Animal Growth and Development

1. AG-ASB-14 The student describes the physiological processes involved in prenatal and postnatal growth and development of agricultural animals. a. Measures the growth process in an animal. b. Analyzes the circumstances of growth that affect production enterprises. c. Distinguishes between prenatal and postnatal growth and illustrates the phases of each. d. Explains the layers of the blastula and the organs that are derived from each layer. e. Describes the functions of the placenta. f. Identifies characteristics of twenty-four, forty-eight, and seventy-two hour old chick embryos. g. Differentiates between body cells and explains the functions of each type cell. h. Sequences fat deposition in an animal’s body. i. Investigates and explains why selection for muscling in animals is important. j. Compares and contrasts the growth and reproductive phases in an animal’s life. k. Describes the effects of hormones in the growth process. l. Describes the effects castration has on the growth of an animal. m. Explains the aging process in animals. n. Distinguishes between chronological and physiological age. Animal Growth and Development

2. Measures the growth process in an animal/ Analyzes the circumstances of growth that affect production enterprises. • All animals experience a growth process in order to develop from a fertilized egg to a mature adult • Animal producers make their living based on the amount of growth an animal experiences • Paid by weight- More weight gain = more $$ • Growth- defined as an increase in the size or volume of living matter • Hyperplasia- increase in the number of cells • Hypertrophy- increase in the size of cells

3. Distinguishes between prenatal and postnatal growth and illustrates the phases of each. • Prenatal- takes place before the animal is born • 3 phases- ovum, embryonic, fetal • Ovum phase- fertilization of the egg until the mass of cells attaches to the wall of the uterus • Lasts about 10 days in sheep and 11 days in cattle • Little change takes place and the shape stays spherical (morula) • Cell division occurs through cell mitosis • As cells mass continues to grow, a fluid-filled cavity develops in the center of the cells (blastula)

4. Embryonic phase/ Explains the layers of the blastula and the organs that are derived from each layer/ Describes the functions of the placenta. • major tissues, organs, and their major systems are differentiated • Lasts from 10d-34d in sheep and 11d-45d in cattle • Embryo attaches to the uterus and sac like pouch develops around the embryo (placenta with amniotic fluid) • feeds the embryo and give oxygen and dispose of wastes • Also acts as a shock absorber and to protect fetus • The fetus changes but does not gain much weight • Step 1: Blastula’s divides into three layers- ectoderm (outer), mesoderm (middle) and endoderm (inner) • Morphogenesis- cell development into different tissues and organs • Step 2: Ectoderm develops into the tissues on the outside or near the surface of the animal’s body • skin, hair, hooves and certain glands • Also forms the central nervous system (brain, spinal cord, nerve branches) • Step 3: Mesoderm develops into skeletal and muscular system of animal including bones, muscles, cartilage, tendons and ligaments, heart, veins, arteries, reproductive system • Step 4: Endoderm forms the inner organs like the liver, digestive system, lungs • Animal takes on a recognizable form in the late embryonic stage

5. Fetal Stage • Animal develops all of the organs of the body • Liver, heart, and kidneys develop earlier that digestive tract • Various organs grow faster at times than other organs • When fetus is able to live on its own, oxytocin stimulates the muscles of the uterus to contract causing parturition • Birth canal relaxes and animal is expelled from uterus • Lungs begin functioning when the animal hits the ground

6. Distinguishes postnatal growth and illustrates the phases of each. • The parts of the animal’s body do not grow and develop at the same rate after birth • Tissues develop in the order of most importance to survival • Head- comprises a larger portion of the body at birth than any other time of life • Contains brain that directs all other organ function • Legs- tend to be a larger portion of body at birth than at later stages • Necessary for nursing and get away from predators • Nervous, respiratory and digestive system organs develop early after birth for animal to breath and eat • Drinking colostrum from mother helps develop gut • Animal grow rapidly from birth until sexual maturity • This is the time of greatest growth rate and feed efficiency

7. Differentiates between body cells and explains the functions of each type cell/ Investigates and explains why selection for muscling in animals is important. • Size of animal is dependent on the size and amount of bones and muscles in body • All animal’s muscle cells are in place at birth • Muscle cells are long and relatively thin and contain many nuclei. • Muscle cells grow in size but not in the number of cells. • Bone cells multiply before and after birth • Bones get longer by the hardening of the cartilage tissue at the end of the bones- ossification • Mature bone is made up of ½ minerals (calcium and phosphorus) and ½ protein

8. Sequences fat deposition in an animal’s body. • At sexual maturity, the animal muscle and bone growth slows and then stops and the animal begins to lay down fat layers • Fat is nature’s way of storing energy for the animal to use when it is not getting as much feed as normal • White fat- stores energy • Brown fat- maintains animal’s body heat • Fat deposits first in the abdominal cavity to cushion organs, then between muscles (intermusclar fat) and then inside the muscles (intramuscular fat or marbling)

9. Describes the effects of hormones in the growth process. • Hormones- chemical substances formed by the endocrine glands and secreted into the bloodstream • Stimulate organs into action or control bodily processes • Growth is controlled by hormones • Glands secreting growth hormones- pituitary, thyroid, testicles, ovaries and adrenal • Hormones regulate the ultimate size of the animal • Excessive amount- animal is abnormally large • Too little- dwarf animal • Producer use artificial hormones that are implanted (ear) in the animal to control growth • Closely regulated by FDA

11. Describes the effects castration has on the growth of an animal. • Castration of males slows growth and increases fat deposition • When the testicles are removed, the production of testosterone stops and growth rate is affected • Castration also affects lean-to-fat ratio • Amount of lean versus fat in the body • Females have the lowest lean-to-fat ratio • Intact males (not castrated) have the highest ratio • Castration causes males to add less muscle but more marbling

12. Explains the aging process in animals. • Aging- from the time of birth until death • Involves a series of changes that lead to deterioration of the body and eventually death • Physiological age- stage of maturity the animal has reached • Usually done by examining bones of animal after slaughter • Vertebrate in younger animals have cartilage while older animals have bone • Life expectancy- how long an animal can be expected to live • Sheep- mature in one year, but live about 10 years • Cattle- mature in 2-3 years but can live 20-25 years • Functions of animals decrease with age • Muscular strength and speed decline, reproductive organs begin secreting lower levels of hormones, recovery time takes longer, nerves break down, wrinkles form as collagen and protein become less elastic, animals lose teeth and can’t eat as well • Cows usually culled at 10-11 years, ewes at 7-8 years and sows at 2-3 years