Bull Anatomy 101

Understanding bull anatomy will help you recognize common problems and solutions, especially if aspire to naturally breed your own bulls. 

Studying the anatomy of an animal calls for analyzing its life-supporting systems, including the skeletal, muscular, nervous, digestive, endocrine, respiratory, circulatory, and reproductive systems.

In this post, we will restrict ourselves to the bovine male reproductive system. 

As a farmer raising cattle on a small farm, there are several reasons to want to understand the reproductive anatomy of a bull. 

For one, you’ll want to know what the reproductive system of your beef bulls looks like, what problems may affect it, and how you could solve them. 

Knowing the reproductive tract of the bull well also helps you understand breeding soundness and impairments, which is helpful if you plan to breed naturally using bulls. 

Anatomy and Physiology of the Bull

The basic anatomy of the bovine male reproductive tract can be grouped into three: the testicles, three accessory sex glands, and secondary sex organs.

The bull’s reproductive system works to achieve the production, maturation, transportation, and finally, the transfer of spermatozoa from the bull to a cow.

Let’s look at the nature and functions of each part below. 

Testicles

The testicles or testes are conveniently situated outside the bull’s body cavity in the scrotum to make the production of sperms possible at 4-5 degrees below the bull’s prevailing body temperature. 

The testicles fulfill two functions: production of spermatozoa; and production of testosterone—the male hormone. 

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Besides physically protecting the testicles, the scrotum helps regulate temperature to ensure optimum spermatozoa production. 

The scrotum has three structures that work together to control the temperature for a conducive environment for sperm production. The tunica dartos, or the temperature-sensitive muscle in the scrotal walls, contracts when it’s cold and relaxes when it’s hot. 

The second scrotal temperature control structure is the external cremaster muscle inside the spermatic cord. The muscle controls how near or far the testicles are from the main body by shortening when it’s cold in the environment and lengthening when it’s hot. 

The third structure is the pampiniform plexus, a testicular venous network that makes it possible for the occurrence of a blood flow process for counter-current temperature exchange. During the process, arterial blood flowing into the testicles is cooled by transferring the heat in it to the blood flowing out of the testicles through the veins. 

The spermatozoa form and start their maturation in the seminiferous tubules, a collection of miniature, long, and coiled tubes inside the testicle. 

The seminiferous tubules unite to form several larger tubules that branch into the epididymis from the testicle. 

The production of the male hormone testosterone happens in the interstitial cells, which are highly specialized cells lodged in the loose connective tissue that surrounds the seminiferous tubules. 

Sometimes during the development of the embryo, one or both testes fail to lower into the scrotum and remain lodged in the body cavity—a condition called cryptorchidism.

Since cryptorchidism is inherited genetically, you should avoid using a cryptorchid bull for breeding because it is usually subfertile, even though it can produce hormones almost like a normal bull. 

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Secondary Sex Organs 

The secondary sex organs of a bull include the epididymis, vas deferens, and the penis. 

Epididymis

A flat and elongated structure measuring 6-8 inches called the epididymis is attached to each testicle on one side. The epididymis has three distinct portions—the tail, body, and head. 

The tubules that branch down from the testes enter the epididymis head and form a 130-160 foot convoluted tubule stashed inside the epididymis. 

The epididymis is responsible for four crucial functions. Developing sperm cells transport via the epididymis to the ductus deferens from the testicles. The concentration of sperms through the absorption of excessive fluids also happens in the epididymis. 

The developing spermatozoa mature in the epididymis, and the viable ones are stored in the tail of the epididymis. 

Since it is the outlet for the sperm cells manufactured in the testes, temporary or permanent blockage or alteration of the epididymis can cause temporary or permanent sterility. 

Temporary sterility happens during epididymitis—the temporary blockage of the epididymis caused by an infection or injury. 

Vas deferens

The vas deferens or ductus deferens is a straight tubule that starts from the epididymis tail and becomes a portion of the spermatic cord that passes into the body cavity through the inguinal ring. 

The smooth muscle that surrounds the vas deferens contracts during ejaculation to transport the spermatozoa to the pelvic area. 

If you want to raise beef bulls only rather than breeders, you can have your bulls sterilized through vasectomy, where a part of the ductus deferens is cut off. 

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The semen carrying the sperms passes through the urethra, a narrow channel formed when the pair of vas deferens unite to form a single tubule. The urethra also serves as the exit route for urine that must be passed via the bull’s urinary tract. 

Penis

Bulls have a fibroelastic penis held in the S-shaped position by the retractor muscles. Except when the bull is servicing a cow, the sigmoid flexure helps keep the penis in its sheath. 

The purpose of the penis is insemination. When the bull is sexually aroused, the spongy material inside the penis fills with blood to make the penis erect and ready for penetration. 

The glans penis is the end part of the penis that has a high concentration of nerves. Copulation stimulates these nerves and ejaculation is induced, and semen carrying spermatozoa is deposited into the reproductive tract of the cow. 

Accessory Glands

The three accessory glands in a bull are the seminal vesicles, Cowper’s glands, and prostate gland.

The seminal vesicles and prostate gland are found where the urethra forms from the two uniting vas deferens. Their secretions form most of the liquid semen and activate the sperms to make them motile

The Cowper’s glands or bulbourethral glands found on each side of the urethra largely produce a clear and thick secretion that flows out of the penis shortly before ejaculation. The secretion cleanses the urethra by flushing out any urine that may have been left behind, which could harm the spermatozoa.

Alex

Alex grew up in a rural area with chickens, cows, goats, and rabbits. He has always enjoyed waking up at 6 am to tend to his flock and vegetable garden. He bought his first cow at 25 and named her "104". In 2021, he set up an aquarium and now spends his lazy time watching his fish. He is happiest watching small animals and plants grow big, not to mention writing to share his farm-life experiences.

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