestion), nutrient imbalance, matrices different than individual feeds used Metabolism or balance trails – different than digestive trials o Uses losses in urine o More precise measure of nutrient retention o Commonly done for N to measure protein gain or loss – N balance studies o Determine Biological Value of proteins % of true absorbed protein for productive body functions
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