Sheep breeding
Desire, ability and stamina of rams
Ken Wilson, formerly of the Agency for Food and Fibre
Sciences
Revised by Nicole McLennan, Agency for Food and Fibre Sciences
Key points
- Onset of puberty occurs when a ram is 23-27 kg regardless of age.
- Desire or libido refers to the ram’s urge to mate and, may be affected by nutrition, age and breeding season.
- Mating ability refers to the ram’s ability to successfully inseminate ewes and, is influenced by age and physical problems.
- Stamina or serving capacity refers to the number of ewes a ram can successfully serve over a given period of time.
- Serving capacity (a combination of libido and mating ability) will have little effect on conception rates provided the ram flock is kept young and healthy, two to three per cent of rams are joined and, the joining period is at least six weeks.
Desire (or libido)
Desire or libido refers to a ram’s urge to mate. It is not a measure of either fertility or mating ability. The onset of libido coincides with puberty and the start of sperm production. Puberty is determined by body weight rather than age. Rams generally reach puberty between the weight range of 23-27 kg. Virtually all rams heavier than 27 kg (regardless of age) will have reached puberty and developed a desire to mate. But it is doubtful that maximum reproductive capacity is attained until some time later eg one to two years of age.
Libido is regulated by the release of testosterone, produced by specialised cells in the testes. Merino rams show libido almost continuously once they reach puberty, however, nutrition and age can have a marked effect on a rams desire to mate. In British breeds there is a marked decline in testis size, semen volume and libido during the non-breeding season.
Under-nutrition will affect sperm production as well as reduce libido. Rams that are losing weight rapidly or are below store condition are most likely to be affected. On the other hand, over-fat rams may also show reduced libido, particularly when required to work in hot weather.
A ram’s desire to mate also decreases with age. Once rams reach six years of age their fertility and to a lesser extent, libido are well and truly in decline. This is generally due to disease related conditions such as brucellosis and arthritis, which increase in incidence with age. For these reasons it is usually recommended that about one third of Merino rams are turned over annually. This ensures the ram flock remains young and vigorous. In practice, Merino rams are commonly used for four to five years, provided they are sound. British breed terminal sires used for prime lamb production may be used for as long as they remain sound.
Ability (or mating ability)
It is not enough for rams to simply be able to mount ewes, they must also be capable of successfully inseminating those ewes. A rams success or otherwise in achieving the desired end result is known as it's mating ability.
Young rams, at their first joining (18 to 24 months), generally have a poorer mating ability than mature rams. The incidence of this inactivity varies between strains, but most inexperienced rams will become sexually active fairly soon after joining starts. Because of inexperience it is recommended young rams not be joined with maiden ewes, and also that young rams be mixed with mature rams for joining to older ewes.
On the other end of the scale, old rams may mount but not serve ewes because of physical problems (eg lameness or arthritis) which may not be detected by a normal physical examination. Other rams may fail to inseminate the ewe because of abnormalities or injury to the penis (eg bent or short penis, or damage from shearing cuts).
Stamina (or serving capacity)
Stamina or serving capacity is a combination of libido and mating ability and refers to a ram’s paddock mating performance. Rams that have a high serving capacity will successfully serve a large number of ewes over a short period of time (ie at each oestrus cycle). Although it is possible to measure serving capacity in pen or yard tests, the results may not relate to ram fertility in the paddock.
Some rams produce a lot of lambs while others produce very few. In any group of rams there will always be a wide variation in the serving capacity of individual animals, ranging from very high to very low. However, this will rarely have any effect on conception rates providing:
- the ram flock is kept young and, physically and reproductively healthy;
- a realistic percentage of rams are joined (two to three per cent); and
- the length of the joining period is no less than six weeks.
Acknowledgment
The Lamb Boost Project funded by Australian Wool Innovation produced these notes.
Further information
For further information contact the DPI Call Centre on 13 25 23 (Queensland residents) or (07) 3404 6999 (non-Queensland residents) between 8 am and 6 pm weekdays, or e-mail callweb@dpi.qld.gov.au.
This DPI Note is also published on the DPI's PrimeNotes CD-ROM.
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
File No:SW0081 • Date created: December 2001 • Reviewed: June 2003
