Seasonality

Gel Free Volume Sperm

In common with mares and many other mammals, the reproductive activity of the stallion is governed by season. He is, therefore, classified as a seasonal Table 3.3. Change in daily spermatozoan production (DSP) g 1 of testicular tissue with age (Johnson and Thompson, 1983). Table 3.3. Change in daily spermatozoan production (DSP) g 1 of testicular tissue with age (Johnson and Thompson, 1983). breeder. The length of the breeding season depends upon many factors, including breed, environmental...

Commencement of reproductive activity

Puberty heralds the start of reproductive activity in the stallion. The exact timing of puberty is unclear but has been defined as the time at which a stallion can produce 50 X 106 spermatozoa per ejaculate with greater than 10 progressive motility. Using these parameters, puberty is seen to commence at 21 months (Clay and Clay, 1992). The exact timing of puberty is known to be affected by several factors, including breed, management and the rate of stallion growth and development. Classically...

Hypothalamic and pituitary hormones

Numerous hormones have an effect upon or are produced by the hypothalamus or the pituitary. These will be discussed in turn, but it must be remembered that the hormones do not work in isolation rather, they form part of an integrated system of whole body control. As indicated previously, one of the major means of controlling the hypothalamus is via the hormone melatonin, which is produced by the pineal gland. Melatonin is secreted during the hours of darkness and, due to its antigonadotrophic...

Testicular hormones

Testosterone Stallions

The final level in the hypothalamic-pituitary-gonadal axis in the stallion is the testes. Within the testes there are two major cell populations or target organs the Leidig cells and the Sertoli cells. These two cell populations have two major roles steroid hormone production and the production of spermatozoa. A close feedback association must exist between these various functional structures within the testes. The exact nature of their control is unclear in the horse, much evidence being...

The hypothalamicpituitarygonadal axis

Thirst Axis

The hypothalamic-pituitary-testis axis is responsible for the control of reproduction in the stallion. The system works in a cascade fashion, with appropriate negative feedback loops. The axis is also controlled by secretions of the pineal gland. The pineal gland lies above and behind the hypothalamus, held within a fibrous capsule. Septa extend into the gland from separate masses of round epithelial cells. These cells produce the hormone melatonin from tryptophan melatonin has an...

Deposition of spermatozoa

Stallions Penis

There are three stages involved in the deposition of spermatozoa into the genital tract of the mare erection, emission and ejaculation. Each will be considered in turn. Erection is the first reaction observed after sexual stimulation. It is the result of both physical stimulation, via nerve-end stimulation in the highly innervated area of the glans penis, and psychological stimulation from the Fig. 3.5. Transverse cross-sections through the glans penis of the stallion see also Fig. 3.6 . Fig....

Hormonal regulation and control of spermatogenesis

In summary, the hormone regulation of stallion reproduction and spermato-genesis involves a three-tier system the hypothalamic-pituitary-gonadal axis. Acting as an overriding influence upon this axis are environmental factors such as daylength. The effect of daylength is mediated via the pineal gland and melatonin secretion, which governs the equine breeding season and, to some extent, also sexual maturity and development Marusi and Ferroni, 1993 . Under appropriate conditions, melatonin...

The vas deferens

Vas Ductus Deferens

The vas deferens, or ductus deferens, runs from the cauda epididymis to join with the urethra in the pelvic region of the stallion. It is 25-30 cm in length and 4-5 mm in diameter, except, as already discussed, where it widens out to form the ampullae near the urethral junction Gebauer et al., 1974b . The wall of the vas deferens is thick, in comparison with the diameter of the lumen, and there are three layers of smooth muscle fibres the inner oblique, the middle circular and the outer...

The epididymis

Cross Section The Epididymis

Each testis has an epididymis lying over its dorsal aspect. The tail of the epididymis joined to the vas deferens is situated at the caudal end of the testis and the head joined to the rete testis is situated at the cranial end. The epididymis consists of long, highly convoluted tubules measuring up to 45 m Fig. 3.11. Transverse cross-section through the inguinal canal area of the stallion. Fig. 3.11. Transverse cross-section through the inguinal canal area of the stallion. in length and...

The accessory glands

Ultrasound Bulbourethral Glands

The accessory glands are a series of four glands sometimes reduced to three with the omission of the ampulla responsible for the production and secretion of the majority of the fluid component of semen, termed seminal plasma. Different glands are responsible for the secretion of different fractions or jets. The epididymis of the testis is the other minor contributor to seminal plasma. The accessory glands are situated between the end of the vas deferens and the root of the penis Fig. 3.9 ....

The testis

Testis Tissue Diagram Sertoli Cells

The testes are the site of male gamete or spermatozoa production, and the primary site for androgenic hormone production in the stallion. As such, they play a central role in the reproductive function of the stallion Figs 3.13 and 3.14 . The testes are held within the scrotal sacks, outside the abdominal cavity, and suspended from the abdomen by the spermatic cord area and the cremaster muscles. The scrotum in the horse is relatively short and non-pendulous in nature, when compared with that of...

The penis

Glans Penis Stallion

The penis consists of three identifiable parts the roots, the body or the shaft, and the glans penis. In the resting position the penis lies retracted and held within its protective sheath, with the prepuce surrounding the glans penis, which is out of sight Fig. 3.4 . The penis is held in this retracted position by the retractor penis muscle and the bulbospongiosus muscle, which run ventral to the penis along its length. Innervation by the sympathetic nervous system of these two muscles Fig....