ANSC 4395 exam 3 QUESTIONS
AND ANSWERS GRADED A
Course
ANSC 4395
Question 1 — Reproductive Physiology
Describe the hormonal regulation of the estrous cycle in a cow. Explain the roles of the
hypothalamus, pituitary, and ovary, and how feedback mechanisms coordinate follicular
development and luteolysis.
Model A Answer:
In the bovine estrous cycle, hormonal regulation begins in the hypothalamus, which secretes
GnRH (gonadotropin-releasing hormone) in a pulsatile manner. GnRH stimulates the anterior
pituitary to release FSH (follicle-stimulating hormone) and LH (luteinizing hormone). FSH
promotes follicular growth, whereas LH supports follicular maturation and triggers ovulation.
Developing follicles produce estradiol, which at low to moderate concentrations exerts negative
feedback on GnRH and gonadotropins to regulate FSH/LH secretion. As follicles mature, rising
estradiol crosses a threshold and triggers a positive feedback surge of LH from the pituitary,
leading to ovulation.
After ovulation, the corpus luteum (CL) forms and secretes progesterone, which maintains
pregnancy if fertilization occurs, and exerts negative feedback on GnRH secretion to prevent
new follicular waves. If no pregnancy is established, the uterus produces prostaglandin F2α
(PGF2α), which causes luteolysis of the CL, a decline in progesterone, and allows the cycle to
restart with new follicular recruitment. This coordinated interplay of hypothalamus, pituitary,
ovarian hormones, and uterine signals ensures cyclicity and reproductive readiness.
Question 2 — Nutrition & Metabolism
Discuss the importance of protein quality and amino acid balance in swine diets. Why is
lysine often considered the first limiting amino acid, and how does imbalance affect growth
and nitrogen excretion?
Model A Answer:
In swine nutrition, protein quality refers to the amino acid profile and digestibility relative to
the animal’s requirements. Pigs cannot synthesize essential amino acids and rely on dietary
sources. Lysine is typically the first limiting amino acid because it is required in higher
proportion for lean tissue accretion and is often the least abundant in cereal-based diets. If lysine
is deficient, protein synthesis is restricted even if total crude protein is high; excess other amino
acids cannot be effectively used, reducing growth efficiency.
, An imbalanced amino acid profile leads to inefficient nitrogen utilization. Unused amino acids
are deaminated, the ammonia produced must be detoxified to urea in the liver, and excreted via
urine, increasing nitrogen excretion to the environment. This not only reduces feed conversion
efficiency but also contributes to ammonia emissions and environmental concerns in
production systems. Formulating diets with balanced essential amino acids using crystalline
supplements improves growth performance, reduces feed costs, and minimizes nitrogen waste.
Question 3 — Genetics & Breeding
Explain the concept of estimated breeding value (EBV) and how it is used in animal
selection. Include a discussion of heritability and accuracy of prediction in your answer.
Model A Answer:
An Estimated Breeding Value (EBV) predicts an animal’s genetic merit for a trait, expressed as
the expected value of an animal’s progeny relative to a population mean. EBVs are calculated
using phenotypic records, pedigree data, and increasingly genomic information. They allow
producers to select animals that will transmit favorable alleles to offspring, improving traits like
growth rate, milk yield, or fertility over generations.
Heritability (h²) quantifies the proportion of phenotypic variation attributable to additive genetic
variance. High heritability indicates that differences among animals are largely due to genetics
rather than environment, making selection more effective. The accuracy of an EBV reflects how
closely the EBV predicts true genetic merit, influenced by the amount and quality of data: the
more records, closer relatives, and genomic markers available, the higher the accuracy. Using
EBVs in selection helps achieve genetic progress efficiently, but it requires understanding the
trait’s genetic architecture and managing correlated responses to selection.
Question 4 — Animal Health
Describe the pathogenesis, clinical signs, and control measures for bovine respiratory
disease complex (BRDC) in feedlot cattle.
Model A Answer:
Bovine Respiratory Disease Complex (BRDC) is multifactorial, involving environmental
stressors, viral pathogens (e.g., IBR, BVDV, PI3, BRSV), and bacterial agents like Mannheimia
haemolytica. Stressors such as weaning, transport, commingling, and dust impair the respiratory
defenses (mucociliary clearance, alveolar macrophages), enabling viruses to infect respiratory
epithelium and predispose to secondary bacterial infection. M. haemolytica produces leukotoxin
and endotoxin triggering inflammation, alveolar damage, fibrinous pneumonia, and pleuritis.
AND ANSWERS GRADED A
Course
ANSC 4395
Question 1 — Reproductive Physiology
Describe the hormonal regulation of the estrous cycle in a cow. Explain the roles of the
hypothalamus, pituitary, and ovary, and how feedback mechanisms coordinate follicular
development and luteolysis.
Model A Answer:
In the bovine estrous cycle, hormonal regulation begins in the hypothalamus, which secretes
GnRH (gonadotropin-releasing hormone) in a pulsatile manner. GnRH stimulates the anterior
pituitary to release FSH (follicle-stimulating hormone) and LH (luteinizing hormone). FSH
promotes follicular growth, whereas LH supports follicular maturation and triggers ovulation.
Developing follicles produce estradiol, which at low to moderate concentrations exerts negative
feedback on GnRH and gonadotropins to regulate FSH/LH secretion. As follicles mature, rising
estradiol crosses a threshold and triggers a positive feedback surge of LH from the pituitary,
leading to ovulation.
After ovulation, the corpus luteum (CL) forms and secretes progesterone, which maintains
pregnancy if fertilization occurs, and exerts negative feedback on GnRH secretion to prevent
new follicular waves. If no pregnancy is established, the uterus produces prostaglandin F2α
(PGF2α), which causes luteolysis of the CL, a decline in progesterone, and allows the cycle to
restart with new follicular recruitment. This coordinated interplay of hypothalamus, pituitary,
ovarian hormones, and uterine signals ensures cyclicity and reproductive readiness.
Question 2 — Nutrition & Metabolism
Discuss the importance of protein quality and amino acid balance in swine diets. Why is
lysine often considered the first limiting amino acid, and how does imbalance affect growth
and nitrogen excretion?
Model A Answer:
In swine nutrition, protein quality refers to the amino acid profile and digestibility relative to
the animal’s requirements. Pigs cannot synthesize essential amino acids and rely on dietary
sources. Lysine is typically the first limiting amino acid because it is required in higher
proportion for lean tissue accretion and is often the least abundant in cereal-based diets. If lysine
is deficient, protein synthesis is restricted even if total crude protein is high; excess other amino
acids cannot be effectively used, reducing growth efficiency.
, An imbalanced amino acid profile leads to inefficient nitrogen utilization. Unused amino acids
are deaminated, the ammonia produced must be detoxified to urea in the liver, and excreted via
urine, increasing nitrogen excretion to the environment. This not only reduces feed conversion
efficiency but also contributes to ammonia emissions and environmental concerns in
production systems. Formulating diets with balanced essential amino acids using crystalline
supplements improves growth performance, reduces feed costs, and minimizes nitrogen waste.
Question 3 — Genetics & Breeding
Explain the concept of estimated breeding value (EBV) and how it is used in animal
selection. Include a discussion of heritability and accuracy of prediction in your answer.
Model A Answer:
An Estimated Breeding Value (EBV) predicts an animal’s genetic merit for a trait, expressed as
the expected value of an animal’s progeny relative to a population mean. EBVs are calculated
using phenotypic records, pedigree data, and increasingly genomic information. They allow
producers to select animals that will transmit favorable alleles to offspring, improving traits like
growth rate, milk yield, or fertility over generations.
Heritability (h²) quantifies the proportion of phenotypic variation attributable to additive genetic
variance. High heritability indicates that differences among animals are largely due to genetics
rather than environment, making selection more effective. The accuracy of an EBV reflects how
closely the EBV predicts true genetic merit, influenced by the amount and quality of data: the
more records, closer relatives, and genomic markers available, the higher the accuracy. Using
EBVs in selection helps achieve genetic progress efficiently, but it requires understanding the
trait’s genetic architecture and managing correlated responses to selection.
Question 4 — Animal Health
Describe the pathogenesis, clinical signs, and control measures for bovine respiratory
disease complex (BRDC) in feedlot cattle.
Model A Answer:
Bovine Respiratory Disease Complex (BRDC) is multifactorial, involving environmental
stressors, viral pathogens (e.g., IBR, BVDV, PI3, BRSV), and bacterial agents like Mannheimia
haemolytica. Stressors such as weaning, transport, commingling, and dust impair the respiratory
defenses (mucociliary clearance, alveolar macrophages), enabling viruses to infect respiratory
epithelium and predispose to secondary bacterial infection. M. haemolytica produces leukotoxin
and endotoxin triggering inflammation, alveolar damage, fibrinous pneumonia, and pleuritis.
