Fertility and Sterility in the Buck
Reviewed by Dr. William Holleman
Sterility in the buck is usually the exception rather than the norm and is usually temporary. Male fertility is affected by such things as age, maturity, nutritional status, general health, endocrine balance and normality of sex organs. Sperm quality , nutrition, body weight, maturity, stress, disease, mating frequency, seasonal and climatic changes, and management also play roles in male fertility. With so many things affecting fertility, it's a wonder that sterility is rarely a problem.
A buck kid starts mounting behavior as early as one day old. Puberty, the age at which spermatozoa is present in the ejaculate, can vary depending on breed, age and nutrition. Pygmy bucks are capable of breeding as early as 8-12 weeks of age, and they are one of the most outwardly sexually aggressive animals I've treated.
From the time of birth the male body begins to changing to prepare them for this experience. A buck is born with his urethral process and glans penis adhered to the inside of his sheath (prepuce) by the frenulum membrane. This adhesion makes it impossible for the buck to copulate until testosterone (a steroid) and practice mounting frees penis from the prepuce. He will then be able to fully extend his penis and copulate.
As this takes place, the buck kid will start urinating on front legs and beard and develop a strong odor. Part of his odor is due to the urine, but mostly it is a result of the the influence of testosterone on the scent glands located near his horns. This behavior and odor make the buck more attractive to females and stimulates their estrus and receptivity.
The blubbering noise and behavior is one of the buck's comical displays. In the early 1990s, someone won $10,000 on the television program, America's Funniest Home Videos showing this behavior. To a buck, this is serious business. He may paw the ground, wet on his chest and forelegs and exhibit mounting and thrusting behavior. He may nudge the doe and lick her genitalia and smell her urine. This precedes another comical action called flehmen in which the buck raises his head and curls his upper lip in odor detection mode; it looks like he is smiling. All of this usually occurs very quickly with a cooperative doe, and a successful breeding occurs when the buck mounts and ejaculates. Ejaculation is best confirmed by the buck's head jerking back immediately before he dismounts. The doe may react by moving her hindquarters forward, and a drippy discharge can usually be seen coming from her vulva.
To increase the volume of semen and concentration and number of
the sperm, you can put the buck on a lead and allow him to make a few false
mounts on the doe before he ejaculates. This may not work with all bucks, but it
is sometimes done with great success in semen collection.
How the Reproductive System Works
Each intricate part of the buck's reproductive system has one or more function, and every one must operate properly for the whole system to work. The following is a brief description of the major parts and the roles they play.
The major function of the testes is to produce high quality sperm. Muscle contractions help sperm move from the testes into the ductus (or vas) deferens. From there the sperm travel through the abdominal cavity in the ductus deferens to the urethra where it exits the body through the penis. Sperm is stored several paces with various functions. The epidiydymis functions as a maturing station, and sperm are held there for up to 14 days before entering the ductus deferens. During this maturation process, the fertilizing ability and motility of the sperm is increased. When the sperm reaches the ductus deferens, it is mature.
|On the sperm's journey various glands add their secretions. The prostate gland's secretion thickens the semen and helps regulate the acid base balance. The vesicular glands add fructose and citric acid to nourish the sperm. The bulbourethral gland secretes liquid that neutralizes the acidic urethra before the sperm travel along it in an ejaculate. After all the ingredients are added the sperm officially becomes semen capable of fertilization.|
|The penis' S-shaped sigmoid flexure is controlled by contracting muscles and, in turn, so is the erection. Erection is the result of sexual excitement that stimulates blood flow to specific tissues in the penis which increase pressure in the organ and straighten the sigmoid flexture. At the same time, retractor muscles relax and the penis is extended from the sheath. Ejaculation is a nervous system reflex, the result of muscular contractions that begin in the epididymis.|
If the buck fails to ejaculate, one of the first things to check for is a condition known as a persistent frenulum. This membrane usually detaches as a buck matures but rarely it does not. To examine a buck for this, he is set on his rump and the sigmoid flexure is pressed from behind to manually extrude his penis. If you are not sure how to do this or what to look for, your veterinarian can help. Simple corrective surgery can fix the problem.
If the buck fails to impregnate does, it's time to investigate with a breeding soundness examination. This is also a good time to check for the presence of extra teats and other hereditary defects, such as hernias and jaw malformations. A buck with any faulty traits or who is hormonally unbalanced should not be used.
The first thing to look for in the physical exmination is general health. Does the buck look healthy, including a shiny hair coat, clear eyes and nose? Feet, joints and teeth in good condition? Are his temperature, respiration and pule normal? Is he too fat or too thin?
The reproductive organs should be examined next. This includes palpation of the testicles for size, symmetry and other normal values, and inspection of the prepuce and penis. The larger the testicles, for a given age, the better the sperm production. Bucks with above average scrotal circumference for their age and birth weight can be expected to produce offspring with earlier sexual maturity and greater fertility. Scrotal circumference can be measured with a measuring tape and then transcribed to a ruler. The measurement should be taken at the widest part of the scrotum with both testes held at the same level. The scrotum should be firmly attached.
The texture of the scrotum is important. Normal testicular tissue should feel resilient and approximately as firm as muscle. Some problems may be associated with texture and size/swelling. For example, testicular atrophy (marked by abnormal spermatozoa) results in elongation or smaller than normal testes. Abnormally small testes may indicate severe malnutrition or an intersex (genetic) condition.
Bucks occasionally get orchitis, an inflammation in one or both testicles. This soft swelling (no heat) is usually physiologically caused and not infectious. This may have something to do with semen storage in the testicles but if it becomes a chronic problem, the testicles may harden and shrink, causing sterility.
Inspect the prepuce and penis for infection or injury. For example, in posthitis (pizzle rot) the prepuce will be inflamed with ulcerations or scabs and accumulation of urine and dirt. These lesions make breeding too painful or physically impossible. It can take a few days to a few weeks to treat this condition before the buck will be willing to breed.
Collection and evaluation of semen is part of a comprehensive breeding soundness exam. The best semen sample comes from using an artificial vagina, versus electroejaculation. Morphology, numbers, motility (movement) and longevity of the sperm are all important. The normal sperm count in a buck is about 2,000 per millileter. Too many malformed sperm indicate poor quality semen. Very young and very old bucks may have more sperm irregularities, as well as those who are deficient in selenium. A densometer can be used to count sperm, but semen color can give you some indication. Thick, milky semen is good. Thin, milky semen is mediocre and clear/amber semen may indicate poor quality. Sperm motility is difficult to check in collection samples. Physiology and biochemistry of the semen is also important. Semen evaluation is best left to a veterinarian or an experienced qualified semen collector/processor.
If he passes the breeding soundness examination with flying colors but he still not settling does, you need to consider other management possibilities. Is he overweight? Obesity definitely plays a big role in fertility. What are you feeding him? Feeds like timothy grass and clover with high estrogen content may suppress the antigens of a buck and in time the testicles may atrophy (shrink) and feel cold. An emaciated buck can become sterile. In either sex, the reproductive system is one of the first functions to shut down during starvation. Excess fat or thinness can be reversed with better management.
Reluctance or inability to mount may be due to painful hind legs, hips, stifles, hocks or feet, and the cause should be defined. Arthritis seems to be fairly common in older stud bucks. Is it due to excessive calcium in the diet or housing on cold, damp, bedding? All possible causes need to be considered. You can use a buck after injury, when he is healed, and if he is able to work, however, if you suspect a structural fault or disease, further use is not be recommended since he may pass these features. It is best to be very discriminate in propagating any negative traits; the buck is the major part of your herd.
A high fever in a buck can render him temporarily or permanently sterile. Sperm is produced at an optimum temperature, and this process is very sensitive to heat. If the temperature is increased dramatically, it affects the testicles and the quality and life span of sperm. A buck regulates the temperature of the scrotum and testes by controlling the distance they are from the body. When it is cold, the dartos muscle contracts to pull the testes closer to the body. When it is hot, the muscle relaxes and allows the testes to hang further from the body. When a buck has a fever it is almost impossible for his body to maintain the proper temperature for sperm production. Very hot weather can also render a buck temporarily sterile. Remember, the sperm in the ejaculate originated 4-6 weeks ago; what he produces today is a result of what happened way back then. This is an important fact to remember when you are looking for answers to a sterility problem or planning ahead for breeding.. Think in terms of more than just the last several weeks.
Infection may be another cause for sterility. If the penile sheath is injured it is vulnerable to infection. If the sheath is allowed to accumulate sebum (fatty secretion of the sebaceous glands) he may transmit coital vesicular exanthema which creates small ulcers on and around the vulva of the doe. For this and other reasons, cleanliness of the buck is very important, especially in a buck that is used heavily on a large variety of does from a number of herds. In heavy use, the buck's penis should be washed several times a month. The penis can be washed with soapy water, or a 1:5,000 dilution of Nolvasan™. Good hygiene can eliminate several problems that may eventually cause sterility.
Stones can become blocked in the urethra, causing sterility and sometimes death. When a buck or wether has a dietary imbalance of calcium and phosphorus, stones form in the bladder and move through the urethra. The urethra and ductus deferens join near the urinary bladder, so if the urethra is blocked neither sperm or urine will be able to exit the body. This is fairly common in wethers or bucks that are fed too much grain. Partial blockage is also possible. Treatment for this is difficult at best.
Other factors affecting sterility are anatomical defects, and other injuries and diseases. Scrotal hernias are seen in sheep and are presumed hereditary in that species. If a hernia (distention of one side of the scrotum with a movable loop of intestine) is identified and surgical correction is desired, the buck should be castrated.
Injuries or wounds involving the scrotum may result in purulent orchitis or periorchitis. Other causes of scrotal dermatitis include mange, bacterial infections, zinc deficiency and frost bite. Many different types of injuries may take place if two bucks are allowed to be in the same area while one is breeding; common ones are a broken penis and a broken leg.
Sperm granulomas are strongly correlated with the homozygous polled condition and can be avoided by culling all young bucks that are, by phenotype, homozygous for the polled gene. This condition is virtually unknown in the Pygmy, as it is a disqualifying fault in their Breed Standard. Another rarity is the protozoan parasite, Trichomonas. This protozoa has been observed in the semen of Alpine and Saanen bucks in France and Sardinia and in Angoras in South Africa. It infests the sheath and urethra of the buck, causing the quantity and quality of ejaculates, as well as libido, to decrease. Testicular tumors in goats are rare but do occur.
It is possible to overwork a buck, especially when it is undernourished. Special attention should be given to the breeding buck's nutrition. Many bucks ignore their food during breeding season while increasing physical activity, and the attentive owner should vary the diet to tempt him to eat. A frequently used buck will also be less fertile per doe than a buck who has rest periodsbetween services. After around 3 ejaculations the sperm count is reduced, and after 7 ejaculations the buck produces immature sperm that are incapable of fertilization.. Overuse can be hard to determine since bucks can settle a hundred or more does in one season, depending on his condition, nutritional level and general health. It is better to err on the conservative side.
Genetics, nutrition, sanitation and other good management practices play important roles in the buck's life. From birth a buck's body prepares itself for its main function - breeding. It's up to you to make sure that the things you can control, like proper nutrition and a positive environment, are in his favor. After all, he is the single most important ingredients in your breeding program.