Dairy Nutrition VCSN642

James D. Ferguson, VMD, MS
Section Animal Production Systems
ferguson@vet.upenn.edu

A. Dairy cows are ruminants

B. Rumen Physiology: A Review

The interior surface of the rumen forms numerous papillae that vary in shape and size from short and pointed to long and foliate.
Reticular epithelium is thrown into folds that form polygonal cells that give it a reticular, honey-combed appearance. Numerous small papillae stud the interior floors of these cells.
The inside of the omasum is thrown into broad longitudinal folds or leaves reminiscent of the pages in a book (a lay term for the omasum is the 'book'). The omasal folds, which in life are packed with finely ground ingesta, have been estimated to represent roughly one-third of the total surface area of the forestomachs.
Source: Colorado State, http://www.vivo.colostate.edu/hbooks/pathphys/digestion/herbivores/rumen_anat.html, June 25, 2009

	3. Rumen – Main site of fermentation
		a. function is to mix and retain digesta for microbial digestion
		b. anaerobic environment, stable pH, particle size for retention, and particle size reduction for removal
			i. saliva provides buffering and minerals for microbial fermentation
				(1) >40 gallons/day
				(2) amount is a function of chewing
			ii. optimal pH 5.8 to 6.4
				(1) pH below 5.8 inhibits fiber digestion
			iii. adequate particle size for rumen retention
				(1) stratification of layers in the rumen – rumen mat
				(2) less dense, longer material on top with denser, smaller particles sinking to bottom
				(3) adequate mat important to control rate of passage and extent of rumen fermentation of feed material
			iv. particle reduction for digestion and passage
				(1) rumination of long material
				(2) smaller particles pass more quickly
			v. copious gas production and dorsal gas cap
				(1) CO2  and CH4 : 3 parts CO2 to 1 part CH4
				(2) belching important to remove gas
				(3) production of methane important to remove H
		c. rich population of microbes
			i. bacteria - 1010 to 1011 cells/gram of rumen contents (60 – 90% of microbial mass)
				(1) cocci
				(2) rods
				(3) spirilla
				(4) 8 distinct groups
					(a) Structural carbohydrate fermentors
						(i) Cellulolytic
						(ii) Hemicellulolytic
					(b) Pectinolytic
					(c) Ureolytic
					(d) Nonstructural carbohydrate fermentors
						(i) Sugar utilizing
						(ii) Amylolytic
						(iii) Organic acid fermentors
					(e) Proteolytic
					(f) Lipid utilizing
					(g) Methane producing
					(h) Ammonia producing
				(5) Fiber fermenting organisms grow more slowly than the non-fiber carbohydrate fermenting organisms
					(a) Fiber digestors prefer a pH of 6.2 to 6.8
					(b) Starch digestors prefer a pH of 5.2 to 6.0
				(6) bacteria are found in the rumen liquid (25%),  attached to feed particles (70%), and rumen epithelium (5%)
				(7) To remain in the rumen, the bacteria reproductive rate must be shorter than the rumen turnover rate
					(a) Slower fermentors attach to particles, as retention in rumen is longer than for liquid
				(8) Diet will influence the proportions of populations in the rumen
					(a) Adaption to feed ingredients and major changes in nutrient concentration is important
					(b) Especially changes in starch and fiber content
				(9) Sudden shift to high starch diets
					(a) Lactic acid tolerant bacteria increase
					(b) Lactic acid utilizing bacteria increase slowly
					(c) Lactic acid accumulates and pH drops below 5.5
			ii. Fungi (5 to 10% of microbial mass)
				(1) exact role is not clear, but are found attached to plant cell wall
				(2) may aid bacteria in penetration of cell wall, improving fiber digestion
				(3) low rates of turnover and are particle associated
				(4) rhizoids penetrate plant cell wall
			iii. protozoa (predation; holotichs, entodiniomorphs; 10 – 40% of microbial mass)
				(1) ingest bacteria and starch particles (and protein)
				(2) population shifts with different dietary ingredients
			iv. microbial groups form syntrophic groups which increase efficiency of energy resources
		d. fermentation
			i. carbohydrates
				(1) most of the starch and sugar fermented to VFA
				(2) fermentation of fiber depends on quality and passage rate
				(3) VFA’s produced acetate, propionate and butyrate
					(a) Acetate predominates: 50 to 60% of VFA
					(b) Propionate: 18 to 20% of VFA
					(c) Butyrate: 12 to 18% of VFA
					(d) Ratios influenced by forage to concentrate ratio
				(4) VFA’s are passively absorbed across rumen wall
					(a) Increasing chain length increases absorption
					(b) Lower pH increases absorption, VFA in neutral state
					(c) Butyrate metabolized by rumen wall to beta-hydroxy butyrate
				(5) Lactate produced by starch utilizing bacteria, which is fermented to Ac, Pr, B
					(a) Lactate is rapidly absorbed across rumen wall and can contribute to metabolic acidosis
			ii. Protein
				learn more about protein in dairy cows
				(1) proteins are degraded to ammonia, peptides, and isoacids
				(2) isoacids may be limiting to growth of rumen microbes depending on rate of carbohydrate fermentation
				(3) ammonia is important for microbial growth and efficiency of carbohydrate fermentation
					(a) ammonia may be derived from NPN sources in the diet
				(4) production of microbial protein important for supply of amino acids to the cow with digestion in small intestine
				(5) protein supply to the cow is from undegraded feed protein, microbial protein, and digestion of endogenous proteins
					(a) microbial protein has a biological value of 66 to 87%
			iii. fat/lipid
				(1) rumen microbes rapidly modify dietary lipids
					(a) hydrolysis of triglycerides
						(i) glycerol and galactose fermented
					(b) biohydrogenation of unsaturated fatty acids
				(2) rumen microbes cannot ferment fatty acids
					(a) they can incorporate lipids into cells
	4. Feeding ruminants
		learn more about feeds in dairy rations
		a. can utilize a wide variety of feedstuffs
		b. important issues
			i. particle size
			ii. structural and nonstructural carbohydrate in ration
				(1) forage to concentrate proportions
			iii. protein fractions
				(1) rumen degradable and undegradable protein in ration
				(2) soluble protein proportion of CP
			iv. Lipid sources
				(1) Types of fats in ration
		c. Water availability

C. Additional Resources