Male

Male Reproductive System

Includes the reproductive organs of Dogs, Cats, Pigs, and Stallions

Testes

Primary male gonads responsible for Gametogenesis by meiosis and Steroidogenesis mainly producing Testosterone

Regulation of Testes

Controlled by Pituitary Gonadotropins, FSH and LH, released in a Pulsatile manner

Gametogenesis

Production of Sperm through Meiosis

Steroidogenesis

Production of Steroid Hormones, mainly Testosterone

Effects of Noxious Agents on Spermatogenesis

Cause Seminiferous Epithelium Degeneration, ↓ Sperm Count, Abnormal Sperm Morphology, and Genetic Defects leading to embryonic or fetal death or Teratogenesis

Radiation Sensitivity of Testicular Cells

Most sensitive to least sensitive is Spermatids, Spermatozoa, then Spermatogonia, while Sertoli Cells are relatively resistant

Seasonal Effects on Spermatogenesis

Breeding season increases Fertility and Ejaculate Quality, influenced by Photoperiod, FSH, LH, and Testosterone, while Hot Weather decreases semen quality

Scrotal Temperature Requirement

Normal spermatogenesis requires Scrotal Testes maintained 2–4°C Below Body Temperature

Bilateral Cryptorchidism

Causes Sterility

Unilateral Cryptorchidism

Causes ↓ Testicular and Epididymal Weight with Impaired Spermatogenesis

Effects of Heat on Testes

Causes Sperm Degeneration and Impaired Spermatogenesis

Testicular Thermoregulation

Maintained by the Scrotum, Tunica Dartos, Cremaster Muscle, Pampiniform Plexus, and Spermatic Artery

Temperature Response of Testes

In Hot conditions testes descend, in Cold conditions testes elevate

Effects of Poor Nutrition on Reproduction

Causes ↓ Libido, ↓ Ejaculate Volume, Poor Semen Quality, and Seminiferous Degeneration

Vitamin A Deficiency

Causes Testicular Atrophy, Poor Semen Quality, Delayed Puberty, and Accessory Gland Hypoplasia

Other Nutritional Causes of Poor Fertility

Include Mineral Deficiencies, Phytoestrogens, Goitrogens, and Nitrates

Hormonal Effects on Spermatogenesis

Estrogen delays seminiferous and accessory gland development, Progestins inhibit LH causing ↓ Spermatogenesis

Fetal Testicular Steroids

Produce Testosterone and Androstenedione

Functions of Fetal Testicular Steroids

Promote Male Genital Development, Accessory Sex Gland Development, Regression of Müllerian Ducts, and Secondary Sexual Characteristics

Special Secondary Sexual Characteristics

Structures used for Attraction, Display, and Combat, such as Bird Plumage and Deer Antlers

General Secondary Sexual Characteristics

Include greater Muscle Mass and Skeletal Size

Functions of Androgens

Maintain Male Secondary Sexual Characteristics, support Spermatogenesis, provide high Testosterone for the germinal epithelium, and regulate Leydig Cell Testosterone Secretion

Functions of Sertoli Cells

Produce Gonadocrinin, GnRH-Like Peptide, regulate testosterone, increase Calcium Permeability of Leydig cells, produce Androgen-Binding Protein, Inhibin, and Estrogen

Androgen-Binding Protein ABP

Binds Testosterone to maintain high intratubular testosterone concentration

Leydig Cells

Produce Testosterone, stimulated by LH ICSH, enhanced by FSH and Prolactin, and are the only testicular cells capable of synthesizing testosterone from Cholesterol

Role of Prolactin in Males

Increases LH Receptor Number, LH Receptor Affinity, and Testosterone Secretion in Leydig Cells

LH Action on Leydig Cells

Activates Adenyl Cyclase, Protein Kinases, RNA Synthesis, and converts Cholesterol → Pregnenolone → Testosterone

Requirements for Normal Spermatogenesis

Require interaction of Germinal Epithelium, Leydig Cells, Sertoli Cells, and Pituitary Gonadotropins, with only minor contribution from Adrenal Androgens

Puberty

Beginning of reproductive capability, depends on the Hypothalamus, Pituitary, Gonads, Target Organ Maturation, Nutrition, and Environment

Leydig Cells During Puberty

Become functional before Sperm Production

Sexual Maturity

Represents full reproductive capacity and follows Puberty → Adolescence → Sexual Maturity

Factors Affecting Hormone Levels

Include Age, Season, Time of Day, and Circadian Rhythm

Androgenic and Anabolic Effects

Cause Masculinization and Muscle Growth

Body Effects of Testosterone

Produce Larger Body Size, Greater Muscle Mass, and Aggressive Mating Behavior

Effect of Excess Body Fat on Fertility

Fat around the scrotum insulates the testes causing ↓ Fertility and ↓ Semen Quality

Other Testosterone-Dependent Characteristics

Influence Hair Growth, Hair Pigmentation, and Feather Pigmentation, producing darker and coarser male hair

Testes-Pituitary Relationship

Aging causes ↓ Leydig Cell Function, while Testosterone provides negative feedback to decrease LH and FSH

Inhibin

Produced by Sertoli Cells, found in Testicular Fluid, Seminal Plasma, and Ovarian Follicular Fluid, decreases FSH with little or no effect on LH

Special Sex Characteristics

Include Hair Color, Horns, Vocalization, Urination Behavior, and Pheromones, all dependent on Gonadal Steroids

Boar Pheromones

During sexual excitement testes release androgenic steroids converted by the Salivary Glands into 5α-Androsterone-Type Steroids bound to Pheromaxein, mainly Androstenol, stimulating estrous sows

Boar Taint

Caused by Androstene Steroids stored in fat, producing a Urine-Like Odor in cooked pork, eliminated by Orchiectomy

Factors Affecting Leydig Cells

Include Cryptorchidism and Restricted Diet

Testicular Estrogens

Produced in Stallions, Bulls, Boars, Dogs, and Humans by Sertoli Cells, stimulated by FSH, through Aromatase conversion of Testosterone → Estradiol

Stallion Estrogens

Produce large amounts of urinary Estrone, small amounts of Estradiol, and no detectable Estriol

Excurrent Tract

Flow is Seminiferous Tubules → Rete Testis → Efferent Ducts → Epididymis → Vas Deferens → Urethra

Rete Testis

Network connecting the Seminiferous Tubules to the Efferent Ducts

Efferent Ducts

Connect the Rete Testis to the Epididymis

Parts of the Epididymis

Consists of the Head Caput, Body Corpus, and Tail Cauda

Spermateliosis Spermiogenesis

Transformation of Spermatids into Spermatozoa before Spermiation

Spermiation

Release of mature Spermatozoa from Sertoli Cells into the seminiferous tubule lumen

Epididymal Maturation

Occurs between the Rete Testis and Cauda Epididymis, where sperm undergo functional maturation

Functions of the Epididymis

Responsible for Sperm Transport, Sperm Maturation, Sperm Protection, and Sperm Storage

Main Sperm Storage Site

The Cauda Epididymis

Source of Ejaculated Sperm

In Humans, Dogs, Cats, and Stallions, most ejaculated sperm come from the Cauda Epididymis and Vas Deferens