CONTENTS
PREFACE
ACKNOWLEDGMENTS
CONTRIBUTORS
PART I Functional Anatomy of Reproduction
CHAPTER 1 Anatomy of Male Reproduction
DEVELOPMENT
TESTIS AND SCROTUM
EPIDIDYMIS AND DUCTUS DEFERENS
ACCESSORY GLANDS
PENIS AND PREPUCE
LABORATORY ANIMALS
REFERENCES
SUGGESTED READING
CHAPTER 2 Anatomy of Female Reproduction
EMBRYOLOGY
THE OVARY
THE OVIDUCT
THE UTERUS
CERVIX UTERI
THE VAGINA
EXTERNAL GENITALIA
REFERENCES
PART II Physiology of Reproduction
CHAPTER 3 Hormones, Growth Factors, and Reproduction
ENDOCRINE GLANDS
HORMONES
PRIMARY HORMONES OF REPRODUCTION
CLINICAL USES OF HORMONES
HORMONAL REGULATION OF REPRODUCTION
GROWTH FACTORS
REFERENCES
CHAPTER 4 Reproductive Cycles
PRENATAL AND NEONATAL PHYSIOLOGY
PUBERTY
ESTROUS CYCLES
BREEDING SEASON
AGING AND FERTILITY
REFERENCES
SUGGESTED READING
CHAPTER 5 Folliculogenesis, Egg Maturation, and Ovulation
FOLLICULOGENESIS
ENDOCRINOLOGY OF FOLLICULAR GROWTH AND OVULATION
EGG MATURATION
OVULATION
REFERENCES
SUGGESTED READING
CHAPTER 6 Transport and Survival of Gametes
SPERM TRANSPORT IN THE FEMALE TRACT
RECEPTION OF EGGS (OVA PICKUP)
EGG TRANSPORT IN THE OVIDUCT
FERTILIZABLE LIFE AND AGING OF EGGS
TRANSUTERINE MIGRATION AND LOSS OF EGGS
EMBRYONIC DEVELOPMENT IN OVIDUCT
REFERENCES
SUGGESTED READING
CHAPTER 7 Spermatozoa and Seminal Plasma
SEMEN
SPERM CELLS
SEMINIFEROUS EPITHELIUM
BLOOD-TESTIS BARRIER
EPIDIDYMAL TRANSIT, SPERM MATURATION AND STORAGE
SEMINAL PLASMA
ACCESSORY GLANDS
SPERMATOZOAL METABOLISM
IMMUNOLOGIC ASPECTS OF SPERMATOZOA
IN VITRO EVALUATION OF SEMEN
ASSISTED REPRODUCTIVE TECHNOLOGIES
SUGGESTED READING
CHAPTER 8 Fertilization and Cleavage
FERTILIZATION
CLEAVAGE
EARLY EMBRYONIC DEVELOPMENT
REFERENCES
CHAPTER 9 Implantation
EARLY EMBRYONIC DEVELOPMENT
REFERENCES
CHAPTER 10 Gestation, Prenatal Physiology, and Parturition
GESTATION
MATERNAL PHYSIOLOGY IN PREGNANCY
PLACENTA
FETAL PHYSIOLOGY
PARTURITION
PUERPERIUM
REFERENCES
PART III Reproductive Cycles
CHAPTER 11 Cattle and Buffalo
CATTLE
BUFFALO
REFERENCES
CHAPTER 12 Sheep and Goats
INTRODUCTION
SEXUAL SEASON
PUBERTY
FOLLICULOGENESIS
ESTROUS CYCLE
OVULATION
BREEDING AND CONCEPTION
GESTATION, PARTURITION, AND PUERPERIUM
REPRODUCTIVE PERFORMANCE
SUMMARY
REFERENCES
CHAPTER 13 Pigs
SEXUAL DEVELOPMENT AND MATURATION
HORMONE REGULATION IN THE BOAR
SPERM PRODUCTION
HORMONES AND PUBERTY IN GILTS
CONCEPTION RATE
EMBRYO SURVIVAL
LITTER SIZE
PREGNANCY
POSTPARTUM ESTRUS
LACTATION
SOW AT WEANING
REFERENCES
CHAPTER 14 Horses
BREEDING SEASON
REPRODUCTIVE PARAMETERS IN STALLIONS
ESTROUS CYCLES
GESTATION
FOALING
EQUINE HYBRIDS
REPRODUCTIVE FAILURE IN MARES
REPRODUCTIVE FAILURE IN STALLIONS
CONCLUDING REMARKS
REFERENCES
SUGGESTED READING
CHAPTER 15 Llamas and Alpacas
FEMALE
MALE
REFERENCES
SUGGESTED READING
CHAPTER 16 Reproduction in Poultry: Male and Female
CONTROL OF GAMETE PRODUCTION
REFERENCES
PART IV Reproductive Failure
CHAPTER 17 Reproductive Failure in Females
OVARIAN DYSFUNCTION
DISORDERS OF FERTILIZATION
PREGNANCY WASTAGE
PERINATAL AND NEONATAL MORTALITY
DISORDERS OF GESTATION, PARTURITION, AND PUERPERIUM
REFERENCES
CHAPTER 18 Reproductive Failure in Males
CONGENITAL MALFORMATIONS
EJACULATORY DISTURBANCES
FERTILIZATION FAILURE
NUTRITION AND MALE INFERTILITY
INFERTILITY AND CHROMOSOMAL ABERRATIONS
REFERENCES
PART V Physiopathologic Mechanisms
CHAPTER 19 Reproductive Behavior
SEXUAL BEHAVIOR
MECHANISMS OF SEXUAL BEHAVIOR
FACTORS AFFECTING SEXUAL BEHAVIOR
A TYPICAL SEXUAL BEHAVIOR
MATERNAL AND NEONATAL BEHAVIOR
REFERENCES
SUGGESTED READING
CHAPTER 20 Genetics of Reproductive Failure
BASIC GENETIC CONCEPTS
ABNORMAL KARYOTYPES
GENETICS OF INFERTILITY
MAMMALIAN HYBRIDS
REFERENCES
SUGGESTED READING
CHAPTER 21 Genetic Engineering of Farm Mammals
DEVELOPMENT OF TRANSGENIC ANIMALS
DEFINITIONS
APPLICATIONS OF TRANSGENIC ANIMALS
PRODUCTION OF TRANSGENIC LABORATORY ANIMALS
PRODUCTION OF TRANSGENIC DOMESTIC ANIMALS
ANALYSIS OF GENETIC MANIPULATIONS: TRANSGENES AND OTHER MODIFICATIONS
CONCLUSIONS AND FUTURE DIRECTIONS
REFERENCES
SUGGESTED READING
CHAPTER 22 Pharmacotoxicologic Factors and Reproduction
PLANTS THAT AFFECT MALE REPRODUCTION
PLANTS THAT AFFECT FEMALE REPRODUCTION
MYCOTOXINS AND MALE REPRODUCTION
MYCOTOXINS AND FEMALE REPRODUCTION
MYCOTOXINS AND EMBRYONIC DEATH, FETAL DEATH, AND ABORTION IN LIVESTOCK
AGRICULTURAL PESTICIDES AND MALE REPRODUCTION
AGRICULTURAL PESTICIDES AND FEMALE REPRODUCTION
REFERENCES
CHAPTER 23 Immunology of Reproduction
AN IMMUNOLOGY PRIMER
COMPONENTS OF THE IMMUNE SYSTEM IN THE REPRODUCTIVE TRACT
REGULATION OF CELLULAR IMMUNE FUNCTION IN THE REPRODUCTIVE TRACT
IMMUNOLOGIC IMPLICATIONS OF PREGNANCY
REFERENCES
CHAPTER 24 Molecular Biology of Reproduction
GENETIC DETERMINANTS IN REPRODUCTION
DEVELOPMENT OF THE GONADS
MOLECULAR PARAMETERS OF SPERMATOGENESIS
MOLECULAR PARAMETERS OF OVULATION
FERTILIZATION AND IMPLANTATION
PREGNANCY AND PARTURITION
LACTATION AND MATERNAL BEHAVIOR
REFERENCES
SUGGESTED READING
PART VI Assisted Reproductive Technology
CHAPTER 25 Semen Evaluation
EVALUATION AND FERTILITY
APPEARANCE AND VOLUME
SPERM CONCENTRATION
SPERM MOTILITY
SPERM MORPHOLOGY
SEMEN QUALITY
ANCILLARY TESTS
REFERENCES
CHAPTER 26 Artificial Insemination
MANAGEMENT OF MALES/SEMEN COLLECTION
CATTLE
SWINE
HORSES
SHEEP
REFERENCES
CHAPTER 27 X and Y Chromosome-Bearing Spermatozoa
BIOLOGY OF SPERM
TECHNIQUES OF SPERM SEPARATION
FUTURE RESEARCH
REFERENCES
CHAPTER 28 Pregnancy Diagnosis
IMPORTANCE OF PREGNANCY DIAGNOSIS
CLINICAL METHODS OF PREGNANCY DIAGNOSIS
IMMUNOLOGIC DIAGNOSIS
CONCLUDING REMARKS
REFERENCES
CHAPTER 29 Ovulation Induction, Embryo Production and Transfer
INDUCTION OF OVULATION
SYNCHRONIZATION OF ESTROUS CYCLES
EMBRYO TRANSFER
REFERENCES
SUGGESTED READING
CHAPTER 30 Preservation and Cryopreservation of Gametes and Embryos
PRINCIPLES OF CRYOBIOLOGY
CRYOPRESERVATION OF EMBRYOS
CRYOPRESERVATION OF SEMEN
REFERENCES
SUGGESTED READING
CHAPTER 31 Micromanipulation of Gametes and Embryos: In Vitro Fertilization and Embryo Transfer (IVF/ET)
GENETIC ENGINEERING
MICROMANIPULATION OF GAMETES, EMBRYOS, AND ZONA PELLUCIDA
ZONA PELLUCIDA
GAMETE INTERACTION
INTRACYTOPLASMIC SPERM INJECTION (ICSI)
MOLECULAR ANDROLOGY
INSTRUMENTATION, WATER AND AIR FILTRATION, CULTURE MEDIA
MACROMOLECULAR SUPPLEMENTATION
REFERENCES
SUGGESTED READING
GLOSSARY
GLOSSARY OF COMMON ABBREVIATIONS
UNITS OF MEASURE
APPENDICES
APPENDIX I Chromosome Numbers of Bovinae, Equinae, and Caprinae Species
APPENDIX II Chromosome Numbers and Reproductive Ability in Equine, Bovine, and Caprine Hybrids
APPENDIX III Preparation of Physiologic Solutions
COMPOSITION OF SOME COMMON BUFFERS AND SOLUTIONS
APPENDIX IV Technique for Determining Spermatozoal Concentration Using a Hemacytometer
RECOMMENDED EQUIPMENT
TECHNIQUE
CALCULATION OF SPERM CELL CONCENTRATION
APPENDIX V Preparation of Sperm Stains
PAPANICOLAOU STAINING
STOCK SOLUTIONS
SPECIAL CONSIDERATIONS
APPENDIX VI Preparation of Trypsin for Zona-Free Hamster Ova
APPENDIX VII Evaluation of Chromosomes of Ova
APPENDIX VIII Book/IVF Companies
APPENDIX IX In Vitro Fertilization by Microinjection
INDEX
Editor: Donna Balado
Managing Editor: Karen Gulliver
Marketing Manager: Annie Smith
Production Editor: Paula C. Williams
Copyright © 2000 Lippincott Williams & Wilkins
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First Edition, 1962
Japanese translation, 1965
Spanish translation, 1967
Second Edition, 1968
Japanese translation, 1971
Third Edition, 1974
Fourth Edition, 1980
Reprinted, 1982
Portuguese translation, 1982
Italian translation, 1985
Fifth Edition, 1987
Japanese translation, 1992
Spanish translation, 1992
Sixth Edition, 1993
Library of Congress Cataloging-in-Publication Data
Reproduction in farm animals / edited by B. Hafez, E.S.E. Hafez.—7th ed.
p. cm.
Includes bibliographical references.
ISBN 0-683-30577-8
1. Livestock—Reproduction. 2. Veterinary physiology. I. Hafez, B.
II. Hafez, E. S. E. (Elsayed Saad Eldin), 1922–
SF871.R47 2000
636.089'26—dc21 99-053783
The publishers have made every effort to trace the copyright holders for borrowed material. If they have inadvertently overlooked any, they will be pleased to make the necessary arrangements at the first opportunity.
To purchase additional copies of this book, call our customer service department at (800) 638-3030 or fax orders to (301) 824-7390. International customers should call (301) 714-2324.
04 05 06 07
2 3 4 5 6 7 8 9 10
PREFACE
The first edition, published in 1962, covered the basic and comparative aspects of reproductive physiology in a simplified manner to meet the needs of students in reproductive biology, veterinary medicine, and animal sciences. This objective is maintained in the seventh edition, which represents a condensed, concise treatise on the physiology and biochemistry of reproduction of farm animals. The book is divided into major sections and these, in turn, are loosely arrayed into two domains, the components of the reproductive system and the regulation of the reproductive process, from the control of ovulation to the initiation of parturition. The reader will note the profound differences among the various animal species. To address this issue we provided separate coverage of the major species, where this seemed appropriate, so that the student of reproduction could ascertain the similarities and differences among them.
During the past decade there were significant advances in the main concepts of animal reproduction as a result of modern biotechnology, such as the use of gonadotropin releasing hormones and their analogs, assisted reproductive technology/andrology (ARTA), genetics, molecular biology, immunology, toxicology, and pharmacology. Five new chapters have been added to the 7th edition:
Modern techniques of bioengineering of farm animals involve microinsemination, recombination of DNA, and in vitro manipulation, transfer, and expression of genes. These techniques were greatly improved with the use of computers, microcomputers, and commercially available diagnostic and analytical kits. A wide variety of techniques have been employed for the evaluation of semen, such as: evaluation of sperm fertilizability using zona-free hamster egg (fresh or frozen); motility pattern as viewed by videotape microscopy; in vitro penetrability of sperm in bovine cervical mucus; and cryopreservation of embryos and semen using computerized freezers. Most of the investigations reviewed in this edition are based more on holistic research than on research at the submicroscopic or molecular level. However, the excitement generated by recent advances in molecular biology and development tend to downgrade the value of whole-animal research. No attempt was made to provide a detailed bibliography, but a selected number of classic papers and review articles are listed at the end of each chapter.
This edition could not have been revised without the cooperation of the contributing authors and their willingness to follow the editorial guidelines. The chapters have been concisely edited, and the major concepts have been summarized in tables supplemented by line drawings and scanning electron micrographs. All chapters have been completely revised and condensed. There have been numerous deletions from the sixth edition, as well as integration of new and modern concepts such as “growth factors,” molecular biology, genetics, and in vitro micromanipulation of gametes and embryos.
Some tabulated appendices include: chromosome numbers and reproductive ability of bovine, caprinae, and equine species and some of their hybrids; preparation of physiologic solutions, sperm stains, tissue culture media, and cryoprotectants. These appendices proved to be helpful for staging demonstrations, laboratory exercises, and training workshops for teachers, laboratory technicians, and students. It is hoped that the seventh edition will be of some help to undergraduate students in animal sciences and veterinary medicine.
B. Hafez/E.S.E. Hafez
Kiawah Island, South Carolina USA
March, 2000
ACKNOWLEDGMENTS
Included in the seventh edition, the contributions and the valuable information were provided by: S.E. Abdelgadir, L.L. Anderson, A.E. Archibong, R.L. Ax, M. Dally, B.A. Didion, D.P. Froman, D.L. Garner, R.D. Geisett, P.J. Hansen, J.D. Kirby, S.S. Koide, R.W. Lenz, C.C. Love, J.R. Malayer, J.A. Proudman, J. Sumar, D.D. Varner, H. Wahid, and Professor M.R. Jainudeen, my friend and long-time associate, who has contributed greatly to the improvement of the table of contents and detailed structure of several chapters. Sincere thanks are due to Ms. Donna Balado and Crystal Taylor of Lippincott Williams & Wilkins for their meticulous and painstaking efforts during the preparation of the book. Special thanks are also due to Vice President Timothy Satterfield for his excellent cooperation and continued interest in the development of animal and veterinary sciences.
CONTRIBUTORS
S.E. Abdelgadir
Asst. Professor of Reproduction Endocrinology/Infertility
Director of Andrology/Embryology
Department of OB/GYN
University of Nevada School of Medicine
Las Vegas, Nevada 89102 USA
L.L. Anderson
Department of Animal Science
Iowa State University
11 Kildee Hall
Ames, Iowa 50011 USA
A.E. Archibong
Director of Andrology/Research
Department of OB/GYN and
Asst. Professor
Department of Anatomy/Physiology
Meharry Medical College
Nashville, Tennessee 37208 USA
615-327-6284 (Tel) 615-327-6296 (Fax)
R.L. Ax, Ph.D.
Professor and Head Department of Animal Science
Adjunct Professor
Department of OB/GYN
University of Arizona
Tucson, Arizona 85721-00038 USA
520-621-7623 (Tel) 520-621-9435 (Fax)
M.R. Dally, Ph.D.
Professor of Animal Science
Hopland Research and Extension Center
University of California
Hopland, California 95449 USA
B. A. Didion, Ph.D.
Dekalb Swine Breeders, Inc.
3100 Sycamore Road
Dekalb, Illinois 60115 USA
D.P. Froman
Department of Animal Sciences
Oregon State University
112 Withycombe Hall
Corvallis, Oregon 97331-6702 USA
541-737-5060 (Tel) 541-737-4174 (Fax)
D.L. Garner
Department of Animal Science
School of Veterinary Medicine
University of Nevada
Mail Stop 202, Reno, Nevada 89557-0104 USA
702-784-6135 (Tel) 702-784-1375 (Fax)
R.D. Geisert
Division of Agricultural Sciences and Natural Resources
Department of Animal Sciences
114 Animal Science
Oklahoma State University
Stillwater, Oklahoma 74078-6051 USA
405-744-6077 (Tel) 405-744-7390 (Fax)
B. Hafez
Reproductive Health Center
78 Surfsong Road
Kiawah Island, South Carolina 29455 USA
843-768-5556 (Tel) 843-768-6494 (Fax)
E.S.E. Hafez
Reproductive Health Center
IVF Andrology Laboratory
78 Surfsong Road
Kiawah Island, South Carolina 29455 USA
843-768-5556 (Tel) 843-768-6494 (Fax)
Ivfreprod@aol.com (e-mail)
P.J. Hansen
Department of Dairy/Poultry Sciences
Institute of Food and Agricultural Sciences
University of Florida
Bldg. 499, Shealy Drive
PO Box 110920
Gainesville, Florida 32611-0920 USA
352-393-5590 (Tel) 352-392-5595 (Fax)
M.R. Jainudeen
University Business Centre
University Administration Building
43400 UPM
Serdang, Selangor, Malaysia
603-948-5649 (Tel/Fax)
(Home Address)
60 Jalan SS 19/5B
47500 Subang Jaya, Selangor, Malaysia
603-734-5694 (Tel/Fax)
jain@pop.jaring (e-mail)
R. Juneja
8402 Timberline Court
Monmouth Junction, New Jersey 08852 USA
732-422-8895 (Tel) 732-940-5711 (Fax)
ARJuneja@aol.com (e-mail)
J.D. Kirby
Dept. of Animal Sciences
Oregon State University
112 Withycombe Hall
Corvallis, Oregon 97331-6702 USA
541-737-5060 (Tel)541-737-4174 (Fax)
S.S. Koide
Population Council
1230 York Avenue
New York, New York 10021 USA
212-327-8731 (Tel) 212-327-7678 (Fax)
R.W. Lenz, Ph.D.
Sire Power, Inc.
R.R.2
Tunkhannock, Pennsylvania 18657 USA
C.C. Love, D.V.M., Ph.D.
Diplomate
American College of Theriogenology
Department of Large Animal Medicine & Surgery
College of Veterinary Medicine
Texas A&M University
College Station, Texas 77843-4475 USA
J.R. Malayer
Division of Agricultural Sciences and Natural Resources
Department of Animal Science
114 Animal Science
Oklahoma State University
Stillwater, Oklahoma 74078-6051 USA
405-744-6077 (Tel) 405-744-7390 (Fax)
C.A. Pinkert
The University of Alabama at Birmingham
Department of Comparative Medicine
227 Volker Hall
1670 University Boulevard
Birmingham, Alabama 35294-0019 USA
205-934-9574 (Tel) 205-975-4390 (Fax)
Pinkert@uab.edu (e-mail)
J.A. Proudman
Research Physiologist
Germplasm and Gamete Physiology Laboratory
Livestock and Poultry Sciences Institute
BARC-East
Building 262
Beltsville, Maryland 20705 USA
301-504-8094 (Tel) 301-504-8546 (Fax)
JohnP@lpsi.barc.usda.gov (e-mail)
J.B. Sumar
Avenida De Los Incas 1412
Wanchaq, Cusco, Peru
51 (84) 224 614 (Tel) 51 (84) 221 632 (Fax)
D.D. Varner, D.V.M., M.S.
Diplomate
American college of Theriogenology
Department of Large Animal Medicine & Surgery
College of Veterinary Medicine
Texas A&M University
College Station, Texas 77843-4475 USA
H. Wahid
Department of Veterinary Science
Clinical Studies
University Putra
Malaysia, 43400
Serdang, Selangor, Malaysia
603-948-6101 X1829 (Tel) 603-948-6317 (Fax)
wahid@vet.upm.edu.my (e-mail)
The male gonads, the testes, lie outside the abdomen within the scrotum, which is a purselike structure derived from the skin and fascia of the abdominal wall. Each testis lies within the vaginal process, a separate extension of the peritoneum, which passes through the abdominal wall at the inguinal canal. The deep and superficial inguinal rings are the deep and superficial openings of the inguinal canal. Blood vessels and nerves reach the testis in the spermatic cord, which lies within the vaginal process; the ductus deferens accompanies the vessels but leaves them at the orifice of the vaginal process to join the urethra. Besides permitting the passage of the vaginal process and its contents, the inguinal canal also gives passage to vessels and nerves supplying the external genitalia.
The spermatozoa leave the testis by efferent ductules that lead into the coiled duct of the epididymis, which continues as the straight ductus deferens. Accessory glands discharge their contents into the ductus deferens or into the pelvic portion of the urethra.
The urethra originates at the neck of the bladder. Throughout its length it is surrounded by cavernous vascular tissue. Its pelvic portion, which is enclosed by striated urethral muscle and receives secretions from various glands, leads into a second penile portion at the pelvic outlet. Here it is joined by two more cavernous bodies to make up the body of the penis, which lies beneath the skin of the body wall. A number of muscles grouped around the pelvic outlet contribute to the root of the penis. The apex or free part of the penis is covered by modified skin—the penile integument; in the resting condition it is enclosed within the prepuce. The topographic features of the organs of the important farm species are shown in Figure 1-1.
The testis and epididymis are supplied with blood from the testicular artery, which originates from the dorsal aorta near the embryonic site of the testes. The internal pudendal artery supplies the pelvic genitalia and its branches leave the pelvis at the ischial arch to supply the penis. The external pudendal artery leaves the abdominal cavity via the inguinal canal to supply the penis, scrotum, and prepuce. Lymph from the testis and epididymis passes to the lumbar aortic lymph nodes. Lymph from the accessory glands, urethra, and penis passes to the sacral and medial iliac nodes. Lymph from the scrotum, prepuce, and peripenile tissues drains to the superficial inguinal lymph nodes.
Afferent and efferent (sympathetic) nerves accompany the testicular artery to the testis. The pelvic plexus supplies autonomic (sympathetic and parasympathetic) fibers to the pelvic genitalia and to the smooth muscles of the penis. Sacral nerves supply motor fibers to the striated muscles of the penis and sensory fibers to the free part of the penis. Afferent fibers from the scrotum and prepuce travel mainly in the genitofemoral nerve.
The testes develop in the abdomen, medial to the embryonic kidney (mesonephros). The plexus of ducts within the testis becomes connected to mesonephric tubules and so to the mesonephric duct, to form the epididymis, ductus deferens, and vesicular gland. The prostate and bulbourethral glands form from the embryonic urogenital sinus and the penis forms by tubulation and elongation of a tubercle that develops at the orifice of the urogenital sinus.
Two agents produced by the fetal testis are responsible for this differentiation and development (1). Fetal androgen causes development of the male reproductive tract. “Müllerian inhibiting substance,” a glycoprotein, is responsible for suppression of the paramesonephric (Müllerian) ducts from which the uterus and vagina develop (2). Abnormalities in differentiation and development of gonads and ducts can result in varying degrees of intersexuality (3).
FIGURE 1-1. Diagram of the male reproductive tracts as seen in left lateral dissections. a, Ampulla; bu, bulbourethral gland; cap. e, caput epididymidis, caud. e, cauda epididymidis; cp, left crus of penis, severed from the left ischium; dd, ductus deferens; ds, dorsal diverticulum of prepuce; es, prepenile prepuce; fe, free part of the penis; is, preputial fold; pg, prostate gland; r, rectum; rp, retractor penls muscle; s, scrotum; sf, sigmoid flexure; t, testis; up, urethral process; vg, vesicular gland. (Adapted from Popesko, Atlas der topographischen anatomie der Haustiere. Vol. 3, Jena: Fischer, 1968.)
During testicular descent (4), the gonad migrates caudally within the abdomen to the deep inguinal ring. It then traverses the abdominal wall to emerge at the superficial inguinal ring, which is, in fact, the much-enlarged foramen of the genitofemoral nerve (L3, L4). The testis completes its migration by passing fully into the scrotum. Descent is preceded by the formation of the vaginal process, a peritoneal sac extending through the abdominal wall and enclosing the inguinal ligament of the testis. The inguinal ligament of the gonad is often called the gubernaculum testis, and it terminates in the region of the scrotal rudiments. Descent follows the line of the gubernaculum testis. The time of descent varies (Table 1-1). In the horse, the epididymis commonly enters the inguinal canal before the testis, and that part of the inguinal ligament connecting testis and epididymis (proper ligament of testis) remains extensive until after birth.
TABLE 1-1. Development of the Male Reproductive Trace in Farm Animals (weeks)
Sometimes the testis fails to enter the scrotum. In this condition (cryptorchidism), the special thermal needs of testis and epididymis are not met, although the endocrine function of the testis is unimpaired. Bilaterally cryptorchid males therefore show more or less normal sexual desire but are sterile. Occasionally some of the abdominal viscera pass through the orifice of the vaginal process and enter the scrotum; scrotal hernia is particularly common in pigs.
Each component of the reproductive tracts of all farm animals grows in size relative to overall body size and undergoes histologic differentiation. Functional competence is not achieved simultaneously in all components of the reproductive system. Thus, in the bull, the capacity for erection of the penis precedes the appearance of sperm in the ejaculate by several months. In rams, the terminal segment of the epididymis is morphologically “adult” at 6 weeks, but the initial segment is not so until 18 weeks (5). At puberty all the components of the male reproductive system have reached a sufficiently advanced stage of development for the system as a whole to be functional. The period of rapid development that precedes puberty is known as the prepubertal period, although this period is itself sometimes referred to as “puberty,” During the postpubertal period, development continues and the reproductive tract reaches full sexual maturity months or even years after the age of puberty. In horses, significant increases in testicular weight, daily sperm production, and epididymal sperm reserves occur at 15 years of age. Some important anatomic changes that occur during postnatal development are summarized in Table 1-1.
The testis is secured to the wall of the vaginal process along the line of its epididymal attachment. The position in the scrotum and the orientation of the long axis of the testis differ with the species (Fig. 1-1). The arrangement of tubules and ducts within the testis in the bull is shown in Figure 1-2. The histologic and cytologic characteristics of the cellular components of the seminiferous tubules are summarized in Table 1-2. The rete testis is lined by a nonsecretory cuboidal epithelium.
Testicular size varies throughout the year in seasonal breeders (ram, stallion, camel). Removal of one testis results in considerable enlargement of the remaining gonad (up to 80% increase in weight), In the unilateral cryptorchid, removal of the descended testis may be followed by descent of the abdominal testis as it enlarges.
The interstitial (Leydig) cells, which lie between the seminiferous tubules, secrete male hormones into the testicular veins and lymphatic vessels. The spermatogenic cells of the tubule divide and differentiate to form spermatozoa. Just before puberty, the sustentacular (Sertoli) cells of the tubule form a barrier (6), which isolates the differentiating germ cells from the general circulation. These sustentacular cells contribute to fluid production by the tubule and may produce the Müllerian-inhibiting factor found in the rete fluid of adult males (2). The sustentacular cells do not increase in numbers after puberty is attained. This may limit spermiogenesis. Sperm production increases with age in the postpubertal period and is subject to seasonal changes in many species. Castration of prepubertal males suppresses sexual development. Regressive changes in behavior and structure take place following castration of adult males. Castration is a standard procedure in animal husbandry to modify aggressive male behavior and to eliminate undesirable carcass qualities, e.g., boar taint.
FIGURE 1-2. Schematic drawing of the tubular system of the testis and epididymis in the bull (for clarity the duct system of the rete testis is omitted). cap. e, Caput epididymidis; caud. e, cauda epididymidis; corp. e, corpus epididymidis; dd, ductus deferens; de, duct of the epididymis; ed., efferent ductule; lb, lobule with seminiferous tubules; rt, rete testis; st, straight tubule; t, testis. (Simplified from Blom and Christensen. Nord Vet Med 1968;12:453.)
Spermatogenesis disorders are monitored by changes in sperm parameters in the ejaculate or by infertility. Turner et al, (7) conducted extensive studies to identify the proteins which play major roles in spermatogenesis and are subsequently transported into the blood stream.
Autonomic innervation of the testis plays a major role in regulating the functions of the male genitourinary tract. Adrenergic, cholinergic, and nonadrenergic noncholinergic (NANC) mechanisms operate in a highly orchestrated fashion to ensure reliable storage and release of urine from the bladder to regulate the transport and storage of sperm in the reproductive tract and coordinate the emission/ejaculation of the sex accessory glands (8).
TABLE 1-2. Functional Histology of the Mammalian Testis
| SEGMENT | HISTOLOGIC CHARACTERISTICS |
| Tunica albuginea | A thick, white capsule of connective tissue surrounding the testis; made primarily of interlacing series of collagenous fiber. |
| Seminiferous tubules | Appear as large isolated structures, round or oblong in outline; varying appearance due to the complex coiling of the tubules at many different angles and levels. Between the tubules are masses of interstitial (Leydig) cells, which produce the male sex hormones. |
| Spermatogonia | Lie in the outermost region of the tubule; round nuclei appear as an irregular layer within surrounding connective tissue. Nuclei are small size and dark stain due to presence of large numbers of chromatin granules. |
| Primary spermatocytes | Located just inside an irregular layer of spermatogonia and Sertoli cells; nuclei are larger than those of the spermatogonia and stain lighter. |
| Secondary spermatocytes | Maturation divisions and secondary spermatocytes are not seen in the average tubule owing to the short duration of these stages. |
| Spermatids | Located internally to primary spermatocytes. Layer of spermatids may be several cells in thickness. Sperm lie along the border of the lumen. The sperm heads are lodged in deep indentations of the surface of the Sertoli cell. |
| Sertoli cells | Large and relatively clear except for the prominent, dark-staining nucleolus. Cytoplasm is diffuse, and its limits are indefinite. |
The adrenergic innervation may play a role in mediating epididymal function. The sympathetic innervation within the epididymis is necessary for neuromuscular events required for the transport of sperm. The neuronal input may play an important role in the maintenance of epididymal function (8).
For effective functioning, the mammalian testes must be maintained at a temperature lower than that of the body. Anatomic features of the testis and scrotum permit the regulation of testicular temperature. Temperature receptors in the scrotal skin can elicit responses that tend to lower whole body temperature and provoke panting and sweating (9). The scrotal skin is richly endowed with large adrenergic sweat glands, and its muscular (dartos) component enables it to alter the thickness and surface area of the scrotum and vary the closeness of the contact of the testes with the body wall. In the horse, this action may be supported by the smooth muscle within the spermatic cord and tunica albuginea, which can lower or raise the testis. In cold conditions, these smooth muscles contract, elevating the testes and wrinkling and thickening the scrotal wall. In hot conditions the muscles relax, lowering the testes within the thin-walled pendulous scrotum. The advantages offered by these mechanisms are enhanced by the special relationship of the veins and arteries.
In all farm animals, the testicular artery is a convoluted structure in the form of a cone, the base of which rests on the cranial or dorsal pole of the testis. These arterial coils are intimately enmeshed by the so-called pampiniform plexus of testicular veins (10). In this countercurrent mechanism, arterial blood entering the testis is cooled by the venous blood leaving the testis. In the ram, blood in the testicular artery falls 4 °C in its course from the superficial inguinal ring to the surface of the testis; the blood in the veins is warmed to a similar degree between the testis and the superficial ring. The position of the arteries and veins close to the surface of the testis tends to increase direct loss of heat from the testis. In the boar, the scrotum is less pendulous (Fig. 1-1) and sweating is less efficient. This may explain the smaller difference between scrotal and rectal temperatures (3.2 °C) (11).
Three anatomic parts of the epididymis are recognized (Fig. 1-2). The caput epididymidis (head), in which a variable number of efferent ductules (13 to 20) (12) join the duct of the epididymis. It forms a flattened structure applied to one pole of the testis. The narrow corpus epididymidis (body) terminates at the opposite pole in the expanded cauda epididymidis (tail). The middle region of each efferent duct shows marked secretory activity (13). The convoluted duct of the epididymis is very long (bull, 36 m; boar, 54 m). The wall of the duct of the epididymis has a prominent layer of circular muscle fibers and a pseudostratified epithelium of columnar cells. Three segments of the duct of the epididymis can be distinguished histologically; these do not coincide with the gross anatomic regions (14).
There is a progressive decrease in the height of the epithelium and stereocilia and a widening of the lumen throughout the three segments. The first two segments are concerned with sperm maturation, whereas the terminal segment is for sperm storage.
The lumen of the epididymal tubules is lined with epithelium made of a basal layer of small cells and a surface layer of tall columnar ciliated cells.
The mucosa of the ductus deferens is thrown into longitudinal folds. Near the epididymal end, the epithelium resembles that of the epididymis: the nonciliated cells have little secretory activity. The lumen is lined with pseudostratified epithelium. The ampulla of the ductus deferens is furnished with branched tubular glands, which, in the stallion, are highly developed and contribute ergothioneine to the ejaculate. The ejaculatory duct enters the urethra. Fluid uptake and spermiophagy take place in the epithelium of the ejaculatory duct (15). Scanning electron microscopy has been used to evaluate functional ultrastructure of male reproductive organs with emphasis on spermatogenesis (Fig. 1-3). Large volumes of fluid (up to 60 ml in the ram) leave the testis daily, and most of this is absorbed in the caput epididymidis by the initial segment of the duct of the epididymis. Transport of sperm through the epididymis takes about 9 to 13 days. Maturation of sperm occurs during transmit through the epididymis; motility increases as sperm enter the corpus epididymidis. The environment of the sperm in the cauda epididymidis provides factors that enhance fertilizing ability. Sperm from this region give higher fertility than those from the corpus epididymidis (14).
Spermatozoa stored in the epididymis retain fertilizing capacity for several weeks; the cauda epididymidis is the principal storage organ, and it contains about 75% of the total epididymal spermatozoa. The special ability of the cauda epididymidis to store sperm depends on low scrotal temperatures and on the action of male sex hormone (16). Sperm stored in the ampullae constitute only a small part of the total extra-gonadal sperm reserves. Small numbers of nonmotile sperm appear in ejaculates collected weeks or even months after castration.
FIGURE 1-3. Scanning electron micrographs (SEM) (A) Luminal surface of an efferent duct with ciliated and nonciliated cells and a sperm. (B) Short microvilli on the luminal surface of nonciliated cells in the efferent ducts. The spermatozoa1 cytoplasmic droplet (CD), acrosome (A), and middle piece (MP) are distinguishable (×6,500). (C) Cross section of a seminiferous tubule (ST). Note several “stages” of spermatogenesis, encased in a muscular boundry tissue. (A and B from Connell CJ. Spermatogenesis. In: Hafez ESE, ed. Scanning Electron Microscopy of Human Reproduction. Ann Arbor, MI: Ann Arbor Science Pubs, 1978. C courtesy of Dr. Larry Johnson, from Johnson L, et al. Am J Vet Res 1978.)
The prostate and bulbourethral glands pour their secretions into the urethra, where at the time of ejaculation, they are mixed with the fluid suspension of sperm and ampullary secretions from the ductus deferens. Weber et al (17) have demonstrated volumetric changes in the accessory glands of the stallion resulting from sexual stimulation (increased volume) and ejaculation (reduced volume).
THE SEMINAL VESICLES. These lie laterally to the terminal parts of each ductus deferens. In ruminants, they are compact lobulated glands. In the boar, they are large and less compact. In the stallion, they are large pyriform glandular sacs. The duct of the seminal vesicles and the ductus deferens may share a common ejaculatory duct that opens into the urethra.
THE PROSTATE GLAND. A distinct lobulated external part of body lies outside the thick urethral muscle, and a second internal or disseminated part surrounds the pelvic urethra. The disseminate prostate extends caudally as far as the ducts of the bulbourethral glands. The body of the prostate is small in the bull and large in the boar. In the stallion, the prostate gland is wholly external.
THE BULBOURETHRAL GLANDS. These are dorsal to the urethra near the termination of its pelvic portion. In the bull they are almost hidden by the bulbospongiosus muscle. They are large in the boar and contribute the gel-like component of boar semen. In ruminants and the boar, the ducts of the bulbourethral glands open into urethral recesses (18).
THE URETHRAL GLANDS. The bull lacks urethral glands comparable with those found in man (19). Glands of this name in the horse have been considered comparable to the disseminate prostate of ruminants.
Apart from providing liquid vehicle for the transport of sperm, the function of the accessory glands is obscure although much is known about the specific chemical agents contributed by the glands to the ejaculate (20, 21). Fructose and citric acid are important components of seminal vesicle secretions of domestic ruminants. Citric acid alone is found in stallion seminal vesicle; boar seminal vesicle also contain little fructose and are characterized by a high content of ergothioneine and inositol.
Spermatozoa from the cauda epididymidis are capable of fertilization when inseminated without the addition of accessory gland secretions. The gel-like fraction of the boar ejaculate forms a plug in the vagina of mated females. In commercial insemination practice, this fraction is removed from the semen by filtration.
FIGURE 1-4. The pelvic genitalia, within the pelvic bones, as seen from a dorsal view. a, ampulla; bs, bulbospongiosus muscle; bu, bulbourethral gland; dd, ductus deferens; ic, ischiocavernosus muscle; pb, body of prostate gland; pel. u, pelvic urethra; rp, retractor penis muscle; ub, urinary bladder; vg, vesicular gland. (Diagrams of bull, boar and stallion redrawn from Nickel R. Tierarztl Umschau 1954;9:386.)
In large animals, rectal palpation of some of the accessory glands is possible. The positions of these glands relative to the bony pelvis are shown in Figure 1-4.
In the pig, the size of the bulbourethral glands can be used to differentiate the cryptorchid from the castrated state. After prepubertal castration, the bulbourethral glands are small. In boars with retained testes, the glands are of normal size (22). These differences can easily be felt, ventral to the rectum, with a finger inserted through the anus.
In the mammalian penis, three cavernous bodies are aggregated around the penile urethra. The corpus spongiosum penis—which surrounds the urethra—is enlarged. This bulb is covered by the striated bulbospongiosus muscle. The corpus cavernosum penis arises as a pair of crura from the ischial arch, which are covered by ischiocavernosus muscles. A thick covering (tunica albuginea) encloses the cavernous bodies. The retractor penis muscles in ruminants and swine control the effective length of the penis by their action on the sigmoid flexure.
In the stallion, the cavernous bodies contain large cavernous spaces; during erection, considerable increases in size result from accumulation of blood in these spaces. In bull, ram, and boar the cavernous spaces of the corpus cavernosum penis is small, except in the crura and at the distal bend of the sigmoid flexure.
In ruminants and swine, the orifice of the prepuce is controlled by the cranial muscle of the prepuce; a caudal muscle may also be present. In the boar there is a large dorsal diverticulum in which urine and epithelial debris accumulate.
Sexual stimulation produces dilatation of the arteries supplying the cavernous bodies of the penis (especially the crura). Stiffening and straightening of the penis in ruminants is caused by the ischiocavernosus muscle, which pumps blood from the cavernous spaces of the crura into the rest of the corpus cavernosum penis.
Erection failures (impotence) arise from structural defects rather than from psychological causes (23). Rising pressure in the corpus cavernosum penis produces considerable elongation of the ruminant and porcine penis with little dilation (24). When the penis of the bull is protruded, the prepuce is everted and stretched over the protruded organ.
FIGURE 1-5. Diagrams to show the shape of the free end of the penis. (A1) The shape of the penis just before intromission. (A2) The shape after intromission when spiral deviation has occurred. (B) The shape of the penis during natural service. (C) Does not show the full degree of spiralling that occurs during service. (D) Drawn after injection and shows enlargement of the erectile bodies. (A1, A2, and B from photographs. C and D from fixed specimens. Not drawn to scale.)
In normal service, this occurs after intromission. If it occurs before the penis enters the vestibule, intromission cannot be achieved.
Intromission in the bull lasts for about 2 seconds, and straightening of the penis after withdrawal often occurs abruptly as the dorsal apical ligament reasserts its action in keeping the penis straight. Withdrawal into the prepuce follows as the pressure in the cavernous spaces subsides. The fibrous architecture of the corpus cavernosum penis in the region of the sigmoid flexure tends to reform the flexure; this is assisted by shortening of the retractor penis muscle. The terminal 5 cm or so of the boar penis are spiraled (Fig. 1-5), and during erection the whole visible length of the free end of the penis becomes spiraled (24). Intromission lasts for up to 7 minutes, during which time a large volume of semen is ejaculated. Spiral deviation does not occur in the ram or goat, and intromission is of short duration. In the horse intromission lasts for several minutes.
Emission consists of movement of the spermatic fluid along the ductus deferens to the pelvic urethra, where it is mixed with secretions from the accessory glands. Ejaculation is the passage of the resultant semen along the penile urethra. Emission is brought about by smooth muscles, under the control of the autonomic nervous system. Electrical stimulation of ejaculation in farm animals is a crude imitation of the complex natural mechanisms. During natural service, the sensory nerve endings in the penile integument and the deeper penile tissues are essential to the process of ejaculation.
TABLE 1-3. Age and Weight of First Breeding and Semen Characteristics
Passage of semen along the ductus deferens is continual during sexual inactivity. Prinz and Zaneveld (25) suggest that during sexual rest a complex random or cyclic process of sperm removal from the cauda epididymidis may aid the regulation of sperm reserves. Sexual excitement and ejaculation are accompanied by contractions of the cauda epididymidis and ductus deferens, which increase the rate of flow. Overall, the number of sperm passing through the ductus deferens is not increased by sexual activity.
Muscular contraction of the wall of the duct is controlled by sympathetic autonomic nerves of the pelvic plexus derived from the hypogastric nerves. In normal stallions, α-receptor stimulation and β-receptor blockade increase the sperm concentration in the ejaculate (26).
During ejaculation the bulbospongiosus muscle compresses the penile bulb and so pumps blood from the penile bulb into the remainder of the corpus spongiosum penis. Unlike the corpus cavernosum penis, this cavernous body is normally drained by distal veins; peak pressures recorded during ejaculation are much lower than those in the corpus cavernosum penis (27). The waves of pressure passing down the penile urethra may help to transport the ejaculate. Pressure changes in the corpus spongiosum penis during ejaculation are transmitted to the corpus spongiosum glandis; the glans penis enlarges in the ram, goat, and stallion but not in the bull.
Species differences in the male reproductive organs are shown in Figure 1-1. These organs can move from a wholly scrotal to a wholly abdominal position. Differences in relative size of the accessory glands are reflected in the semen characteristics (Table 1-3).
1. Gondos B. Development and differentiation of the testis and male reproductive tract. In: Steinberger A, Steinberger E, eds. Testicular Development: Structure and Function. New York: Raven Press, 1980.
2. Vigier B, Tran D, duMesuil du Brusson F, Heyman Y, Josso N. Use of monoclonal antibody techniques to study the ontogeny of bovine anti-Müllerian hormone. J Reprod Fertil 1983;69:207.
3. Hare WCD, Singh E. Cytogenetics in animal reproduction. Farnham: Royal Commonwealth Agricultural Bureau, 1979.
4. Wensing CJG. Testicular descent in the rat and a comparison of this process in the rat with that in the pig. Anat Rec 1986;214:154.
5. Nilnophakoon N. Histological studies on the regional postnatal differentiation of the epididymis in the ram. Anat Histol Embryol 1978;7:253.
6. Vazama F, Nishida T, Kurohmara M, Hayashi Y. The fine structure of the blood-testis barrier in the boar. Jap J Vet Sci 1988;50:1259.
7. Turner KJ, McKinnell C, McLaren TT, Qureshi SJ, Saunders TK, Foster MD, Sharpe RM. Detection of germ cell-derived proteins in potential for monitoring spermatogenesis in vivo. J Androl 1996;17:127–136.
8. Ricker D, Chamness SL, Hinton BT, Chang TK. Changes in luminal fluid protein composition in the rat cauda epididymidis following partial sympathetic denervation. 1996;17:117–126.
9. Robertshaw D, Vercoe JE. Scrotal thermoregulation of the bull. (Bos sp). Aust J Agric Res 1980;31:401.
10. Hees H, Kohler T, Leiser R, Hees I, Lips T. Gefäss-Morphologie des Rinderhodens Licht-und rasterelektron-mikroskopische Studien. Anat Anz 1990;170:119.
11. Stone BA. Thermal characteristics of the testis and epididymis of the boar. J Reprod Fertil 1981;63:551.
12. Hemeida NA, Sack WO, McEntee K. Ductuli efferentes in the epididymis of boar, goat, ram, bull and stallion. Am J Vet Res 1978;39:1892.
13. Goyal HO, Eljack A, Mobini C. Regional differences in the morphology of the ductuli efferentes of the goat. Anat Histol Embryol 1988;17:369.
14. Amann RP. Function of the epididymis in bulls and rams. J Reprod Fertil Suppl 1987;34:115.
15. Abou-Elmagd A, Wrobel KH. The epithelial lining of the bovine ejaculatory, duct. Acta Anat 1990;139:60.
16. Foldesey RG, Bedford JM. Biology of the scrotum (1): Temperature and androgen as determinants of the sperm storage capacity of the rat cauda epididymidis. Biol Reprod 1982;26:673.
17. Weber JA, Geary RT, Woods GL. Changes in accessory sex glands of stallions after sexual preparation and ejaculation. J Am Vet Med Assoc 1990;196:1084.
18. Garrett PD. Urethral recess in male goats, sheep, cattle and swine. J Am Vet Med Assoc 1987;191:689.
19. Kainer RA, Faulkner LC, Abdel-Raouf M. Glands associated with the urethra of the bull. Am J Vet Res 1969;30:963.
20. Spring-Mills E, Hafez ESE, eds. Accessory glands of the male reproductive tract. Ann Arbor: Ann Arbor Science Pubs, 1979.
21. Spring-Mills E, Hafez ESE, eds. Male accessory organs. New York: Elsevier, 1980.
22. Lauwers J, Nicaise M, Simoens O, de Vos NR. Morphology of the vesicular and bulbourethral glands in barrows and the changes induced by diethyl stilboestrol. Anat Histol Embryol 1984;13:50.
23. Glossop CE, Ashdown RR. Cavernosography and differential diagnosis of impotence in the bull. Vet Rec 1986;118:357.
24. Ashdown RR, Barnett SW, Ardalani G. Impotence in the boar. (1): Angioarchitecture and venous drainage of the penis in normal boars. Vet Rec 1981;109:375.
25. Prinz GS, Zaneveld LJD. Radiographic study of fluid transport in the rabbit vas deferens during sexual rest and after sexual activity. J Reprod Fertil 1980;58:311.
26. Klug E, Deegen E, Lazarz B, Rojem I, Merkt M. Effect of adrenergic neurotransmitters upon the ejaculatory process in the stallion. J Reprod Fertil Suppl 1982;32:31.
27. Beckett SD. Circulation to male reproductive organs. In: Shepherd ST, Aboud FM, eds. Handbook of Physiology—The Cardiovascular System III. Washington, D.C., American Physiological Society, 1983.
Ardalani G, Ashdown RR. Venous drainage of the bovine corpus covernosum penis in relationship to penile dimensions and age. Res Vet Sci 1988;45:174.
Ashdown RR, Barnett SW, Ardalani G. Impotence in the bull. (2): Occlusion of the longitudinal canals of the corpus covernosum penis. Vet Rec 1979;104:598.
Ashdown RR, Smith JA. The anatomy of the corpus covernosum penis of the bull and its relationship to spiral deviation of the penis. J Anat 1969;104:153.