Sheep breeding
Ram culling and replacement policy
Ken Wilson, formerly of the Agency for Food and Fibre
Sciences
Revised by Deborah Maxwell and Dr
Roger Lewer, Agency for Food and Fibre Sciences
Key points
- Once rams reach six years of age their fertility, libido and serving capacity can decline significantly.
- Culling rams at a maximum of six years of age is a sound policy. It is a compromise between practicality, maximising genetic gain and economics.
- Rams need to be examined annually for reproductive and physical soundness and those with testicular abnormalities or permanent physical disabilities should be culled.
- Rams should be physically examined before replacements are ordered so that actual replacement requirements are known.
- Stress of any description is capable of rendering rams temporarily (minimum of eight weeks) infertile. Non-locally bred rams will need to be given additional time to acclimatise to their new environment. This needs to be allowed for when purchasing replacement rams.
Culling for age
Once a commercial flock ram reaches six years of age, his best days are normally well and truly behind him. Rams older than this often suffer from impaired fertility and/or reduced libido (sex drive).
As most rams are purchased to be first joined at 12-18 months of age, they should ideally be culled and replaced after a maximum of four years use. This is a sound ram replacement policy to adopt for a number of reasons:
- Age is a good indicator of reproductive ability.
- Culling for age and purchasing replacement rams each year means that a good balance of mixed aged rams is maintained.
- Studs will be in a much better position to supply the quantity and type of ram required if annual replacement numbers are relatively constant.
- Annual replacement of 25 per cent of the ram flock will allow for more accurate budgeting and will place less strain on the bank account than would periodic purchases of large numbers of rams.
Another factor to be considered is the rate of genetic improvement. If your stud is making genetic gain, then each year’s ram drop will be an improvement on the one before. Therefore, the more rapidly that your ram flock is replaced the closer your flock will be in genetic merit to your stud.
Culling for reproductive and physical abnormalities
Rams should be physically examined and testes palpated before annual replacements are ordered so that those with abnormalities (there will nearly always be some) can be replaced. This should be done well before joining to allow replacements a minimum of eight weeks after arrival to recover from any stress related fertility problems arising from their handling, transport and relocation.
Rams of all ages are prone to the development of testicular lesions and abnormalities and need to be examined for reproductive soundness at least once a year, with defective rams being culled.
They should also be checked for general physical fitness and rams with permanent disabilities (eg broken mouth) should be culled. While those rams with problems of a temporary nature (eg lameness, blindness) could be put aside for use the following year, providing they are young enough and otherwise healthy enough to warrant such action.
Get replacements early
Ram fertility is maintained in a very delicate balance. Even slight rises in body temperature for short periods of time can severely disrupt the formation of viable sperm. Stress often results in raised body temperature and is therefore a common cause of temporary ram infertility.
Mustering, yarding, transporting and shearing are all stressful situations that are associated with taking delivery of rams. When taken individually, they are each capable of adversely affecting fertility. When they are combined over a short period of time, the likelihood of fertility problems occurring is much greater.
Although fertility may not always be adversely affected through handling and transportation, it is always preferable not to take chances. Rams suffering temporary infertility will appear quite normal and their ability to work will not be affected. However, the ewes they serve will not get pregnant and they will only compete with fertile rams for the very short period of time that ewes are actually in heat during joining.
Since locally bred rams are already adapted to your environment, any fertility problems associated with their delivery will be relatively short lived. But it can take up to eight weeks before viable sperm is produced. This of course means that rams should be delivered no later than eight weeks before the intended date of joining.
Non-locally bred rams that come from a less harsh environment are much more likely to be affected and can take six months or more to adapt to their new surroundings and grazing conditions. It is therefore important to think well ahead when purchasing rams from an environment that is less harsh than that in which they will be expected to perform.
The amount of time required for rams to become acclimatised to their new surroundings will depend on the degree of environmental change that is experienced. For example, rams from some areas of southern Queensland may adapt more quickly than rams from some areas of New South Wales.
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: SW0076 • Date created: January 2002 • Reviewed: June 2003
