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Isfahan University of Technology Isfahan, Iran Advanced Digestive Physiology (part 2) By: A. Riasi (PhD in Animal Nutrition & Physiology) http://riasi.iut.ac.ir Mastication Teeth in ruminants Mastication Chewing of food is fast and irregular with variable amplitude. During rumination the cud is chewed with: • Much more slowly and evenly • Usually on one side • Occasionally changed to the opposite side Mastication Direct and indirect effects of mastication: • Break the stem and leaf fragments of food and to cud solids into small particles. • Movements of the teeth excite sensory buccal mechanoreceptors. Esophagus The properties of esophagus • It is the least complex section of the digestive tube. • Its role in digestion is simple: To convey boluses of food from the pharynx to the stomach. • Absorption in the esophagus is virtually nil. Esophagus • The mucosa does contain a few mucous glands. • The architecture is that of a typical hollow organ with four layers. • The lamina propria contains a relatively dense connective tissue, with the elastic fibers. Esophagus • Many seromucous glands are present in the submucosa. • In ruminants, glands are present in the cranial third of the esophagus. • Submucosal plexus (Meissner’s) are present but may be quite small. Esophagus • The musculature may be: Skeletal muscle Smooth muscle A mixture of smooth and skeletal muscles Esophagus Contraction of the muscle cells (peristalsis) help to propel the boluses of ingesta toward the stomach. The ruminant stomach and its development The ruminant stomach and its development The wall of stomach is made of 4 layers: • T. Mucosa • T. Submucosa • T. Mascularis • T. Serosa The ruminant stomach and its development The ruminant stomach and its development 1 3 4 2 5 Solid lines: internal oblique fiber (ruminal pillars, lips of reticular groove, omasal pillar); broken lines: longituidal fibers; wave lines: circular fibers. At any given place, there are only two muscle layers in the stomach wall. 1= cardia; 2= reticulum; 3= rumen 4= omasum; 5= abomasum. The ruminant stomach and its development Preruminant stomach and food digestion From birth to about 2 weeks of age, the calf is a monogastric. The abomasums is the only stomach compartment actively involved in digestion. Readily fermentable carbohydrates are important for the rumen development. Size of ruminant stomach compartment Size of ruminant stomach compartment Size of ruminant stomach compartment Pre-ruminant period Pre-ruminant period Coming from esophagus Leading to omasum Size of ruminant stomach compartment Transition from pre-ruminant to ruminant Transition from pre-ruminant to ruminant Absorptive surface area is enhanced by increasing: • Papillae length • Papillae width • Papillae density Transition from pre-ruminant to ruminant Two important factors for stimulating papillae growth: • Presence and absorption of volatile fatty acids (VFAs) in rumen Stimulatory effect of different VFAs is not equal • Rumen epithelial ketogenesis (BHBA production) Transition from pre-ruminant to ruminant A: caudal portion of the caudal ventral blind sac; RB: right side and LB: left side caudal dorsal sac; RC: right side and LC: left side cranial dorsal sac; RD: right side and LD: left side cranial ventral sac; and RE: right side and LE: left side ventral portion of caudal ventral blind sac (Lesmeister et al. (2004) Transition from pre-ruminant to ruminant Undeveloped Rumen Developed Rumen Transition from pre-ruminant to ruminant Milk only Milk and grain Milk and hay Importance of diet to rumen development (6 weeks of age) Transition from pre-ruminant to ruminant Milk, hay and grain Milk and hay Transition from pre-ruminant to ruminant Five factors affect the rumen development: Establishment of bacteria in the rumen Liquid in the rumen Outflow of material from the rumen Absorptive ability of the tissue Substrate available in the rumen. Establishment of bacteria in the rumen At birth day the rumen is sterile • Aerobic bacteria • Change of bacteria population Establishment of bacteria in the rumen Prolonged milk feeding may retard: • Typical ruminal microflora • Establishment of protozoa Establishment of bacteria in the rumen Factors may affect calf’s rumen microflora • Feeds • Environment • Bedding • Hair Establishment of bacteria in the rumen The numbers of total bacteria Change in types of bacteria by feeding DM: • Decreasing aerobic bacteria • Increasing anaerobic bacteria Establishing a rumen microflora Establishment of bacteria in the rumen Liquids in the rumen Milk does not help rumen development at all Water is essential for rumen development • Without sufficient water, bacteria cannot grow, and ruminal development is slowed. Outflow of material from the rumen Measures of ruminal activity: • Rumen contractions • Rumen pressure • Regurgitation (cud chewing) Little muscular activity at birth. Outflow of material from the rumen Solid feed intake stimulates: • Rumen microbial proliferation • Production of microbial end products Outflow of material from the rumen Effect of chemical composition of concentrates: • A shift in the microbial population • Increasing butyrate and propionate production at the expense of acetate. Outflow of material from the rumen Forages, have an increased ability to maintain a higher ruminal pH, due to: • A larger particle size • An increased fiber content Outflow of material from the rumen 1393 ،برگرفته از میرزایی و همکاران Absorptive ability of the rumen tissue The rumen wall consists of two layers: • The epithelial • The muscular Absorptive ability of the rumen tissue The end-products of fermentation. Butyrate and propionate absorbed by rumen epithelium. most readily Availability of substrate The primary factor determining ruminal development is dry feed intake. • Starter • Proper stimulation for rumen development Rumen parakeratosis Parakeratosis have some adverse effects: • Creating a physical barrier. • Restricting absorptive surface area and volatile fatty acid absorption. • Reducing epithelial blood flow and rumen motility • Causing papillae degeneration and sloughing in extreme cases. Rumen parakeratosis Initial evidence of parakeratosis is papillae clumping and branching. • Followed sloughing. by papillae degeneration and Rumen parakeratosis Concentrate diets: • Increased volatile fatty acid production • Decreased rumen buffering capacity • Subsequently decreased rumen pH Rumen parakeratosis Increased feed particle size: • Maintains epithelial and papillae integrity and absorptive ability. • Increased rumination and rumen motility • Increased salivary flow and buffering capacity • Development of mature rumen function and environment. Changes in rumen muscularization Feed physical structure: • Development of rumen muscularization • Development of rumen volume • Stimulation of rumen motility Changes in rumen muscularization Understanding the cellular biology and physiological changes of rumen development: • Neonatal calf digestion kinetics • Development of low-impact or non-invasive research procedures could be instrumental in advancing this area further. Physiology and ontogeny of rumen development Two important aspects for development of rumen: • Ruminal growth and cellular differentiation • A major shift in the pattern of nutrients being delivered to the intestine and liver Thus nutrient delivered to peripheral tissues Control of ruminal epithelial cell proliferation In vivo and in vitro studies using mitotic indices for ruminal epithelial cell proliferation. • Butyrate may induce a mitotic proliferation • Propionate and acetate have been shown to stimulate mitotic indices Control of ruminal epithelial cell proliferation Contradiction in response to VFAs by in vivo and in vitro. • The differences may be attributed to indirect pathways during in vivo condition. Control of ruminal epithelial cell proliferation Some hormones and growth factors may have mediator effect: • Insulin, Pentagastrin, Glucagon • IGF-1, Epidermal growth factor • Cortisol Neonatal ruminal epithelial metabolism In neonatal ruminant primary source of energetic substrates are blood borne, derived from intestinally absorbed nutrients. Difference between neonate and mature ruminant for uptake of oxidizable substrates by ruminal cells Neonatal ruminal epithelial metabolism Ontogenic control of some of the critical development changes of rumen: • Increase in gene transcripts for 3-hydroxy-3methylglutaryyl-CoA synthase. Liver metabolism & rumen development The liver undergoes a maturation process of its own in response to ruminal development • The most notable of changes is the shift from a glycolytic to glucogenic liver. Liver metabolism & rumen development Liver adaptation in the developing animals: • Shift from primarily intestinally absorbed glucose, long-chain fatty acids, and milk-derived amino acids to SCFA, ketones, amino acids from feed and microbial sources, and other dietary compounds. Liver metabolism & rumen development A basic reduction in enzyme capacity for hepatic glucose oxidation via glycolytic and hexose monophosphate pathways: • Glucose-6- phosphate dehydrogenase • 6-phosphogluconate dehydrogenase • Fructose 1,6-bisphosphate aldolase • Glyceraldehyde 3- phosphate dehydrogenase Liver metabolism & rumen development A rapid increase in activity of hepatic gluconeogenic enzymes: • Glucose 6-phosphatase activity having been shown to double during this period Bloat in young ruminant animals Bloat can affect either: • Abomasum • Rumen Abomasal bloat is often rapidly progressive and life threatening. Bloat in young ruminant animals Factors contributing to abomasal bloat: • Overfeeding milk • Feeding milk too fast • Pathogens, such as Clostridium Bloat in young ruminant animals Clostridium perfringens types A, B, C Clostridia are normally found in the intestine of cattle and can survive for months in the soil. Bloat in young ruminant animals Overeating or abrupt diet changes tend to: • Produce indigestion that slows gut movement • Providing the sugars, proteins and lack of oxygen needed for rapid growth of Clostridia • Wet conditions also seem to favor this organism Bloat in young ruminant animals The other factors: • Impaction of the abomasum or intestines with non- feed substances such as bedding or hairballs • Structural or physiological problems with the abomasum Bloat in young ruminant animals Management practices to consider include: • • • • • • • • Colostrum management Feeding time Milk temperature Feeding equipment Antibiotics Feed ingredients Stress Health status