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
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