Equine Breeding Management and Artificial Insemination

Juan C. Samper

• Publisher: Saunders
• Year: 2008
• ISBN:
  9781437711226
• Edition: 2
• Topic: Medicina
• Subtopic: Scienza veterinaria equina

Put the principles of good breeding management into practice with Equine Breeding Management and Artificial Insemination, 2nd Edition for reproductive success! Practical information on the reproductive management of both thoroughbred and warmblood breeding operations prepares you to effectively breed even problem mares and stallions. Plus, detailed content on techniques, procedures, reproductive physiology, and more help you increase reproductive efficiency as well as track and improve your results throughout each breeding season.

• A section on reproduction efficiency evaluation includes a worksheet to evaluate the performance of both mares and stallions during each breeding season, and helps you compare reproductive performance with previous breeding seasons.
• Detailed descriptions of procedures and techniques including embryo transfer, artificial insemination, and more enable you to implement the methods for better breeding results.
• Practical information on reproductive management of both thoroughbred and warmblood breeding operations enhance the fertility of problem mares and stallions.
• World-renowned authors and contributors with years of practical knowledge and experience provide cutting-edge information.

• Vibrant full-color design and photographs show accurate representations of clinical appearance.
• Chapters covering the latest reproductive techniques improve chances of successful breeding, and improve survival rates after the birth of the foal.
• Vital chapters with information on recognizing potential problems help you quickly identify warning signs before fertility is negatively affected.

Chapter 1 ANATOMY AND PHYSICAL EXAMINATION OF THE STALLION

Tracey S. Chenier

This chapter discusses the normal anatomy of both external and internal genitalia of the stallion, including the scrotum, testes, epididymides, spermatic cords, penis, prepuce, ampullae, vesicular glands, prostate gland, and bulbourethral (BU) glands. A brief overview of the relevant findings of physical examination and ultrasonographic examination is included in each section.

MANAGEMENT OF BREEDING STALLIONS

Equine practitioners involved with the care of breeding stallions should consider the importance of frequent and routine examinations of those stallions. A thorough understanding of the physical anatomy of the stallion places the clinician in a better position to monitor the health and reproductive status of the stallions under his or her care. Familiarity with the appearance and palpation findings of normal structures is imperative for detecting what can be subtle deviations from normal. As part of routine management, all normal breeding stallions should receive a complete breeding soundness examination at least twice yearly. An initial examination should occur in advance of the breeding season to allow time to address any potential problems. Stallions with ongoing problems should be examined monthly to monitor progression of disease conditions. This examination should include a thorough physical examination; palpation and ultrasound of the scrotum, testes, and spermatic cords; careful inspection of the erect penis and sheath; and rectal examination with ultrasound of the accessory glands. Additional tests such as routine blood panels for complete blood count, profile, and hormonal tests might be considered in individual cases. Every ejaculate should be examined for color, semen volume, total number of sperm, motility. and morphology. Total number of sperm and morphology are especially important as indicators of testicular health. Early detection of problems can allow management changes to prolong the fertility of stallions with many conditions.

EXTERNAL GENITALIA

The Scrotum

The scrotum of the stallion is located high in the inguinal region and is slightly pendulous. It forms two distinct pouches that contain, protect, and thermoregulate the testes, epididymides, spermatic cords, and cremaster muscles. The testes are located in the scrotum to maintain testicular temperature at several degrees below core body temperature, a necessity for normal spermatogenesis.^1,2 Thermography of scrotal contents of stallions has demonstrated a scrotal skin temperature of 33°C, with testis contents at 30.5° to 32.5°C.¹

The wall of the scrotum consists of four layers: (1) skin, (2) tunica dartos, (3) scrotal fascia, and (4) parietal vaginal tunic.^3-6 The scrotal skin is thin, generally hairless, and slightly oily, containing numerous sebaceous and sweat glands, which assist in testis thermoregulation.^3,7 The tunica dartos layer is adherent to the scrotal skin and consists of muscular and fibroelastic tissue. It lines both scrotal pouches and extends into the median septum, seen externally as the median raphae of the scrotum. The degree of contraction or relaxation of this layer allows alterations in the size, shape, and position of the scrotum in relation to the body wall, thereby aiding testis thermoregulation. The scrotal fascia, a loose connective tissue layer between the tunica dartos and parietal vaginal tunic, allows the testes and associated parietal tunic layer to move freely within the scrotum.⁵ The innermost layer of the scrotum, the parietal vaginal tunic, is an evagination of the parietal peritoneum through the inguinal rings, which forms during testicular descent. This layer forms a sac that lines the scrotum and is closely apposed to the visceral vaginal tunic, the outer layer of the testis. The vaginal cavity is the space between the parietal and visceral layers of the vaginal tunic. It normally contains a very small amount of viscous fluid to allow some free movement of the testis within. The vaginal cavity is a potential space within which considerable fluid may accumulate as a result of a variety of causes.

The scrotum of the normal stallion should appear slightly pendulous, globular, and generally symmetric (Fig. 1-1). Normal variations may be observed in the positioning of the testes if one is relatively anterior to or ventral to the other. The skin should have no evidence of trauma, scarring, or skin lesions. Palpation of the scrotum of a normal stallion reveals a thin and pliable covering, which slides loosely and easily over the testicles and epididymides within.

Figure 1-1 The scrotum of the stallion is slightly pendulous, with the testes held in a horizontal position. Frequently one testicle may be held much higher to the body wall than the other, as shown.

The Testes

Testicular Descent

The testicles normally descend into a scrotal position between the last 30 days of gestation and the first 10 days postpartum (Fig. 1-2).^7,8-11 In some colts, the testes may descend into the inguinal region and remain there for some time before fully descending into the scrotum. The hormonal factors involved in testicular descent in the stallion are poorly understood. Research in the rat has demonstrated the involvement of androgens and luteinizing hormone (LH) in the process. The timing of testicular descent coincides with significant rises in endogenous gonadotropins. It appears that an intact hypothalamic-pituitary axis, adequate LH levels, and several physical factors must be present for normal testicular descent to occur. In midgestation, the abdominal fetal testis hypertrophies significantly, resulting in the developing gonad resting close to the vaginal ring. The developing gubernaculum and abdominal pressure hold the testes in place until late gestation, despite considerable decrease in the size of the gonads later in gestation. The caudal ligament, which attaches the epididymis to the caudal pole of the testis, initially lengthens faster than the rest of the gubernaculum, resulting in the epididymis being drawn into the vaginal ring and inguinal canal. Dilation of the vaginal ring and inguinal canal, combined with abdominal pressure and traction from the gubernaculum, eventually draws the testes into the ring as well.

Figure 1-2 Stages of testicular descent into the scrotum of the horse fetus. A, Fetus at 75 days of gestation. B, Fetus at 175 days of gestation. C, Fetus near term (330 days of gestation).

(From Varner DD, Schumacher J, Blanchard T, et al: Diseases and Management of Breeding Stalli...