Joining time for rams and ewes

Joining time for rams and ewes should be determined by seasonal rainfall probabilities, and timed so that there will be good-quality feed available during lambing.

There are 2 main joining periods practised in Queensland:

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

Autumn joining

Where seasonal rainfall distributions allow, an autumn joining gives the best of both worlds. If the probability of winter rainfall is relatively high, it is by far the most successful time to join because:

  • ewes are joined during their natural breeding season
  • 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) for all breeds of ewes is in autumn, when the hours of daylight decrease. Apart from making maximum use of the ram effect, no other stimulation is needed.

Nutrition for autumn joining

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 (around 35kg) and older ewes will have regained condition following weaning. During most years your rams will only require minimal levels of supplementation.

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 in autumn joining

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

Heat stress during pregnancy can affect lamb birth weights, reducing smaller lambs' chances of 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 north-west Queensland that have significant summer rainfall, this is the most likely time of year when good-quality feed will be available. However, there are several disadvantages associated with joining at this time of year, for example:

  • 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 breeding season (i.e. early-to-mid January). However, Merino ewes are not strongly seasonal breeders and, providing they are in a reasonable condition (score 2.5 to 3), they can be readily induced to cycle using the ram effect. Oestrous activity can also be synchronised through the use of teasers. Pregnancy rates of 90-95% are commonly achieved in a well-managed spring/summer joining.

Nutrition in summer/spring joining

Nutritional deficiencies during a spring/summer joining can be controlled through careful management. Older ewes should be given a chance of being condition score 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 a minimum joining weight of 35kg at 18 months of age. For example, they may need some extra supplementation.

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 highest cause 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 in summer/spring joining

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 (e.g. 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 is 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.

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