Active healthy rams are essential for good fertilisation rates, especially for high ewe: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 is important for good mating performance and sperm production, which begins eight weeks before mating.
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.
Brucellosis
Brucellosis is caused by Brucella ovis and may be seen as epididymitis in rams. Often undetected, brucellosis reduces ram fertility and hence lambing percentage if enough rams are affected.
Brucellosis is mainly considered a ram problem but occasionally causes abortion or small weak lambs if ewes are infected.
Brucellosis is spread through sexual activity between rams and by ewes acting as passive carriers at mating, passing it on when mated by more than one ram.
Vaccination is no longer practised. Buy rams from accredited brucellosis-free flocks and beware of infection introduced by males other than breeding rams — e.g. a neighbour’s cryptorchid lambs run with the rams while waiting to be collected.
Isolate rams with epididymitis or testicular abnormalities (e.g. hardness or odd sizes) and blood test as soon as possible.
Scrotal mange
Scrotal (chorioptic) mange is a disease which 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
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 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 which 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.
Behaviour and sexual experience
Ram libido and sexual activity vary considerably. Across a range of studies, 27% of the rams used were found to be inactive when first exposed to ewes in oestrus.
While most rams improved with further exposure to ewes, some still showed poor performance — e.g. low libido and low ejaculation rates.
Older, experienced rams usually seek out ewes in oestrus whereas inexperienced rams, especially lambs, may not be as efficient at detecting ewes in oestrus and may have lower fertility.
Use ram lambs at reduced ratios (e.g. 50 ewes per ram lamb) and mate to older ewes which will look for the ram.
Harnesses are useful to show ram lamb activity, especially for single-sire mating.
With high ewe:ram ratios of 150+:1 use experienced rams if possible and avoid large paddocks.
Ram libido may outlast sperm production, so rams may appear to continue mating but prove infertile.
Vasectomised rams
Vasectomies must be done by a veterinarian at least six weeks before use. Vasectomised rams can be used to:
- Stimulate ewes to cycle earlier.
- Identify ewes in oestrus for AI.
- Identify non-pregnant ewes after mating, using harnessed vasectomised rams (e.g. 500 ewes to one ram) after breeding rams are removed. This method identifies non-pregnant ewes for early sale well ahead of pregnancy scanning.
- Stimulate hoggets to cycle earlier.
- Introduce non-breeding hoggets to the vasectomised ram and get them accustomed to ram behaviour.
— Excerpt from ‘‘Making Every Mating Count’’, by Beef + Lamb New Zealand
