Joining time for breeding sheep

Joining time for rams and ewes should be timed so that there will be good-quality feed available during lambing and lactation, which is usually dependent on seasonal rainfall probabilities.

There are 2 main joining periods in Queensland:

  • autumn (March to May)
  • spring/summer (October to December).

Autumn joining

Where seasonal rainfall distributions allow, an autumn joining is the best option.

If the probability of winter rainfall is relatively high, it's the most successful time because:

  • ewes are joined during their natural breeding season when oestrus activity is highest
  • sheep are likely to be in good condition
  • the worst of the summer heat is over, and gestation coincides with the cooler months
  • lambing takes place before the onset of the summer heat
  • ewes lamb on good to reasonable quality feed.

The peak period of oestrus activity (breeding season) in ewes of all breeds occurs in autumn, when the hours of daylight decrease.

Apart from making maximum use of the ram effect, no other stimulation is needed.

Better nutrition

During an autumn joining, ewes and rams will have—in most years—been on good-quality feed following the summer rainfall. Maiden ewes are more likely to attain their minimum joining weights, 75–80% of mature liveweight, and older ewes will have regained condition following weaning. During most years, your rams will only require minimal levels of supplementation to ensure that your rams are in a body condition score (BCS) of 3.5 for joining.

The availability of high-quality feed at lambing is the most important factor in choosing a joining time. If good nutrition is not available in the majority of years, then the practice of autumn joining should be re-evaluated.

Less heat stress

Temperatures are cooler during an autumn joining, which means rams are more active and less likely to experience heat-induced fertility problems.

Heat stress during pregnancy can negatively affect lamb birth weights, growth rate and increase the mortality rate of lamb survival. This problem is less likely to occur following an autumn joining.

Spring/summer joining

A spring/summer joining will have ewes lambing in the autumn. In areas of northwest Queensland that have significant summer rainfall, this is the most likely time of year when good-quality feed will be available.

Joining at this time of year has disadvantages

  • it's not the ewes' natural breeding season (the ram effect can be used to improve pregnancy rates)
  • nutrition is often of poor quality
  • temperatures are high during joining
  • gestation coincides with the hotter months.

Most ewes will not normally cycle during spring/summer. Rams can only stimulate ovulation in most of the British breeds about 6 weeks before the normal onset of the breeding season (for example, early to mid-January).

However, Merino ewes are not strongly seasonal breeders and, providing they are in a reasonable condition—target BCS of 3—they can be effectively induced to cycle using the ram effect. The use of teasers (vasectomised rams) can be used to synchronise oestrous activity in the flock. Pregnancy rates of 90–95% are commonly achieved in a well-managed spring/summer joining.

Nutritional deficiencies

Nutritional deficiencies during a spring/summer joining can be controlled through careful management. Older ewes should be given a chance to have a BCS score of 3 at joining. Your previous year's lambs must be weaned at least 4–6 weeks beforehand—a compact lambing will help with this.

Maiden ewes need to be treated with additional care, as weaners, to give them every chance of reaching the minimum joining weight. Maiden crossbred ewes can be successfully joined at 7–9 months. Maiden Merino ewes should be at 8–12 months or at 75–80% of their mature liveweight for a successful joining. They may need extra supplementation to get them to a minimum weight (or BCS) and be joined with a higher number of experienced rams to compensate for their shorter oestrus period.

Whilst the impact of age on the success of first joining reduces as age increases, maiden ewes should be managed differently from experienced ewes.

Ewes will readily cycle on quite poor-quality feed in response to the ram effect. Rams will usually need to be supplemented for up to 8–10 weeks before joining.

The cause of a large percentage of lamb mortalities is poor nutrition at lambing. Where rainfall patterns dictate, it is better to modify management procedures and be prepared to accept some losses during joining and gestation than it is to risk a disaster at lambing.

Heat stress

Heat stress is the worst aspect of a spring/summer joining. Hot weather can affect fertility and the mating behaviour of rams. This can be overcome by ensuring your rams are well managed, in good condition and carrying no more than 3 months' wool at the start of joining. Summer temperatures will not usually affect ewes unless some additional form of stress occurs (for example, excessive disturbance, fly strike).

Heat stress seriously affects the growth rate of the foetus and the development of the placenta. This results in lambs with a low birth weight and reduced chance of survival. Heat stress can also cause embryo mortalities early in pregnancy, but this is not a major problem unless additional stress occurs.

For areas where there are limited trees and natural shade, you should provide adequate artificial shade wherever possible. Taking advantage of shade during pregnancy (and lambing) is essential. The worst of the heat is usually over by autumn, but temperatures can still be quite high, so you need to ensure newborn lambs have access to shade and water during lambing.

Lambing planner

Use the Government of Western Australia's online and paper-based lambing planner tool to help calculate your joining lengths and dates.