by
Susan Schoenian
Date of last revision:
09-Mar-2006 16:33
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Sperm production takes about 49 days. |
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The ram is the most important member of the flock, yet often the most neglected.
Preparing a ram for breeding starts well in advance of the breeding season.
You should never wait until the last minute to purchase rams. You should purchase
rams at least several months before the breeding season. Rams need time to get
acclimated to their new surroundings. You need to start them on the diet that
they will be consuming during the breeding season. Proper management of rams
will go a long way towards ensuring a successful lambing season and profitable
sheep operation.
Age at Puberty
Puberty is the age at which the reproductive organs become functional and secondary
sex characteristics develop. Most ram lambs reach puberty between 5 and 7 months
of age at 50 to 60 percent of their mature weight. The onset of puberty is affected
by breed and nutrition. Ram lambs on a low plane of nutrition may not reach
puberty until they are 12 months old. Some breeds (e.g. prolific breeds: Finnsheep,
Romanov) reach puberty earlier than
other breeds.
Spermatogenesis
Sperm production takes about 49 days (7 weeks) in rams. Testicle size is a good
indication of sperm producing ability. Palpation of the epididymis is a useful
guide for determining sperm reserves. A large, firm tail is indicative of good
reserves whereas a small, soft tail would indicate the opposite. Nutrition can
have a dramatic effect on testicle size. Research has shown that improving nutritional
intake during the two-month period before breeding can increase testicle size
and subsequent sperm production up to 100 percent.
For normal sperm production to occur, it has to be at a temperature several degrees below normal body temperature. The ram has large sweat glands in the skin of the scrotum and a system of muscles that raise or lower the testes into the body for temperature regulation. If the temperature in the testes cannot be kept low enough, due to hot weather (e.g. over 90°F for long periods of time or short spells of very high temperature, 100°F or more), the production of viable sperm will be affected. Fully developed sperm are less affected by heat stress than sperm in the developing stages.
The prevent heat stress, rams should not have a full fleece during the breeding season. They should be sheared 6 to 8 weeks prior to breeding. Adequate shade and water should be provided during the breeding season. In extreme circumstances, rams can be housed during the hottest part of the day.
Seasonal
Effects on Reproduction
Sheep native to temperate climates are seasonal in their breeding habits, though
rams are less affected than ewes. A ram's testicular size, sperm production,
and mating capacity will vary according to the season of the year, being highest
during the normal fall breeding season. Some breeds are aseasonal: Dorset, Rambouillet,
Merino, Polypay, Finnsheep, Romanov, and hair sheep. Temperature is also a seasonal
component affecting fertility in the ram. As little as a half degree change
in body temperature may reduce spermatogenesis and/or libido.
Mating
A ewe in heat (estrus) will seek out the ram. She will sniff and chase after
him. The ram responds to urination by the estrus ewe by sniffing, extending
the leg, and curling his lip. Curling the lip is called the "flehmen response."
If the female is receptive, she will stand for mating. The ram may fail in several
initial attempts to mount the ewe. He may repeatedly mate the same ewe. Rams
will tend to select older ewes over younger ewes and sometimes will choose ewes
of their own breed over ewes of another breed.
Some producers prefer to use one ram per group of ewes. If more than one ram is used, the older ram(s) will dominate the younger ram(s) and may prevent the less dominant ram(s) from breeding. The rams may fight at the expense of mating ewes. It will be more difficult to detect infertile rams or male-oriented rams in multi-sire situations. In large flocks, multi-sire matings are usually necessary. On the other hand, single-sire matings run the risk of low conception rates or an extended lambing season if a ram with reduced fertility or libido is used.
 Long Wool Rams in Maryland |
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Breeding
Soundness Exam
The purpose of a breeding soundness exam (BSE) is to evaluate a ram's potential
breeding ability. There are very few sterile rams, but many rams have reduced
fertility. Research has shown that 10 to 15 percent of rams that are given a
BSE fail or have questionable fertility. A BSE should be conducted by a veterinarian
or trained technician. The exam consists of two parts: physical examination
and semen evaluation.
The ram should be evaluated for lameness, body condition, and any other defects which would interfere with the breeding process. Rams need to be free from footrot or foot scald, and if necessary have their hooves trimmed. The general health of the ram should be evaluated, observing the eyes, feet, legs, prepuce, and penis for any defects that would interfere with breeding. The testes and epididimides should be palpated. A testicle that has scar tissue or is abnormally small will reduce the breeding capacity and endurance of the ram. Swelling of the epididymis could be an early indication of epididymitis (Brucella ovis).
Scrotal circumference (width of the testicles at the widest point) should be measured as it gives a good indication of a ram's breeding ability. Sperm production is directly correlated to testicular width. Scrotal circumference will vary with season and body condition, but should be at its maximum peak during the fall breeding season. Ram lambs with a scrotal circumference of less than 30 centimeters and adult rams with a scrotal circumference of less than 31 centimeters should probably not be used for breeding. There is some evidence to suggest that rams with larger testicles will sire more prolific ewes.
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Scrotal
circumference is a good |
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Semen samples can be collected using electro-ejaculation or via an artificial vagina. Usually veterinary assistance is required to collect semen. Semen should be evaluated for sperm motility, morphology, and white blood cells. The minimum acceptable standards are fair gross motility or 30 percent individual motility and 70 percent normal morphology. White blood cells in the semen are an indication of infection (e.g. epididymitis).
A BSE does not include an evaluation of a ram's sex drive or breeding behavior.
Libido
The willingness to breed ewes is highly variable among rams and can have a major
impact on sheep production, especially in a single sire mating scheme. Libido
is a ram's desire to mate. It is regulated by the release of testosterone, produced
by specialized cells in the testes. Some breeds of rams show libido almost continuously
once they reach puberty. In other breeds, there is a marked decline in libido
during the non-breeding season. Underfed and overfat rams may show reduced libido.
A ram's desire to mate also decreases with age and disease conditions, such
as arthritis.
Some rams have inheritantly poor libido. Studies have shown that up to 15 percent (average of 8 to 10 percent) of rams are homosexual and will not mate with ewes. Unlike heterosexual males, male-oriented rams do not experience an LH surge when exposed to estrus ewes. They also have a reduced capacity for producing testosterone. Animal scientists are hoping to develop a blood test which will identify rams that will not mate with ewes. There is some evidence to suggest that rearing rams in an all-male environment may have a detrimental effect on mating behavior.
A "serving capacity test" can be conducted to determine a ram's desire to mate ewes. In a serving capacity test, rams are exposed to estrus ewes, and their breeding activity is recorded over a period of two weeks or more. Research has shown that a serving capacity test is useful for identifying low and high-performing rams. Ram serving capacity may be affected in utero by number and sex of siblings. Rams born as co-twins were shown to have the highest serving capacity and single born rams the lowest. In another study, long-term selection for reproductive rate in ewes did not affect mating behavior in male offspring. However, serving capacity or breeding behavior is a heritable trait.
 75% White Dorper Ram Rams with strong libidos will get more ewes pregnant and produce more offspring. |
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The
simplest way for a producer to evaluate mating behavior is by observing breeding
performance as rams are exposed to ewes. The use of brisket paint or a marking
harness can be used to monitor breeding activity. If a ram fails to mark ewes,
he should be replaced. The color of the paint or marking crayon should be changed
every 16 to 17 days, starting with the lightest color first. If a high percentage
of ewes re-mark after the first 16-17 day heat cycle, the fertility of the ram
should be questioned.
Ram
Management
A ram may lose up to 15% of his body weight during the breeding season. Consequently,
rams need to be in good body condition at the time of breeding (condition score
3 to 4). Thin rams (condition score 1 or 2) may have difficulty getting the
ewes bred, while fat (condition score 5) rams may be too lazy to breed and their
fertility may be affected during periods of hot weather. Rams should be sheared,
treated for internal parasites, have their feet trimmed, and be started on the
diet that they will be consuming during breeding 2 to 4 weeks prior to breeding.
Rams should be included in the flock vaccination program.
Ram
to Ewe Ratio
The number of ewes that a ram can breed in a 34 or 51-day breeding season
varies according to the age and breeding experience of the ram, the terrain
in which the ram is working, the size of the pasture, and the number of ewes
that will be cycling at one time. A ram can usually mate 3 to 4 ewes per day.
In general, the recommended ratio for mature rams is 1:35 to 1:50. In large
flocks, the percentage of rams to ewes is often higher. Ratios of 1:100 or 1:150
are not uncommon. If estrus has been synchronized, more ram power is needed,
1 ram for every 5 to 10 ewes.
Using
Ram Lambs for Breeding
A ram lamb at 5 months of age will settle some ewes, but he will be a much more
aggressive breeder by the time he is 7 or 8 months of age. As a general rule
of thumb, ram lambs should be 50 to 60 percent of their mature weight before
being used for breeding. Ram lambs should be fed separately from mature rams.
Ram lambs and mature rams should never be run together in the same breeding
group. The older ram(s) will be more dominant and may injure the younger ram(s).
Ram lambs should be observed closely to monitor their breeding behavior and
libido to ensure they are servicing and settling ewes.
 White Dorper ram lambs in North Carolina |
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According to research, 7 to 8 month ram lambs will settle more ewes than 5 to 6 month old ram lambs.
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The
Ram Effect
The
"ram effect" is when non-cycling ewes are stimulated to ovulate by
the sudden introduction of a ram or "teaser." Rams produce a chemical
substance called a pheromone, the smell of which stimulates the onset of estrus.
When ewes and rams are in constant contact (sight or smell), the pheromones
are much less effective at inducing estrus. Ewes that are not cycling when a
ram (or teaser) is introduced will ovulate in 3 to 4 days. This first ovulation
will be a "silent" heat, which cannot be detected by the ram. Following
this silent heat, there will be two normal estrus peaks, with some ewes cycling
around day 18 and the remainder around day 25. Ewes that do not conceive at
either of these times may return to heat in another 17 days. It is expected
that 60 to 70 percent of the ewes will conceive at the first normal estrus.
Of the remaining ewes, 60 to 70 percent should conceive at the second estrus.
Although recommendations vary, rams should be isolated from ewes for at least 6 weeks in order for the ram effect to work. Ewes must have no contact with rams by either sight or smell, which means that they must be separated by distance. The ram effect is not as effective with ewe lambs. The ram effect is most effective during the transitional period when ewes have not begun to cycle, but are almost ready to. Breed of ram can affect ewes' response to the ram effect, with the less-seasonal breeds being more effective at bringing non-cycling ewes into estrus.
The great value of the ram effect is the synchronization of estrus activity which will result in large numbers of ewes ovulating, conceiving, and lambing in a relatively short period of time. To be effective, it is important to have adequate numbers of young, healthy rams. Teaser (vasectomized) rams or testosterone-treated wethers can also stimulate the ram effect.
Causes
of Ram Infertility
There can be many causes of infertility in rams: e.g. poor semen quality, poor
libido, physical defects, disease, poor nutrition, injury, heat stress, obesity,
and age.
Epididymitis due to Brucella ovis is a common cause of ram infertility. The disease usually affects the tail of the epididymis (the bump at the bottom of the testicle) which becomes hardened and swollen. Transmission is from ram-to-ewe or ram-to-ram. Infected rams usually produce semen of lower quality, making them either sub-fertile or sterile, depending on the site and severity of the lesions. Epididymitis can be diagnosed by scrotal palpation, blood test, or semen evaluation. There is a commercial vaccine for epididymitis. Its use is recommended where the risk of epididymitis is high.
Pizzle (or sheath) rot is an infection in the sheath area and could affect breeding activity. Pizzle rot is caused a bacteria, Corynebacterium renale (or one from that group). The other factor is high protein diets (>16 percent crude protein). Ammonia, produced by excess urea in the ram's urine can cause severe irritation and ulceration of the skin around the preputial opening. The debris from the ulcer form a crust which may block the opening to the prepuce.
Click HERE to read an article about Pizzle Rot from the Ontario Ministry of Agriculture.
Cryptorchidism is the failure of one or both testes to descend into the scrotum. Cryptorchids are undesirable breeding animals. If both testicles are affected, the ram is infertile. If only one testical is affected, the ram may be fertile, but he will pass the trait onto his offspring. In contrast, a "short-scrotum" ram is a ram whose testicles have been elevated to the body cavity using a rubber ring. Short-scrotum rams have performance advantages over wether lambs and are easier to handle than intact ram lambs.
Rams reach their peak breeding performance when they are about 4 years old. In commercial situations, they should be culled by the time they are 6 years old. Older rams can be used for hand mating small numbers of ewes.
The Male Reproductive System
Scrotum
- Muscular sac housing the testes. Acts as a thermoregulator.
Testes - Primary sex organ. Sperm production occurs within the seminiferous
vesicles. Production of testosterone occurs in the Leydig cells.
Epididymis - Carries the sperm from the testicle to the vas deferens.
Sperm continue to develop (mature) in the epididymis and are stored there.
Vas Deferens - Muscular tube carrying sperm from epididymis to the urethra
during ejaculation.
Spermatic Cord - Each testes is suspended in the scrotum by the spermatic
cord. Has role in thermoregulation.
Seminal Vesicles - Adds fluid and nutrients to the semen.
Prostate Gland - Produces an alkali secretion to raise the pH of the
ejaculate to about 6.0. Acts as a buffer. Produces characteristic odor.
Bulbourethral Glands - Secrete thick mucous to assist in lubrication
at mating.
Urethra - the joint excretory canal for urine and semen.
Penis - Function is to deposit semen in the female reproductive tract.
Sheath (prepuce) - Fold of skin that surrounds the free end of the penis.
