Basic Reproduction & Genetics Steve Pritchard UNL Extension Educator Boone-Nance Counties Hormonal Regulation of the Estrous Cycle Several hormones regulate the estrous cycle Changes in the concentrations regulate Recruitment and growth of follicular waves Timing of ovulation Length of estrous cycle Reproductive Hormones hormone a chemical substance secreted by a gland hypothalamus part of brain, secretes GnRH pituitary pituitary small gland produces follicle stimulating hormone (FSH) produces luteinizing hormone (LH) Reproductive Hormones FSH causes follicle to grow on ovary stimulates follicle to secrete estrogen LH acts on mature follicle to cause ovulation and formation of corpus luteum (CL) Ovulation occurs 24-32 hrs after standing heat causes CL to secrete progesterone Reproductive Hormones Prostaglandin F2α Uterus releases when no pregnancy to destroy the CL Reproductive Hormones Estrogen acts upon brain to cause the female to show heat (estrus) also prepares uterus for events associated with mating Progesterone acts upon uterus to prepare for pregnancy acts on brain to prevent heat (estrus) Female Reproduction Prior to birth, a heifer’s ovaries fill to 100,000 to 250,000 eggs, number she will have for her lifetime Female Reproductive Tract Uterus Cervix Vagina Vulva Ovary Blind pouch Bladder Uterine Horns Oviduct (Isthmus, ampulla, infundibulum) Estrous Cycle in Beef Factors Influencing Female Reproduction Age Calving difficulty Nutrition Bull Reproductive Tract Gonads – testicles Sperm & semen transport structures – epididymis, vas deferens, urethra, penis Accessory glands – seminal vesicles, Cowper’s gland, prostate (add fluid volume and nutrients) Bull Reproductive Tract Age of Bull Circumference (cm) 12-14 months 33 15-20 35 21-30 36 >30 37 Reproductive Hormones Testicle functions produce sperm produce testosterone • causes development and maintenance of the secondary sex characteristics • increases muscular and skeletal growth • behavior in males • reproductive tract development and maintenance Reproductive Hormones Seminiferous tubules contains Leydig and Sertoli cells • Leydig cells produce testosterone under the influence of LH • Sertoli cells are nurse cells for sperm, providing nutrients and energy. • FSH promotes their function Bull Reproductive Tract Factors Influencing Male Reproduction Bull age Nutritional intake Season of the year Temperature Genetic Terminology Gene basic unit of heredity Genotype the genetic make-up of the animal Phenotype the expression of genetic traits (visual) Genetic Terminology Heterozygous a gene pair with different genes for the same trait Homozygous a gene pair where both genes are identical Genetic Terminology MPPA (Most Probable Producing Ability) an estimate of a cow’s future productivity for a trait based on her past productivity Weaning weight ratio compares an individual to the average of the group which it was raised (same sex, same calf crop- called a contemporary group). A ratio of 100 is average. Genetic Terminology Heterosis the increase in performance associated with the crossbred animal when compared to the average of the purebred parents Expected Progeny Difference (EPD) is the difference between the average performance of the individual’s offspring and the average performance of all progeny in the population Heritability The proportion of trait variation due to additive genetics Ex. - yearling wt. 35% heritable 35% due to genetics 65% due to environmental factors Heritability & Heterosis Inverse relationship Trait Heritability reproduction low production moderate carcass high Crossbreeding Programs Two Breed Rotation H A AH HA 67% Heterosis Three Breed Rotation H A Ax- 86% Sx- S Hx- Gestation Periods Beef 282 days + or - 10 days.