Recommendations
• Rams should be checked before ram-buying time, and again eight to 10 weeks before mating. Good feeding and exercise should start.
• Buy rams from brucellosis-accredited flocks and check all rams for testicle abnormalities and mange at least eight weeks before mating.
• Sperm production and semen quality are best in rams with larger testicles and when scrotal temperature is lower than body temperature.
• Use lower ewe-to-ram ratios with younger ewes and/or rams.
Health inspections
Active healthy rams are essential for good fertilisation rates, especially for high ewe-to-ram ratios (100+:1).
Inspect your present rams before ram buying to check the number of replacements needed and again eight weeks before mating.
A quick examination the day before putting the rams out leaves no time to cure health problems or find replacements.
Ram preparation
Eight weeks before mating, check for:
• Wounds and flystrike.
• Genital health problems such as epididymitis, scrotal mange, pizzle rot and penis abnormalities. Isolate any rams with genital problems immediately to reduce the risk of infecting healthy rams. Get your veterinarian to inspect and blood-test these rams.
• Foot problems. Footrot and other lameness may reduce feed intake and hence sperm production, as well as reducing ram mobility during mating. Foot abscess will elevate body temperature and cause infertility for up to two months.
Seek veterinary advice for treatment of genital problems or foot abscess.
Sperm development takes eight weeks, so all sperm present at mating has developed prior to the mating period. Begin good feeding and exercise at least eight weeks pre-mating.
Avoid shearing within eight weeks of mating.
Scrotal mange
Scrotal (chorioptic) mange is a disease that may render rams infertile by raising testicle temperatures.
Mange is associated with infestation by the Chorioptes bovis mite. Dried exudate appears on the skin, revealing damaged weeping skin when scraped from an active lesion.
Many rams carry mites but have no lesions and there is no correlation between mite numbers and the extent of lesions on individual rams.
Rams with small inactive lesions may produce normal semen but rams with extensive lesions have poor-quality semen.
Check rams carefully and reject any with active or extensive lesions — consider them temporarily unsound, treat and re-examine.
Rams with severe active or inactive lesions may be permanently unsound and should be replaced.
The mite may be carried by other animals (e.g. horses, cattle and goats). Consult your veterinarian about a treatment programme if rams have problems with scrotal mange.
Sperm production and testicle size
Sperm production is proportional to the amount of testicular tissue — i.e., rams with larger testes generally produce more sperm.
Large testes and high sperm production allow sperm numbers to remain high when rams serve many ewes per day. Testicle size may thus indicate a ram’s potential ability to serve large numbers of ewes, although sperm quality, ram mobility and libido are also important. This recommendation is for ram breeders only.
Simple practical measurements such as scrotal circumference can be used to estimate testicle weight and hence sperm production to compare rams for likely serving capacity. Generally, a scrotal circumference of 30cm or greater is adequate.
Scrotal temperature
The testes must remain cool for the best sperm production and survival.
This is especially important in the last eight weeks before mating, as fever or stress from any cause may reduce sperm quality and/or quantity.
If rams are in full wool it is advisable to shear the scrotum and crutch, and in hot areas shade should be available for rams.
Seasonality
Decreases in semen volume, sperm density and motility have been noted during late spring and early summer (i.e. when seasonal sheep breeds are sexually inactive), with peak values during autumn. In practice these changes are not usually important.
Semen quality
Semen quality tests are not warranted with commercial rams. Quality is most likely to be checked with expensive rams used by ram breeders in single-sire group mating.
Semen collected using electro-ejaculation is suitable for checking sperm motility and morphology but sperm numbers are variable and this is not a good check for density.
Samples collected with an artificial vagina are generally more consistent and sperm density tends to be higher.
Two or three tests at five-day intervals are a better predictor of fertility than a single test. If any factor is unsatisfactory at the first test, repeat testing before rejecting the ram.
Sperm volume and density also decline after frequent ejaculation, so testing after high levels of sexual activity may give misleading results.
High-serving capacity rams
Identification of high-serving capacity rams is best done with a serving-capacity test that measures the number of successful services within a given period of time (e.g. two or more ejaculations when confined in a pen with four oestrus ewes for 20 minutes).
Testicle size, as mentioned above, indicates likely sperm production and possible serving capacity.
Rams born to prolific ewes, and preferably born as twins or triplets themselves, are more likely to have a high serving capacity than rams born to low-fecundity ewes.
Rams born as co-twin to another ram are more likely to have a high serving capacity than rams born as co-twin to a ewe lamb.
