If you are a Cal Poly student enrolled in AVS 303, then these notescover
every subject that will be (possibly) be covered on the final examination.
Do not memorize (you won't be able to), try to understand overall concepts
and relationships as much as possible. Make sure you are familarwith the
calculations we have covered in class, particularly those covered most
recently. These notes are a little cryptic (since I wrote themto lecture
from, not publish), but you should be able to use them to fill in anygaps
in your own class notes (assuming you took any). :-)
If you are NOT enrolled in AVS 303, and are just cruising the websitefor
some obscure reason, you're welcome to do so as well. :-)
Good luck!
Objectives:
1. Understand principles of nutrition, digestive physiology of livestock
species and essential nutrients
2. Familiarity with available feedstuffs, their individual advantagesand
shortcomings
3. Practical aspects of feeding livestock
Goal of the nutritionist:
1. Provide safe, nutritious food supply for people (in food animalspecies)
2. Minimize costs/maximize profits for the livestock producer
3. Support health and production level of the individual animal
Feeding represents largest cost of livestock production - 50-75%, therefore
optimal nutrition program can mean the difference between profit andloss
for producer.
How has this changed over the years?
1. As result of genetics, better nutrition and more intensivemanagement
practices, production has increased dramatically. Example: (referto
handout)
Another example in 1965, avg milk production was 8,500 lb/cow/year;in 1994
avg 15,700 lbs
Genetics of not only livestock, but feedstuffs as well.
Example, through hybrids and selective propagation, alfalfa is higherin
crude protein, lower in fiber and higher in digestibility. Rapeseedhas
such a lower content of goitrogenic compounds that the new and improvedcrop
is referred to by a different name, canola.
GI TRACT
Purpose of the GI tract of every species is to convert the nutrients
contained in feedstuffs into a form that can be absorbed and utlizedby the
body.
This conversion process has two phases: digestion and absorption
Digestion is the breakdown of feedstuffs into absorbable form. Depending on
the species, digestion includes processes such as
mastication (includes cud-chewing)
chemical actions, such as HCl in the stomach
glandular secretions such as enzymes to cleave bonds
microbial action to ferment and digest cellulose
Absorption is the process by which nutrients pass across the cellularlining
of the GI tract into the bloodstream for transport to various tissuesin the
body. Absorption may be either passive (higher to lower conc'n)or actively
pumped into cells.
Variations among GI tracts of species are related to the type of dietthey
consume.
Herbivores eat plant material
Carnivores eat other animals (includes subcategories such as the facultative
carnivore or strict carnivore)
Omnivores eat both
Other categories such as insectivores or frugivores, but not in domestic
animal species
When animals are classified according to their digestive physiology,they
are classified as:
Monogastric vs. ruminants
Monogastric: carnivore, omnivore, herbivore (nonruminant)
Monogastric herbivorous and omnivorous GI system:
Digestive tract starts with the mouth in all species
Process of digestion begins with mastication or chewing
- depending on species, begins to grind food
- mix with saliva
moisten food, help form into bolus
lubricates mouth, aids in taste mechanisms
carrier for buffers and digestive enzymes, primarily amylaseto begin
breakdown of starches
- not every species chews food, example birds swallow food whole, beakis
used to reduce food size in lieu of chewing
- carnivores chew relatively little; teeth adapted for holding andtearing,
molars adapted for crushing bone, not chewing.
Esophagus - cartilagenous tube to transport food from the mouth to the
stomach. Cartilage is surrounded by muscular lining, controlledby CNS. In
some species, transport only occurs in one direction, ie horses whichare
incapable of regurgitation or vomiting. In most species, transportcan
occur in emergency situations, in some species, reverse transport hasbeen
adapted. Example, ruminants will regurgitate boluses of foodfor more
chewing (rumination), other example wild canines will transport meatin
their stomachs, then regurgitate it for their young when back at theden.
Stomach - first point at which significant species differences occur.
Stomach sometimes referred to as glandular stomach because lined with
secretory cells producing substances involved with the digestive process:
Proportion of the different types of secretory tissues varies withspecies,
according to the type of diet consumed
Four primary areas of the stomach:
1. Nonglandular - no secretory tissues
2. Cardiac region - lined with epithelial cells, secrete mucin
Mucin - substance which lines stomach and protects the wallsfrom being
digested
3. Fundic region - three types of calls;
parietal cells, secrete Hcl
neck chief cells, secrete mucin
body chief cells, secrete pepsinogen, rennin, lipase
pepsinogen - in presence of Hcl –> pepsin, a protease
rennin - milk curdling, found only in young animals, used incheese-making
lipases - cleaves bonds in fats
4. Pyloric region - more neck chief and body chief cells.
SMALL INTESTINE
After food has been ground up, mixed with saliva and gastric secretions,it
is referred to as chyme.
SI primary site for enzymatic digestion, consists of three parts:
duodenum, jejunum, ileum (note different spelling from "ilium", whichis
part of the pelvic structure)
Duodenum: pH neutralized from pH 2-2.5 in stomach to 6.8-7 by bile produced
by liver. Bile is stored in gall bladder (horses and dolphinshave no gall
bladder, continuous secretion only) and released when food is presentin
duodenum. Bile also emulsifies fat. Secretions from pancreasand lining of
the duodenum contain additional enzymes to digest nutrients.
Jejunum and ileum are primary sites for absorption of simple carbohydrates,
minerals, fats and proteins.
LARGE INTESTINE
Consists of cecum, colon and rectum. Relative size dependent onspecies and
type of diet consumed—horses and rabbits have large cecum, while swineand
poultry much smaller. Site of microbial digestion.
Animals do not have ability to digest fiber, microbes do (enzymes tocleave
beta bonds in cellulose)
Microbial population consists of primarily bacteria, protozoa, yeasts-
Thousands of species and strains, billions of total cells. By-products
secreted by bugs - digestive enzymes, B vitamins, K vitamin, VFAs (lactic,
acetic, propionic, butyric, others to lesser extent). Also synthesize
non-essential amino acids.
Absorption of these nutrients occurs in cecum and colon, but limited
absorption of vitamins and proteins. In some species (rats andrabbits), to
avoid loss of nutrients, practice coprophagy to recycle nutrients,eliminate
need for some vitamins. Koalas have used same strategy to weanbabies from
milk onto solid diet, excrete semi-digested paste of eucalyptus leaveswhich
is high in nutritive value to young.
Absorption of water occurs throughtout GI tract but primarily in colon,
amount varies among spp.
AVIAN SPECIES
Monogastric spp. Differences, stomach is replaced by crop, proventriculus
and gizzard.
Crop not present in fish or insect-eating spp, temporary storage site.
Proventriculus acts like simple stomach - gastric secretions produced
Gizzard - tough muscular lining, grit, grinds up food, replacementfor
chewing.
Relatively long SI, two ceca, very short colon. Urine and fecescombined
before excretion.
RUMINANTS
The primary difference in digestive anatomy/physiology between ruminantsand
non-ruminants is that the site for microbial fermentation occurs beforethe
small intestine, rather than after as in the non-ruminant. Implicationsfor
ability/efficiency of absorbing certain nutrients.
In non ruminants, the GI tract is arranged stomach, SI, cecum, LI -
fermentation occurs in cecum and colon
In ruminants, stomach, SI, LI, fermentation occurs in stomach (4-chambered)
Let's look at physiology, then discuss the differences this makes
Ruminant stomach is divided into four chambers:
1) reticulum
2) rumen
3) omasum
4) abomasum
The omasum is not essential to the ruminant - we know this because
pseudoruminants (camelids) do not have an omasum and do just fine.
The rumen is considered the first part of the stomach - forage entersrumen
first, concentrates enter reticulum first. The actual openingfrom the
esophagus to reitculorumen is cardia. The rumen does NOT secreteany
substances, but is lined with papillae to increase surface area formore
efficient absorption. The rumen is also lined with muscles thatcontract
rhythmically to mix ingesta to maximize microbial action and fermentation.
By-product of fermentation in rumen is carbon dioxide and methane, mustbe
eliminated or animal will bloat, process = eructation. Matureanimal 1.2 -
2 L gas/min continuously. If foam forms in rumen (sometimes occursafter
alfalfa or high concentrate diet), gas cannot escape, accumulates inrumen,
if not relieved, animal can die. One of the functions of salivain the
ruminant is to decrease surface tension, enable gas to escape moreeasily.
You put more contaminants into the air by driving 3 blocks than a 1000lb
ruminant will its entire life, thus cattle's effect on "greenhouseeffect"
is minimal.
Microbial action occurs in both rumen and reticulum, with free flowof
ingesta between the two. Approximately 800 species, vary withtype of diet,
region and between individuals. Typical concentration is 25-80billion/ml
of rumen fluid. Products of microbial action are same in ruminantas in
monogastric (VFAs, water-soluble vitamins, enzymes, ammonia, and microbial
proteins, which are absorbed across rumen and reticulum wall into
bloodstream.
Rumination originates from the reticulum - large particles of food are
regurgitated, re-chewed, further mixed with saliva, re-swallowed. Ruminants
produce large amts of saliva (100-120 liters/day in 1000 lb animal).
Monogastric spp can survive w/o salivary glands, ruminants cannot. Lg amts
of sodium bicarbonate which acts as a buffer—if reticulorumen pH getstoo
low (too acid), microbes start to die off, decreases activity. This is
also where N and minerals (primarily Na, K, inorganic P and Cl) arerecycled
in ruminants.
- Monogastric excrete excess nitrogen, ruminants recycle and utilizeto
build microbial proteins.
After rumination, ingesta travels to omasum.
60-70% of water entering is absorbed, ~ 100L/d
Also VFAs (mostly absorbed in rumen)
Omasum has leaf-like projections that increase SA
Abomasum (true stomach)
Folds to slow passage of ingesta and increase secreting SA
Only portion that secretes (others absorb only) - same secretions asin
momogastric spp
Differences - secretion is continuous, not in response to a meal asin S-S,
as in ruminants, food is always present.
Enzymes not as powerful, lower concentration (not necessary)
In young ruminants, esophageal groove, extends from cardia to omasum(by
passing rumen and reticulum) Presence of milk closes groove to directmilk
directly into omasum and abomasum. When the calf/lamb startsto eat forage
and grain, the groove opens and allows ingesta to move into rumen for
microbial fermentation, but not fully functional until 8-9 weeks. Until
then, young ruminants are essentially a simple-stomached spp. Eventually
ability to close this groove is lost by age of ~ 2 years in cattle.
How does the different digestive physiology affect the animal?
Ability to digest and utilize poorer quality feeds and still converta
high-fiber forage diet into body tissue. Rumen much more efficientat
digesting fiber than is the cecum/colon.
Part of reason is relative size of rumen: in adult animal, ~80% of thetotal
digestive tract is rumen
Allows for food to remain longer, move more slowly through system,take
15-21 for food to move completely through ruminant GI tract; vs. ~18 hr in
a monogastric spp.
Microbes in rumen also have ability to utilize lower forms of protein,ie
urea and ammonia and to recycle N. This means that the dependenceon
high-quality proteins, ie SBM are less than in monogastric, which affects
economics.
Disadvantages to ruminant digestive physiology:
1) 8-10% of the energy in a feed will be lost through methane and cannotbe
utilized by animal
2) Microbes degrade protein and rebuild. If your protein sourcewas poor
(ie urea), that's an advantage. If producer is feeding high quality
protein, ie SBM, then this rebuilding nets no benefit, but still resultsin
loss of energy. So more efficient to feed cattle low qualityprotein than
high quality protein. However, microbes cannot convert low qualityprotein
fast enough to supply needs of high-producing dairy cow, so you MUSTfeed at
least some high quality protein and just live with the energy loss.
3) Less efficient than monogastric spp at utilizing good-quality forages.
Can utilize lower quality feeds very well, but feed conversion is abouthalf
of smonogastric spp.
4) Ruminants do not utilize fats well. Fats are most energy densefeed
available, but fats disrupt microbial population. In monogastric,fats are
absorbed before they reach site of fermentation (cecum). In ruminants,site
of fermentation occurs before SI. Feed companies attempting toencapsulate
fat droplet with cellulose coating so that fat is not released untilafter
leaves rumen.