While lambing replacement ewes at one-year-old is a common practice in many flocks, some farmers prefer to first lamb replacements at two years-of-age.
With good husbandry and nutrition, the College of Agriculture, Food and Rural Enterprise (CAFRE) has said lambing ewe lambs can improve the financial viability of sheep systems and reduce the number of breeding females kept, or bought in, the following year.
Stephen Flanagan, a senior beef and sheep advisor at CAFRE has outlined that breeding from ewe lambs allows for faster genetic progress, optimising live weights, reproductive success, and crossbreed trait benefits.
The success of such a breeding programme involving ewe lambs requires careful weight management and attention to detail.
Ewe lambs need to have reached 60-70% of their mature bodyweight prior to mating, a target that Flanagan said is essential to maximise conception rates and ensure good foetal development.
E.g., breeding from a Texel X Mule ewe lamb with a potential mature weight of 75kg must be between 45-50kg at time of mating.
However, the CAFRE senior beef and sheep advisor said that heavy feeding of very young female sheep (younger than five months-of-age) can reduce mammary gland development and subsequent milk yield.
Ewe lambs can have a lower initial reproductive performance which can be caused by various factors, including the age of the onset of puberty.
While this can occur between 7–10 months-of-age, it can be brought on earlier with the interaction of teaser rams.
If using teaser rams, the teaser should be left in with the ewe lambs for 14 days before fertile rams are introduced.
CAFRE recommends that ewe lambs should mate with ram breeds with a smaller than average mature size and farmers should use breeds with evidence of lower birth weights.
The ideal group size, according to CAFRE, is one ram to 25-30 ewe lambs and grazed in small fields or paddocks.
CAFRE referred to studies that showed lower embryo survival has been demonstrated in ewe lambs when compared to mature ewes in the first 30 days following conception.
To help counteract this, CAFRE recommends that ewe lambs should mate on lower grass heights of poorer nutrition.
This can help slow down the amount of hormones filtered out by the liver which in return will hopefully result in higher scanning results, according to CAFRE.
However, while ewe lambs are recommended to be on lower grass quality, Flanagan said they must be gaining at least 250g/day for a further six weeks post-mating, and then lowered to 130-150g/day up until six weeks before lambing to aid in embryonic survival.
During early and mid-pregnancy, Flanagan said ewe lambs need about 20% more feed than mature ewes of a similar weight to sustain their continuing development.
He urged farmers not to overfeed in the last week before lambing and target feed only for maintenance and pregnancy, not growth.
Feeding for growth at this point, according to the CAFRE advisor, will create large single lambs and potentially increase lambing difficulties.
From an environmental aspect, breeding ewes as ewe lambs can also provide additional benefits, e.g., by reducing the farm carbon footprint.
When using these results within a commercial carbon footprinting tool, CAFRE said the carbon footprint was 5% lower for a system using ewe lambs rather than hoggets.