ANSC growth&development

growth

“true growth” is a net increase in body protein

(fat, bone, and water are omitted from this)

measuring growth in lay terms

growth = W2 - W1/ T2 - T1

Weight per day

WDA = weight per day of age; include birth weight

WDA = 1,150/442 = 2.60 lb (total weight/age)

are higher or lower ADG’s and WDA’s more desirable?

generally higher is better

it is more profitable

who profits from compensatory gain?

cow/calf producer —→ running yearlings manager ——> feedlot operator ——> slaughterer

hyperplasia

increase in the number of cells

almost all hyperplasia occurs prenatally

hypertrophy

an increase in cell size

postnatal growth is all hypertrophy

growth exceptions

are animals, like rodents, that are much less developed at birth than are farm animal babies

periods or phases of growth

prenatal - before birth

postnatal - after birth

pre-weaning - still getting mothers milk

post weaning - fending for self

smaller young at birth result

being in a larger litter - less space and nutrients

a smaller uterus - less space to grow

s smaller mother - less uterine space

a younger mother - she is still growing

inadequate nutrition for the mother

weight at weaning is affected by:

milk production of dam

gene potential for growth

pasture amount and quality

age of the dam

sex of animal

castration

creep feed

diet

calf weaning weight of cow

peaks at cow age of 6 years with little difference at 5, 6, and 7

mainly is a milk yield effect

post weaning gain 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

external - nutrition and environment

internal - genes and hormones

hormones

secretions of endocrine (ductless) glands that are carried in the blood to sites where they are used

Ex: adrenaline - the fight or flight hormone

primary endocrine glands of the sheep

pituitary gland

growth hormone - somatotropin

from anterior pituitary

stimulates N retention; protein goes up

affects cho and fat metabolism

too much —→ acromegaly (giantism)

too little ——> dwarfism

hypothyroidism

too little - causes out “motors” to run too slowly

too much - causes out motors to run too fast. “Pop-eyed” condition

estrogens

from ovaries and adrenal glands (small amount)

androgens

from testes and adrenal glands (small amount)

increase growth; decrease fattening

(steers are taller than bulls)

tissue weight in beef cattle

heifers fatten faster than steers and steers faster than bulls

tissue weight in swine

barrows are fatter than gilts

what happens at maturity?

• less muscle growth

• fattening

• no more increase in height

• slowing of daily gain

• decrease in body functions and metabolic rate

number of eggs in hens

hens lay the most eggs the first year and steadily decline each year thereafter

senescence

getting old (decline)