The ewe breeding cycle and the 'ram effect'

PRODUCTION ADVICE - OCTOBER 2020 - ANIMAL BIOSECURITY & WELFARE

By Eve Hall
District Veterinarian
P: 0439 078 989 | E: eve.hall@lls.nsw.gov.au

Generally, sheep are ‘short day’ breeders, meaning they tend to naturally cycle best as day length becomes shorter. Different breeds vary in their seasonality, with British breeds such as the Border Leister and their crosses being much more seasonal the Merino or Dorset.

Figure 1. Indicative pattern of natural cycling activity in various sheep breeds throughout the year (Source: O’Halloran 2007)

By the end of January, most ewes are cycling spontaneously every 17 days and a joining period of two cycles or five weeks is recommended.

The challenge lies in joining between now and February, particularly in British breeds and their crosses, during which time there is a lower percentage of ewes naturally cycling. So, how can we improve joining outcomes during this period?

The ‘ram effect’

Complete isolation of ewes from rams before suddenly re-introducing rams will have the effect of stimulating ewes to begin cycling. For this to work successfully, ewes must not have any contact (sight, sound or smell) with rams for at least one month before joining commences. A distance of at least 1km from any ram (including neighbours’ rams) is recommended.

Either rams, testosterone-treated wethers (known as ‘teasers’), or vasectomised rams will produce the pheromones needed to achieve the ram effect.

Usually, the ewe’s initial stimulated cycle will be a ‘silent heat’. For this reason, it’s a good idea, if feasible, to use teaser wethers or vasectomised rams during those first 14 days. This prevents entire rams from becoming frustrated and injuring each other while waiting for the ewes to come into standing heat.

Example use of teasers for a natural mating program:

1. Inject selected wethers with testosterone seven days prior to commencing teasing.
2. Tease for 14 days.
3. After 14 days, introduce rams to ewes at 2 per cent and join for 35 days (teasers can be removed or left with mob – ram-like behaviour from testosterone only lasts 3-4 weeks).

*It is important to note that testosterone-treated wethers cannot be sold – they much be slaughtered on farm or kept for teasing in subsequent years.

What are the main benefits of using the ‘ram effect’?

• Most ewes are cycling when the entire rams are joined
• The joining and lambing will be more compact
• The lamb drop will be more uniform in age and size at marking, weaning and first shearing

Aside from seasonality, other critical factors for a successful joining include:

• Ewe nutrition
  • Nutrition and condition score are the greatest determinants of ewe reproductive rate.
  • Check ewe condition at least a month prior to joining to assess if feeding is required to maintain their condition.
  • Check ewes for low condition, udders, poor feet and mouth condition, and cull appropriately.
  • Aim to have ewes in condition score 3+ during joining.
• Ram preparation
  • Rams should be checked prior to joining for general and reproductive health - carry out the 'four Ts' health check: teeth, testes, toes and tossle.
  • Rams can benefit from a high-protein and energy diet in the eight weeks leading up to joining.
  • Sperm development takes around seven weeks, so avoid any stress, activities or treatments during the eight weeks prior to joining.