ansc growth
Definition of growth
- “True Growth”- is a net increase in body protein
Fat, bone and water are omitted from this definition because they can be increased or decreased at any time
Typical growth curve
o Isn’t linear-------Typical growth curve is “S” shaped
o A fast-growing animal has a steep curve
o Due to different hormones usually when they’re younger during puberty
o Steep=they grow more in a shorter period of time
o When they’re younger they need more nutrients
o During maturity and animals’ growth slows down and they maintain their weight
o Age reduces palatability, and efficiency
Measuring growth in lay terms
GROWTH=W2-W1/T2-T1
ADG=Average Daily Gain
Example
A steer weighed 800lbs going into the feedlot and 1150 after being fed 120 days
ADG= (1150-800)/120=2.92lb
Measuring growth rate another day
WDA= weight per day of age; includes birth weight
Example
The steer in the feedlot example was 442 days old when it weighed 1150 lbs
WDA=1150/442=2.60lb
Are higher or lower ADGs and WDAs more desirable
· If an animal gains faster
o It goes to the market sooner
· It uses your facilities for a shorter amount of time-less expenses
· More of it gross energy is used fpr production and less maintenance
· IT IS MORE PROFITABLE
· We need to allow the animal to grow and develop
o All this body mass but the skeleton isn’t strong enough to support the weight
How does growth occur
- Hyperplasia-an increase in the number of cells
· Almost all hyperplasia occurs prenatally
- Hypertrophy-increase in cells size (after birth)
§ Occurs postnatally
Periods or phases of growth
- Prenatal-before birth
- Postnatal-after birth
o Preweaning-still getting mother’s milk
o Post weaning- fending for itself
Smaller at birth results:
No toughness when small at birth and limits growth rate for the rest of it life
Factor that can affect size:
- Being in a larger litter- less space and nutrients
- A smaller uterus-l ess space to grow
- A smaller mother- less uterine space
- A young mother- she is still growing
- Inadequate nutrition for the mother
[ Brahman heifers have the ability to shrink the calf size
Brahman bulls are recognized for siring big animals ]
Fetal growth
In which trimester does the most weight growth occur?
- Third trimester
Effects of uterine size in offspring
Maternal size influences the size of the foal
Waight at weaning is affected by:
v Milk production of dam
v Gene potential for growth
- Pasture amount and quality
- Age of dam
- Sex of animal
- Castration
- Creep feed-supplementing the diet of young livestock
- Diet
Calf weaning weight peaks at age of 6 years with little difference in 5, 6, and 7
Post weaning affected by:
- Genetics of the animal
- Amount and kind of feed
- Sex-males>castrates>females-hormones
- Age-greatest gain during puberty
- Climate-can have a LARGE effect
Factors affecting growth
v External-nutrition and environment
v Internal-genes and hormones
Priorities for nutrients in pregnant females
1. Fetus and membranes
2. Nerves
3. Bones
4. Muscles
5. Fat
Level of hormone secretions affects gain and other traits
Hormones-secretions of endocrine(ductless)gland that are carried in the blood to sites where they are used
Not all cells have receptors for all hormones(not all hormones have affects on certain tissues)
Example: Adrenalin- the flight of flight hormone
Growth hormone-somatotropin
- Produced by the anterior pituitary
- Can be made by genetically engineered microbes
- Species specific- medicine must be specified to THAT species
- Stimulates n retention; protein
- Affects Cho and fat metabolism
- Too muchàacromegaly(giantism)
- Too littleà dwarfism
- Barry bonds- baseball player who used growth hormones and grew alot
-
Thyroxin-from thyroid
- Hypothyroidism-too little causes our motors to run too slowly
- Hyperthyroidism-too much; causes our motors too run too fast
Estrogens- from ovaries and adrenal glands(small amounts)
- Close epiphyseal plates (females shorter than males)
- Testosterone and estrogen-muscle growth
- Makes bones grow faster
- Intact makes have longer bone growth earlier in life and eventually stops
- A steer never had the influence of testosterone and slowdowns the bone growth
- But…...converts bone marrow to bone at because they grow for a longer period of time
Androgens- from testes and adrenal glands (small amount)
- Increase growth; decrease fattening
- Steers are taller than bulls
What happens at maturity?
- Less muscle growth
- Fattening
- No more increase in weight
- Slowing of daily gain
- Decrease in body functions and metabolic rate
Senescence-growing old