Download Animal Growth and Development oVERVIEW INSTRUCTOR: UNIT

Animal Growth and Development
OVERVIEW
INSTRUCTOR:
UNIT:
Performance of Technical Skills Related to Animal Science and Technology
LESSON:
Explaining Animal Growth and Development
IMS REFERENCE: #8391
LESSON PLAN
LESSON OBJECTIVES
The student will be able to:
 discuss processes and periods of growth;
 recognize effects of hormones on growth;
 relate the importance of nutrition to growth;
 identify hereditary mechanisms affecting growth; and
 explain the aging process in animals.
KEY TERMS
 adipocytes
 amino acids
 anabolism
 chondrocytes
 cleavage
 dam
 degradation
 deoxyribonucleic acid
 differentiate
 dystocia
 endocrine system
 fertilization
 fertilized
 gametes
 gastrulation
 genes
 genotype
 germ layers
 gestation
 heritability
 homeostasis
 hyperinsulinemia
 intermuscular
 intramuscular
 intra-abdominal
 malnutrition
 metabolism
 mitotic division
 myoblasts
 myotube
 neural
 ovum
 phenotype
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Animal Growth and Development
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primitive gut
progeny
proteolysis
puberty
pubescent
resorption
respiration
spermatozoon
subcutaneous
synthesis
triglyceride
zygote
SUPPLEMENTAL MATERIALS & RESOURCES
 IMS #8391
 Class Notes for IMS #8391
 Lesson Test for IMS #8391
 PowerPoint Presentation for IMS #8391
TEACHING PROCEDURES
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PREPARATION
Key Points
Link:
Methods
Discuss how growth and development of
humans is similar to that of animals. What is
the same?
Different?
How is the aging
process the same? Different?
Motivation:
Challenge students
to determine what
animal(s) have the same gestation period as
humans.
Overview:
Student Thought and
Reflection
Student
Challenge/Class
Discussion
Review of Objectives
In this lesson, the students will:
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discuss processes and periods of growth;
recognize effects of hormones on growth;
relate the importance of nutrition to growth;
identify hereditary mechanisms affecting growth;
and
 explain the aging process in animals.
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PRESENTATION
Key Points
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Methods
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Animal Growth and Development
INTRODUCTION
PowerPoint Slides #2-10
Growth and development have important
implications for domestic animal production;
significantly influence value of animal being
produced
Agricultural research focuses on how to make
animal growth and development processes
efficient; research involves several disciplines;
animal growth, development are controlled by
genes, hormones
Growth and development are continuous,
dynamic processes requiring integration of
numerous physiological functions influenced
by:
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nutrition
efficiency of metabolism and respiration
hormonal regulation
immune responses
physiological status
diseases and parasites
maintenance of homeostasis
Pre-natal: processes occurring before birth or
hatching
Post-natal: processes occurring after birth or
hatching
Ovum or egg: single cell from which an animal
originates
Sperm: (spermatozoan) fertilizes ovum or
egg; released by male
Zygote: result of egg fertilization by sperm;
develops in enclosed environment (uterus or
egg)
Gestation: (incubation period) period of time
zygote develops in uterus or egg
Gestation periods:
Cattle: approx. 283 days
Sheep: approx. 150 days
Swine: approx. 112 days
Chicken egg: 21 days
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Animal Growth and Development
After birth, young animals experience a period
of rapid growth and development until
maturity; After maturity, some processes (i.e.
bone elongation) stop; others slow down (i.e.
muscle deposition).
Genetics determine maximum animal size;
nutrition, disease influence animal reaching
genetic potential for size
PRE-NATAL GROWTH AND DEVELOPMENT
PowerPoint Slides #11-33
Embryogenesis
 extends from the union of female, male
gametes to the emergence of the
embryonic axis
 zygote: single cell repeatedly cleaved to
form a multi-celled ball known as morula
 morula: becomes blastula and then
gastrula; same size as original zygote;
blastomeres: numerous cells that make up
morula
 cleavage: process involves mitotic division
of original cell into two cells, which then
divide into four cells, then into eight cells;
continues until cells of developing embryo
are reduced to size of cells in adult animal
 number of cells double in stages of
cleavage; individual cells do not grow or
enlarge in size
 cells of morula are rearranged to form a
hollow sphere filled with fluid; embryo is
referred to as a blastula; fluid-filled space
inside sphere is called blastocoel
 Gastrulation: process in which blastula
becomes gastrula; involves extensive
rearrangement of blastomeres
 until gastrulation, cell division has occurred
but blastomeres (cells) have not increased
in size
 cells on one side of the blastula move
inward and form two-layered embryo;
layers are ectoderm (outer layer),
endoderm (inner layer); mesoderm third
cell layer: formed between the ectoderm
and endoderm
 cavity forms in gastrula known as primitive
gut; later develops into animal’s digestive
system
 all tissues and organs form from one of
three layers of cells in gastrula; After the
germ layers establish, cells rearrange,
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Animal Growth and Development
develop into tissues and organs
Organogenesis
 cells grown and differentiate during this
phase
 process extends from neurela stage to birth
 neurela stage: differentiation; when
unspecialized embryonic cells change into
specialized cells destined to form specific
tissues or organs; starts at upper surface of
gastrula
Display Table 1 in PowerPoint Presentation
 Cells of the ectoderm divide and form the
neural plate
 Neural tube: formed by two raised edges or
neural folds appearing and gradually
coming together
 Neural crest: mast of cells pinched off top
of neural tube; migrates to other parts of
embryo to give rise to neural and other
structures
 Front part of the neural tube thickens,
forms the brain; remainder of tube
becomes spinal cord
 after conception, cells differentiate into
organs and body structures; embryo is then
referred to as a fetus; body structures
continue to grow and develop until birth
 Horses: embryo referred to as fetus at
about 40 days following conception;
humans: 56 days to develop fetus
 Body tissues, organs formed in specific
sequence:
1. head is formed before tail
2. spinal cord formed before other organ
 Highly differentiated cells (brain, nerve),
cannot be replaced if destroyed after
original number is fixed during fetal stage;
nerve cells seriously damaged thereafter
are not replaced, usually remain
permanently damaged
 Muscle cell numbers fixed during fetal
stage; can only increase in size, not in
number
 Bone (skeletal size) can be increased by
environmental conditions; not beyond the
genetic potential of animal
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PowerPoint Slides #3436
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Animal Growth and Development
POST-NATAL GROWTH
Post-natal growth extends from birth until
death; length of this period depends on
species;
Average life span:
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mouse: 2 years
humans, elephants: over 60 years
Sheep: 15 years
cattle: 30 years
Main types of tissues that develop as animal
grows
 muscle
 bone
 fat
Rate of deposition depends on age of animal;
type of tissue being deposited
PowerPoint Slides #3739
Muscle
Myoblasts: muscle fibers formed from multiple
cells; in prenatal stage, myoblasts fuse
together to form myotube (develops into
muscle fiber)
One muscle fiber has multiple nuclei; postnatal
growth of muscle characterized by increases in
length, diameter
Muscle fibers: predominantly protein, size is
determined by the rate of protein synthesis
minus the rate of degradation;
deoxyribonucleic acid (DNA) content of muscle
cells increases as animal develops
PowerPoint Slides #4041
Bone
Bone tissue: grows before and after birth
Ossification: hardening of cartilage at each
end; bone grows in length; after cartilage on
ends of a bone has completely hardened, bone
stops growing
Bones capable of increasing in width, can
repair themselves if broken
Although individual bones reach a mature
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Animal Growth and Development
length and stop elongating, bone tissue is
constantly being deposited and reabsorbed
PowerPoint Slides #4246
Fat
Fat tissue: comprised of fat cells and
connective tissue; two types:
 white fat: stores energy
 brown fat: maintains constant body temp.
Fat cells: increase or decrease in size
depending on nutritional status of the animal
Fat deposited in four different areas:
 Intra-abdominal: deposited in abdominal
cavity around kidneys and pelvic area; first
fat deposited
 Subcutaneous fat: (backfat) deposited
under skin; usually largest amount of fat
deposited
 Intermuscular fat: deposited between
muscles of animals
 Intramuscular fat: fat deposited within
muscle
o level deposited is referred to as degree
of marbling; affects quality, taste of
meat
o determines quality grade of beef carcass
in U.S.
o manipulation of process important in
meat production systems
o last type of fat to be deposited; animals
with high degrees of marbling have large
amounts of fat deposited in other areas
of carcass
PowerPoint Slides #4753
Muscle, bone, fat deposited differently
throughout the animal’s life
 Bone elongation stops after animal reaches
mature body size; bone tissue deposition,
reabsorption continue until animal dies
 Muscle tissue develops between birth and
maturity; muscle growth then slows down,
not physiologically halted
 Fat deposition occurs after bulk of muscle
has been deposited; misconception that fat
is only deposited in middle aged or mature
animals; significant amount of fat is
deposited in young; because protein
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Animal Growth and Development
deposition declines markedly with age,
fattening is more apparent in mature
animals; rate of deposition, amount of fat
deposited depends on diet of animal; young
animals receiving an overabundance of milk
or nutrients become fat
Growth occurs quickly during early stages of
animal’s life; After puberty, bone elongation
stops, skeletal size does not increase; live
weight continues to increase
Puberty occurs:
Cattle: 10 months of age
Sheep: 6 months of age
Swine: 5 months of age
PowerPoint Slides #5469
HORMONAL CONTROL
Hormones: regulate deposition of different
tissues and partitioning of energy for various
processes involved in growth, development
Important hormones involved in growth and
development:
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insulin
growth hormone
Insulin-like Growth Factor 1 (IGF-1)
thyroid hormones
glucocorticoids
sex steroids
Insulin:
 important hormone involved in muscle
growth, development
 stimulates transport of certain amino acids
into muscle tissue
 active in reducing rate of protein
degradation
 key hormone in regulation of food intake,
nutrient storage, nutrient partitioning
Growth hormone:
 stimulates protein anabolism in many
tissues; reflects increased amino acid
uptake, increased protein synthesis,
decreased oxidation of proteins
 enhances utilization of fat by stimulating
triglyceride breakdown, oxidation in
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Animal Growth and Development
adipocytes
 seems to have a direct effect on bone
growth by stimulating the differentiation of
chondrocytes
 maintain blood glucose within a normal
range; said to have anti-insulin activity;
suppresses ability of insulin to stimulate
uptake of glucose in peripheral tissues;
enhances glucose synthesis in liver
 administration of growth hormone
stimulates insulin secretion, leading to
hyperinsulinemia; major role of growth
hormone in stimulating body growth is to
stimulate the liver and other tissues to
secrete IGF-1
IGF-1:
 Stimulates proliferation of chondrocytes
(cartilage cells) resulting in bone growth;
important in protein, fat, carbohydrate
metabolism; stimulates differentiation,
proliferation of myoblasts and the amino
acid uptake and protein synthesis in muscle
and other tissues
Thyroid hormone:
 Required for normal growth
 Deficiencies of T4 or thyroxine and T3
(Triiodothyronine) cause reduced growth as
a result of decreased muscle synthesis and
increased proteolysis
 Alterations in thyroid associated with
changes in the ribonucleic acid
(RNA)/protein ratio in skeletal muscle
 important influence on the prenatal
development of muscle
Glucocorticoids
 restrict growth, induce muscle wasting
 effect metabolic rate, energy balance
 Androgens (male sex hormones) have
obvious effect on muscle development,
growth
 Estrogens (female sex hormones)
significant roles in maximizing growth;
thought to act indirectly through effects on
secretion of other hormones
 Androgens-direct effect because of
androgen receptors located on muscle cells
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Animal Growth and Development
HOMEOSTASIS
Homeostasis: concept closely integrated with
growth and development of an animal.
 normal growth patterns affected if
homeostasis is not maintained at all times
 concept refers to maintenance of an
internal equilibrium
 Many processes and functions (voluntary
and involuntary) contribute to maintaining
this state of internal balance, controlled by
nervous system (nervous regulation) and
endocrine system (chemical regulation)
 maintained at all levels, from individual
cells to the whole animal; i.e. cells must
maintain suitable salt and water levels
while tissues and organs require specific
blood glucose levels
 Maintaining requires a high level of
interaction between hormonal and nervous
activities.
 Example: maintenance of a constant
internal temperature; temperature must be
kept within a certain range for an animal to
remain alive, grow, function normally
 animal is becoming increasingly hot moving
from an open area to shaded area is
voluntary action; may involuntarily start to
sweat; dissipates heat, not controlled by
animal; occurs in response to internal
stimuli
PowerPoint Slides #78106
GENETIC CONTROL
 processes involved in growth, development
occurring at cellular level
 can be difficult to control or manipulate
processes
 managers of livestock systems manipulate
growth, development to optimize
production
 knowledge of cellular level activity must be
applied to cellular level activities of whole
animal
 important factor in management because
genetic composition determines potential
for growth, development
 animals have set genotype to determine
potential for growth
 phenotype affected by environmental
factors: nutrition, disease, parasites,
injuries
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Animal Growth and Development
 traits are heritable from parents; some
more than others: genotype expressed
more strongly, environment less influential
for some traits
 genes code for different traits, some
influenced by multiple genes; rate of
growth influenced by genes controlling
appetite, tissue deposition, skeletal
development, energy expenditures, body
composition
 genes add together to produce measurable
traits
Refer to Table 2 for heritability of growthrelated traits
 Genetic potential for prenatal growth
inhibited by environmental factors; i.e.
chickens limited by egg size because of
amount of nutrients available to developing
chick; birth weight may be affected by size
of litter, available uterine space, supply of
nutrients
 Embryos from small parent have been
transplanted into larger parent resulting in
birth weights greater than non-transplanted
contemporaries
 Growth from birth to weaning affected by
amount of milk produced by dam
 Swine studies indicate that up to 20% of
growth during period controlled by
heritability; 35-50% of weaning weight
affected by milking ability of dam, litter
size, environmental factors
 Cattle and sheep: growth during period
strongly related to genetic ability, with
heritability ranging from 20-30%
 During period, genetic potential for growth
can be evaluated, provided nutritional
levels are adequate with disease and
parasites controlled
 Mature size selection has developed large
and small strains of chickens, rabbits,
swine, cattle, sheep; mature size related to
gain and feed efficiency
 Large, late maturing animals growing when
market weights reached; carrying less fat,
waste
 Larger framed animals suitable for lean
meat markets
 High-yield carcass producers rewarded
financially
 Small, early maturing animals have finished
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Animal Growth and Development
growth, higher proportions of fat; good for
market where marbling is desired
 Breeding genetic manipulation is long-term
commitment; producers need to consider
long-term market objectives, opportunities
Texas and US: cattle production focused on
feedlot to produce meat for domestic
consumption
Cattle produce high-yielding carcasses with
sufficient marbling, have high feed efficiencies,
most valuable
All levels: focus on producing beef of
acceptable quality
Australia: cattle are grass-fed until two-three
years of age; results in leaner, larger
carcasses destined for export to Asian
countries (Japan, Philippines); emphasis
placed on growth rates in male animals,
calving percentages in females
Survival: major factor due to harsh
environmental conditions; tick resistance, heat
tolerance are important traits
PowerPoint Slides #107131
Selection for increased growth rates will result
in larger framed animals; negative result due
to decreased marbling, feed efficiency,
increased feed costs, higher birth weights,
higher rates of dystocia; led producers to
consider feed efficiency more suitable trait
THE INFLUENCE OF EXTERNAL FACTORS
 Diet and environmental conditions must be
optimal or favorable for genetic potential to
be reached for growth, fattening, milk
production, egg laying, other
developmental processes
 Nutrition: controllable short-term variable
for producers; animal requires certain level
for normal development, functioning of
body systems-referred to as maintenance
requirements; affects all stages of growth
and development
 Optimal growth of muscle and fat require
additional nutrients
 Poor nutrition results: stunted growth,
malformed organs, disease, brittle
skeletons, susceptibility to parasites, poor
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Animal Growth and Development
reproductive performance; lead to reduced
income
 Operations spend much time and money to
provide optimal nutrition for animals
 Intensive livestock systems: feed costs
contribute more than 80% of total costs
 Nutrition affects growth at all stages
o dam’s nutrition during gestation and
lactation effects offspring’s development;
poor nutrition lead to low birth weights,
heavy death losses in newborn
 Species differ: sheep and cattle partition as
many nutrients as possible into fetus; use
own reserves to meet deficiencies (iron);
some species abort fetus if nutritional
status falls below certain level
 Effects of poor nutrition after birth on
postnatal growth and ultimate mature size
depends on:
o age at which poor nutrition occurs
o length of time subjected to poor nutrition
o kind of poor nutrition
 Long-term effects: poor nutrition as young
calf never reaches genetic potential to
marble, structural development continues if
period is short
 Poor nutrition benefit: compensatory
growth (phenomenon identified in animals
that go through short period of malnutrition
then return to adequate nutrition
 Weight loss, slowed development with poor
nutrition; as improves, starts to utilize
nutrients efficiently, thus weight gain
occurs quickly and efficiently
 Nutrition used to manipulate growth
patterns; high energy diets fed in finishing
phase to encourage marbling; strategies
used based on desired end-product, age of
turn-off, available feed sources
 Disease negatively impacts growth and
development; sickness requires
repartitioned nutrients, causes reductions in
intake; long-term effects impair animal’s
ability to harvest, digest, absorb nutrients
causing long-term impairment of growth,
development
 Effects of parasites varies from mild to
severe; can be as drastic as death; internal
and external parasites decrease appetite
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Animal Growth and Development
therefore intake of food, depress wool
production, inhibit digestive functions,
cause permanent internal tissue damage,
make animal physically sick
 Prevent and combat with treatments
145
THE AGING PROCESS IN ANIMALS
 Aging: series of changes in animals that
lead to physical deterioration, eventually
death
 Species reaches peak of productive life; i.e.
maximum egg laying highest during hen’s
first year of production, swine max litter
size occurs at 3-4 years of age
 Animal is born, it begins to die: true in
physiological sense; after formation of
embryo, cells of certain tissues stop
dividing; cell division stops in other tissues
until only tissues essential to maintenance
of life continue to divide
 Longevity roughly proportional to length of
time required for animal to reach maturity;
rabbits reach maturity in 6 months, life
expectancy of four years; cattle require 2-3
years mature, have life expectancy of 2025 years
 Physiological function deteriorate with age;
reproductive organs secrete lower levels of
hormones, decline of muscular strength and
speed of motion; time required for body
substance imbalances becomes longer with
age; collagen (proteins in skin), blood
vessels become less elastic with age,
wrinkles from, vessels collapse or burst
 Increased breakdown of neural and
glandular control
 Reproductive and lactating abilities of
female decrease with age
 Sows: inefficient producer earlier because
excessive sizes create higher body
maintenance requirements resulting in
injuries to baby pigs; frequently culled by 3
years of age
 Cows culled 10 to 11 years
 Ewes culled 7 to 8 years
 Genetic, environmental factors affect life
span of animals; longevity is heritable trait
estimated by knowing life span of
individual’s parents and siblings
 Life span decreased if animal is required to
produce at higher than normal levels for
substantial period of time (common in dairy
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Animal Growth and Development
cows)
 Inadequate or excessive nutrition hastens
aging process
 Higher environmental temperatures shorten
life expectancy
 Sex: females usually outlive males
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APPLICATION
Key Points
Methods
Working in groups, have students research the
growth and development of 10 different
animal species. Using the internet or the
library, have students find the following
information on each species:
Group
Research/Presentatio
n
 Length of gestation or incubation period
 When animal is considered a fetus as
opposed to an embryo
 Age at puberty
 Life expectancy
 Average age at which animal is sold if
animal is commercially produced
Each group should create a chart displaying
information and present information to the
class.

EVALUATION/ SUMMARY
Key Points
Methods
Complete Lesson Test for IMS #8391
Worksheet
REFERENCES/ ADDITIONAL MATIERIALS
Bone Growth and Development. [Online]. Available:
http://georgia.ncl.ac.uk/VitaminD/BoneGD.html [2001, June].
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Animal Growth and Development
Boorman, K. N., P. J. Buttery, and D. B. Lindsay. The Control of Fat and Lean
Deposition. Oxford, UK: Butterworth and Heinmann, 1992.
Gilbert, S. F. Developmental Biology. 6th ed. Sunderland, MS: Sinauer Associates
Inc., 2000.
Heritability in Cattle. [Online] Available:
http://muextension.missouri.edu/xplor/agguides/ansci/g02910.htm [2001,
June]
Homeostasis in Animals. [Online]. Available:
http://bioserve.latrobe.edu.au/vcebiol/cat1/aos2/u3aos22.html [2001, June]
Rook, J. A. F. and P. C. Thomas. Nutritional Physiology of Farm Animals. New York,
NY: Longman Inc., 1983.
Schraer, W. D. and H. J. Stoltze. Biology: The Study of Life. 4th ed. Needham, MS:
Prentice-Hall Inc., 1991.
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