Driver's a G - Growth

Sigmoidal Growth Curve:

shaped like an “S” - shows the cumulative weight of the animal over time

Sigmoidal growth curves are actually ______ _________.

stair stepped

Why are sigmoidal growth curves stairstepped?

growth occurs in spurts due to the sporadic nature of growth

What can impact growth in an animal?

• environment

• disease or health state

• nutritional intake

• hormone function

What are the 3 segments of the sigmoidal growth curve?

1. Self-accelerating

2. Point of Inflection

3. Self-inhibiting

Self-Accelerating Phase:

characterized by exponential but non-complex growth that occurs in the early stages of development

Why does growth begin to slow as it nears the point of inflection?

• Harder to supply the rapidly dividing cells with nutrients, oxygen, and blood

• Harder to get rid of cellular waste products

Point of Inflection:

period of greatest average daily gain - occurs during puberty in most species

After the point of inflection, growth continues at a __________ rate.

decreasing

Why does growth slow during the self-inhibiting phase?

the animal is reaching its mature size and nutrient intake is nearing maintenance requirement

What hormone secreted by the hypothalamus reduces growth?

somatostatin (GHIH)

Asymptote:

the point at which food intake reaches the maintenance requirement - animal has hit its mature body weight

Chronological Age:

age in absolute time units (days, months, years)

What factors can change an animals chronological growth curve?

nutrition, disease, stress, and activity level

Physiological Age:

the specific physical or chemical stages of maturity (height, weight, composition, puberty)

How do chronological and physiological age relate?

animals of different species will reach different physiological levels of maturity at different chronological time points

Cumulative Growth Curve:

plots the animals total weight over time - usually a sigmoidal “S” shaped curve

What is one weakness of using a cumulative growth curve?

hard to identify the period of maximum growth (point of inflection)

Absolute Growth Curve:

plots the gain per unit of time against time - ADG per week, month, etc.

What is one weakness of absolute growth curves?

the growth rate changes as the animal grows - only accurate if the time intervals are short

Relative Growth Curve:

plots growth in relation to total weight - growth rate per unit of weight plotted against time

As an animal grows, its relative growth rate ________.

decreases

What type of growth curve is #1?

Cumulative

What type of growth curve is #2?

Absolute

What type of growth curve is #3?

Relative

What were John Hammonds two important observations?

1. Body components that are physiologically more important develop first

2. Extremities complete their development first

How did John Hammond study compositional growth changes?

animals were raised under typical conditions of environment or nutrition OR were raised in malnourished conditions

Allometric Growth:

the study of how body parts change in size as an animal develops - the study of body proportions

Who first described allometric growth?

Julian Huxley

How did Huxley come up with the allometric growth theory?

studied how the fighting claw of fiddler crabs grew in relation to whole body growth

What is the basic allometric growth equation?

Y = ax^b

A _______ relationship exists between growth of each __________ and the whole body.

constant; tissue/organ

How does allometric growth apply to muscle development?

different muscles develop faster or slower depending on the species

Isometric tissues/organs develop…

at the same rate as the whole body (b=1)

Hammond proved that which tissue doesn’t follow the allometric growth theory?

adipose tissue

Which tissues recieve first “dibs” on the nutrients in the blood stream?

• Brain and central nervous system

• Placenta and fetus in pregnant females

Which tissue gets last “dibs” on nutrients in the blood stream?

adipose/fat tissue

In the forumla y=ax^b, Y stands for:

log weight of a carcass or animal

In the forumla y=ax^b, A stands for:

constant weight of tissue or component

In the forumla y=ax^b, B stands for:

growth coefficient of tissue or component - indicates the slope of the line

(B > 1) =

tissue or component is growing at a faster rate and has a high growth impetus (late developing tissue)

(B = 1) =

tissue or component is growing at a similar rate to the whole with an average growth impetus (isometric growth)

(B < 1) =

tissue or component is growing at a slower rate and has a low growth impetus (early developing tissue)

How does the maximum growth rate differ among tissue?

different tissues reach max growth rate at different times during development (bone > muscle > fat)

How can composition of growth be measured using absolute growth curves?

the cumulative weight of muscle, bone, and fat over time indicates which tissues are growing in relation to the overall weight of the animaland how their proportions change throughout development.

How can composition of growth be measured on a percentage basis?

by analyzing the percentage of each tissue type relative to total body weight at various stages of development - adds up to 100% at any given time point

Fat becomes a _______ proportion of the body with age.

larger

Muscle and bone makeup a _______ proportion of the body with age.

smaller

Water and protein make up a ________ portion of the body with age.

smaller

Water content of muscle, fat, and bone is greatest ______ in life and _________ with age.

early; decreases

Where is most extra fat stored in the body?

subcutaneous and mesenteric fat stores

What is the order in which adipose stores reach maturity? (which ones fill first)

kidney > mesenteric > subcutaneous > intermuscular > intramuscular

Does the # of adipocytes increase with age?

NO - amount of fat accumulation in each adipocyte does

Mineral content in bone ________ with age.

increases (ossification of cartilage)

The absolute amount of ___________ _______ increases with age.

connective tissue

As muscle atrophies, the _______ of connective tissue increases, but the ________ amount stays the same. This is known as the ________ ________.

percentage; absolute; dilution effect

Phenotype = _________ x __________

genotype; environment

Species:

organisms capable of interbreeding and producing fertile offspring

Breed:

subsets of organisms within a species that have the same chromosome #, but differing genetic codes, traits, behaviors, etc.

Heredity:

the process of passing along genes from one generation to the next

Evolution:

the gradual change in species over time through natural selection and adaptation, leading to the diversification of life and the emergence of new species

Genotype:

the unique set of genes that an animal possess in its genome

Heritability:

the ability of an animal to pass a particular trait to the next generation

H > 0.5 = a ______ heritable trait

highly

0.2 < H < 0.5 = a ______ heritable trait

moderately

H < 0.2 = a ______ heritable trait

lowly

Selection and domestication has caused a change in the ________ __________ of muscle.

relative distribution

How do wild ruminants differ in muscle distribution compared to domestic ones?

have a greater % of muscle located in the upper portions of the hind legs - enhances speed and agility to escape predators

How has muscle distribution changed in domesticated ruminants?

greater % of muscle in abdominal muscles to support their extensive rumens and in front legs to bear weight associated with grazing for long periods of time

Where do pigs have increased muscle deposition?

around the spinal column - supports rooting behavior

Cattle and sheep favor ___________ and ___________ fat depos.

intermuscular and subcutaneous

Swine favor __________ fat depos.

subcutaneous

Poultry have ______ _________ fat depos.

evenly distributed (between kidney, intermusuclar, subcutaneous) to support flight

What were cattle domesticated from and when?

Aurochs around 8500 BC

Where was Bos Taurus domesticated?

the fertile crescent

Where were Bos Indicus domesticated?

India

What was the first trait selected for in domesticated cattle?

docility

What are the two types of cattle with regards to skeletal size?

large-framed (Continental) and small-framed (British)

How many frame scores are there in cattle?

7

What is the purpose of assigning a frame score?

To categorize cattle based on skeletal size and growth potential - aids in breeding and management decisions

Frame score is determined using…

Age + Hip Height

Large framed cattle reach a heavier weight at a given…

chronological age

Large-framed cattle take ______ to reach physiological maturity compared small-framed cattle.

longer

At the same chronological age, how do large- and small-framed cattle compare?

Large-framed will be physiologically more immature (leaner) because they are later-maturing animals - have more growing to do overall

When compared at the same physiological age, small- and large-framed cattle are…

compositionally equivalent (muscle:fat ratio is the same)

In cattle, how does selection for muscle impact milk production?

selection for muscle is inversely related to milk production - meat breeds are poor milk producers

How have muscle fibers been affected in milk breeds (cattle)?

selection for milk production caused a reduction in muscle fiber #’s that occurs prenatally (during gestation development)

How has muscle distribution changed in milk breeds?

it hasn’t - only the size (# of fibers) in each muscle group

How is wool selection related to muscle in sheep?

selection for wool production is inversely related to muscle growth - wool breeds vs. meat breeds

Which has the larger frame size, wool or meat breeds? (sheep)

Wool breeds

How does muscle selection impact reproduction in swine?

inverse relationship - terminal and maternal breeds

Describe growth in intact males:

• capable of large mature body weights than castrates or females

• attain compositional maturity at a later chronological age than castrates or females

• usually heavier at a given chronological age

Why do intact males grow larger and faster than castrates and females?

boost from testosterone production - nutrient partioner

How does muscle deposition differ in intact males?

have more muscle located in the forequarter (neck + thorax) - associated with secondary sex characteristics

Why do males and females differ in muscle depsotion?

have higher levels of estrogen or testosterone receptors in different muscle groups which encourages more growth in those groups

How does muscle distribution differ in females?

have a greater proportion of muscle in the pelvic limbs and abdominal wall - associated with secondary sex characteristics

How does muscle deposition differ in castrates?

have a more uniform muscle deposition throughout the body than females or intact males

Males have larger ________ ________ _________ than females or castrates.

muscle fiber diameter

Why are females smaller in frame size than intact males and castrates?

estrogen stimulates closure of the epiphyseal plates (growth plates) and suppresses chrondocytes which results in a smaller frame and earlier physiological maturity

Why do males have thicker bone diameter than females?

testosterone better stimulates periosteal bone growth