Animal Genetics, EPDs, and Male Reproductive Anatomy

Vocabulary flashcards covering livestock genetic evaluation, EPD interpretation, and male reproductive anatomy and physiology based on the lecture notes.

Heritability ($h^2$)

A score that estimates the proportion of phenotypic variation attributable to genetics; higher values provide greater confidence that traits (such as marbling or ribeye area) will be passed on to offspring.

Expected Progeny Difference (EPD)

A genetic evaluation metric calculated by breed associations that estimates the expected performance difference of an animal's future offspring compared to the breed average.

Accuracy (EPD)

A statistical measure indicating the degree of confidence in an animal's EPD value based on recorded performance data, which guides how many females a producer should breed to that sire.

Inbreeding Depression

A reduction in fitness and performance, most noticeably affecting reproductive efficiency, caused by intensive linebreeding and the expression of homozygous recessive traits.

Weaning Weight

An EPD trait that reflects pre-weaning calf growth, which is heavily influenced by maternal care and the mother's milk production.

Yearling Weight

An EPD trait indicating post-weaning growth rate up to harvest age, reflecting the animal's own genetic potential rather than maternal environmental influence.

Maternal Weaning Weight

A combined genetic evaluation index that accounts for both the calf's direct growth genetics and the genetic contribution of the dam's milk production.

Sigmoid Flexure

An S-shaped anatomical bend in the fibroelastic penis of bulls, rams, and billy goats that straightens out to allow penile extension during copulation.

Retractor Penis Muscle

A smooth muscle attached near the sigmoid flexure that relaxes to allow penile extension during breeding and contracts to draw the penis back into the sheath.

Fibroelastic Penis

A type of penis composed of dense, rigid connective tissue found in farm ruminants and boars that relies on the relaxation of retractor muscles rather than blood engorgement for extension.

Filiform Appendage

A small, thread-like tube extending from the glans penis in rams and billy goats designed to spray semen evenly across the female's cervix.

Spermatogenesis

The biological process of producing sperm cells, requiring approximately $60$ days from initial cell division until mature sperm reach the cauda epididymis.

Pampiniform Plexus

A complex network of testicular veins coiled around the testicular artery that functions as a countercurrent heat exchanger to cool blood before it reaches the testes.

Cremaster Muscle

A muscle that raises and lowers the testes relative to the body wall to regulate testicular temperature in response to environmental heat or cold.

Tunica Albuginea

The dense, white fibrous connective tissue capsule that surrounds and holds together the internal structures of the testicle or ovary.

Seminiferous Tubules

The highly convoluted microscopic tubules within the testes where sperm cells are generated by Sertoli cells.

Rete Testis

A network of internal tubules that collects immature sperm from the seminiferous tubules and transports them toward the epididymis.

Cauda Epididymis

The tail section of the epididymis that serves as the final storage and maturation reservoir where sperm cells are both motile and fertile.

Caput Epididymis

The head section of the epididymis where newly arrived sperm cells exhibit motility but have not yet achieved fertility.

Vas Deferens

The muscular duct that transports mature sperm cells from the epididymis toward the urethra for ejaculation.

Leydig Cells

Interstitial endocrine cells located between the seminiferous tubules in the testes that synthesize and secrete testosterone.

Sertoli Cells

Somatic cells located within the seminiferous tubules that nurture developing germ cells and produce sperm cells.

Scrotal Circumference

A physical measurement of testicular size in breeding males that serves as an indicator of sperm-producing capability and correlates with earlier puberty onset in female offspring.