CHO Metabolism CHO Metabolism - CHO constitute 70% or more of the DM - Major precursor of energy - Partitioning CHO into fiber & non-fiber CHO Metabolism Optimal utilization of diets influenced by: - Chemical composition - Physical characteristics (particle size & density - Physical characteristics can influence: animal health, ruminal fermentation & utilization, & animal performance. - Fiber: Slowly digestible or indigestible fraction - NDF measures total fiber - NDF relates to: Intake, feed density, chewing activity, digestibility, rate of digestion & milk fat production CHO Metabolism Fiber Chewing Acid Production Fiber Chewing Salivary buffer Ruminal pH A:P ratio milk fat Non-fibrous CHO (NFC)= 100- ( NDF+CP+EE+Ash) Nonstructural CHO (NSC)=Analytical method •NFC NSC •Lower ruminal pH result of too much NFC or NSC Neutral Detergent Soluble CHOH A calculated value: NDSC = 100 - (%NDF+%CP+%Fat+%Ash) NDF corrected for protein • 98% potentially digestible in the rumen • Rapidly fermented in the rumen • Diverse group and not easily measured directly in feeds • Not all digested by mammalian enzymes Effective Fiber refer to ability of fiber to maintain milk fat production and animal health effectively Physical effective NDF (peNDF)= related to physical characteristics of fiber (primarily particle size) that influence chewing activity and the biphasic nature of ruminal contents (floating mat of large particles on a pool of liquid and small particles) Pe NDF relates only to the physical properties of fiber •peNDF is a more restricted term and concept than NDF •peNDF of a feed is the product of its NDF concentration and its physically effectiveness factor (pef) •Pef varies from 0, when NDF is not effective in stimulating chewing activity, to 1 when NDF is fully effective in promoting chewing peNDF is related to animal health and milk fat depression, because ruminal pH and the pattern of fermentation is a function of: production of salivary buffers during eating and rumination. •Chewing activity / Kg DM varies with: 1) breed, 2) size, 3) level of intake, 4) fiber content, and 5) particle size. •The animal response that is associated with eNDF is milk fat percentage. •Effectiveness factor for NDF can vary from 0, when a feed has no ability to maintain milk fat percentage , to values greater than 1.0 when a feed maintain milk fat percentage more effectively than it maintain chewing activity. CHO Metabolism Logically peNDF and eNDF should be highly correlated eNDF can be greater than peNDF for feeds that maintain milk fat percentage but do not stimulate chewing activity to a similar extent (e.g., feeds containing fats or intrinsic buffering capacity). •Conversely, eNDF can be less than peNDF for feeds that detrimentally affect ruminal fermentation and milk fat production without affecting chewing activity (e.g., feeds containing sugars). •Non-fiber facotrs of feeds that influence milk fat synthesis are included in eNDF, but not peNDF. •Because eNDF is related to intrinsic pH buffering and neutralizing capacity, fat concentration and composition, acid producing during fermentation, pH changes reflecting the balance of buffering capacity and acid production, shift in VFA amounts and ratio produced, and metabolic changes that influence secretion of milk fat Laboratory assessment of fiber effectiveness NDF method proposed by Robertson and Van Soest Particles retained on a 1.18 mm sieve have a high resistance to passage from the rumen of both cattle and sheep •A simple system for estimating peNDF from chemical and physical measurements in the laboratory can be based on NDF concentration and the proportion of particles that are retained on a 1.18 mm sieve. •Another method for estimating eNDF is using Pen state separator Biological Assessment of Fiber Effectiveness First step is developing a scale for assessing pe is to define a reference against which all feeds are compared A hypothetical std that would result in the max amount of chewing/ Kg DM or NDF. The reference feed should be a long grass hay containing 100% NDF that is assigned a pef of 1.0 resulting in a peNDF of 100. •Chewing/ Kg of NDF increase as the NDF in long forage increase (Table 1). •Particle size reduction decrease chewing activity/ Kg NDF (Table 2). •Chopping forages to 4 cm reduced total chewing activity to 80% of the unchopped forage. • Grinding forage reduce chewing activity to 20-60% of that for long forage. Measurement of in vivo digestion kinetics Total tract digestibility direct: total fecal collection indirect:markers CHO Metabolism peNDF is related to fiber concentration, particle size, and particle size reduction, so peNDF is related to the formation of ruminal mat, which may be a critical factor for selectively retaining fiber in the rumen, determining the dynamics of ruminal fermentation and passage and stimulating rumination.
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