Rumen Development

Gut Function After Birth Digestion and absorption similar to monogastric Function of the reticular groove Enzyme activity of saliva, stomach and small intestine different than in adult ruminant Rumen volume and papillae must develop Rumen microflora must become established Length of transition period between “functional non-ruminant” to “fully functional ruminant” is heavily diet-dependent

Rumen Development Newborn rumen is nonfunctional Sterile, small, lack papillae Reticular groove shunts milk from esophagus to abomasum Rumen developed by Exposure to environment & other ruminants Consumption of solid feed Consumption of water Controlled by the producer if animal is separated from dam

Rumen Development Undeveloped Rumen Developed Rumen

Size of Ruminant Stomach Compartments Adult, % Newborn, % Rumen 55 29 Reticulum 7 6 Omasum 24 14 Abomasum 51

Reticular Groove Reticular groove is composed of two lips of tissue that run from the cardiac sphincter to the reticulo-omasal orifice Transport milk directly from the esophagus to the abomasum Closure is stimulated by: Suckling Consumption of milk proteins Consumption of glucose solutions Consumption of sodium salts NaHCO3 Effective in calves, but not lambs Presence of copper sulfate Effective in lambs

Reticular Groove Reflex Reflex similar in bucket-fed and nipple-fed calves until 12 weeks of age Reflex normally lost in bucket-fed calves by 12 weeks Reflex normally lost in nipple-fed calves by 16 weeks of age, but effectiveness decreases with age Considerable variation Can sometimes be induced in mature animals Advantages of nipple-feeding compared to bucket-feeding in shunting milk through groove Positioning of calf Arched neck Rate and pattern of consumption of milk Slower and smaller amounts consumed Increased saliva flow Salivary salts stimulate closure                

Site of Digestion in Young Ruminants

Nutritional Impact of Rumen By-Pass More efficient use of energy and protein No methane losses, heat of fermentation or ammonia losses Requirements (100 kg calf gaining 1 kg/day) Metabolizable Digestible energy protein (MJ) (gm) Preruminant 32.5 280 Ruminant 35.1 290 Require B vitamins in diet (no microbial synthesis) Unable to utilize non-protein nitrogen

Rennin in Neonate Produced by gastric mucosa in newborns Coagulates milk proteins (caseins) Curd encases whey proteins, fats, and other associated nutrients within minutes Curd slowly contracts Formation and contraction of curd allows slow release of nutrients to small intestine, increases digestibility optimal pH for activity Rennin Pepsin Proteolytic activity 3.5 2.1 Curd formation 6.5 5.3

Enzymes for Protein Digestion Pepsin May or may not be secreted as pepsinogen HCl secretion is inadequate in newborn ruminant to lower abomasal pH enough for pepsin activity Ruminants born with few parietal cells Reach mature level in 31 days Pancreatic proteases Activity is low at birth Activity increases rapidly in first days after birth Mature levels of pancreatic proteases reached at ~2 months of age

Enzymes for Carbohydrate Digestion Intestinal lactase Activity high at birth Decrease in activity after birth is diet dependent Weaning decreases activity – substrate is no longer present Pancreatic amylase Activity is low at birth Activity increases 26-fold by 8 weeks of age Mature levels not reached until 5 to 6 months of age Intestinal maltase Low at birth Increases to mature levels by 8 to 14 weeks of age independent of diet Intestinal sucrase – never present in ruminants

Enzymes for Lipid Digestion Pregastric esterase Secreted in the saliva until 3 months of age Activity is increased by nipple-feeding Activity is greater in calves fed milk than those fed hay Hydrolytic activity is adapted to milk fat Most activity occurs in the curd in the abomasum 50% of triglycerides in milk are hydrolyzed in 30 minutes Pancreatic lipase Secretion is low at birth Increases 3x to mature levels by 8 days Hydrolyzes both short and long chain fatty acids

Digestive Efficiency of Lipids Preruminants can make effective use of a variety of fats Digestibility Butterfat 97 Coconut oil (can’t be fed alone) 95 Lard 92 Corn oil 88 Tallow 87

Factors Required for Rumen Development Establishment of bacteria Water-based environment Free water intake Development of muscular tissue Rumen contractions Absorptive ability of tissue Rumen papillae Substrate availability Dry feed intake

Rumen Development Rumen epithelium and papillae development stimulated by butyrate (from fermentation of concentrates) Increase in rumen capacity developed by forage intake Papillae integrity developed by diet abrasiveness Prevents papillae clumping and excessive keratin (a wax secreted by rumen epithelium) accumulation on surface of rumen papillae Increases absorptive function

Absorptive Ability of the Rumen VFA absorption (mg/100 mg/hr) The ability of the rumen to absorb VFA is thought to depend on production of VFA Offering dry feed from an early age will promote production of absorptive ability Increase papillae development, increase surface area, increase absorptive ability Hay + grain Milk / grain Milk

Importance of Diet to Rumen Development (6 weeks of age) Milk only Milk and grain Milk and hay

Importance of Diet to Rumen Development (12 weeks of age) Milk, hay and grain Milk and hay

Establishing a Rumen Microflora Normal microflora established by animal-to-animal contact Bacteria will still establish if calves are kept separate from mature animals – protozoa will not Microbes also introduced through environment Feed sources Contaminated housing, bedding Favorable environment for growth: Presence of substrates Optimal ruminal pH Water for fluid environment Optimal rumen temperature

Bacteria in the Rumen At birth the rumen is sterile - NO bacteria By 24 hr of age there is a large number of bacteria - mostly aerobes With dry feed intake, typical rumen bacteria are established Proteolytic Methanogenic Cellulolytic S. bovis

Development of Rumen Microflora 1st Appear Reach Peak Type of Organisms 5-8 hours 4 days E. Coli, Clostridium welchii Streptococcus bovis ½ week 3 weeks Lactobacilli ½ week 5 weeks Lactic-acid utilizing bacteria ½ week 6 weeks Amylolytic bacteria B. ruminicola – week 6 1 week 6 to 10 weeks Cellulolytic bacteria Methanogenic bacteria Butyrvibrio – week 1 Ruminococcus – week 3 Fibrobacter succinogenes – week 6 1 week 12 weeks Proteolytic bacteria 3 weeks 5 to 9 weeks Protozoa - 5 to 13 weeks Normal microbial population

Outflow from the Rumen Unfermented material must leave the rumen Muscular action in the rumen begins very early in life (4-6 days) and may depend on establishment of bacteria – associated with onset of feeding grains Regurgitation has been seen as early as 3 days of age Forage intake is an early instinct in ruminants

Can A Ruminant Survive Without A Rumen??? Rumenectomies (early removal of the rumen) or prolonged milk feeding used to answer this question Young ruminants will survive for a time without rumen fermentation Animal viability decreases and sudden death occurs between 6 and 8 months of age Can be reversed almost immediately by providing food to the rumen!!! Ruminant animals “hard-wired” metabolically to function as ruminants Must utilize the end-products of microbial fermentation