Basic Reproduction &

Steve Pritchard UNL Extension Educator Boone-Nance Counties Hormonal Regulation of the Estrous Cycle  Several regulate the estrous cycle  Changes in the concentrations regulate  Recruitment and growth of follicular waves  Timing of ovulation  Length of estrous cycle Reproductive Hormones

 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 to destroy the CL Reproductive Hormones

 Estrogen  acts upon brain to cause the to show heat (estrus)  also prepares uterus for events associated with  Progesterone  acts upon uterus to prepare for pregnancy  acts on brain to prevent heat (estrus) Female Reproduction  Prior to , a heifer’s ovaries fill to 100,000 to 250,000 eggs, number she will have for her lifetime Female Reproductive Tract

Uterus Cervix

Ovary Blind pouch Bladder

Uterine Horns Oviduct (Isthmus, ampulla, infundibulum) Estrous Cycle in Factors Influencing Female Reproduction  Age  Calving difficulty  Bull Reproductive Tract

 Gonads – testicles  & semen transport – epididymis, vas deferens, urethra,  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 . • FSH promotes their Bull Reproductive Tract Factors Influencing Male Reproduction  Bull age  Nutritional intake  Season of the year  Temperature Genetic Terminology

 basic unit of heredity   the genetic make-up of the  Phenotype  the expression of genetic traits (visual) Genetic Terminology

 Heterozygous  a gene pair with different 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 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 and the average performance of all progeny in the 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



67% Heterosis Three Breed Rotation


Ax- 86% Sx-



Gestation Periods

 Beef  282 days + or - 10 days