It is estimated that the cost of a ewe replacement coming into a flock at 19-months-of-age is equivalent to 25% of the lamb carcass that ewe produces in her lifetime.

This is according to Teagasc’s Tim Keady, who was speaking at the Sheep Open Day in Athenry last week (June 18).

Speaking about improving flock efficiency on the day, Tim said: “Currently, ewe productivity in Ireland is relatively low, at an average of approximately 1.3 lambs/ewe joined on lowland sheep farms.

“And it hasn’t changed a lot in the last 30 to 40 years. In prime lamb production most of the costs are associated with the ewe.

“So if you can increase the number of lambs reared during a ewe’s lifetime, you are reducing the cost/lamb and thus lamb production.

“With this in mind, we set up a long-term study where we wanted to look at replacement cost, with two factors being looked, which were number of lambings, which is age at first lambing and litter size.

“We had two ages at first lambing – either lambing at 12-months-of-age or at two-years-of-age,” Tim continued.

“We used three different ewe genotypes. We had a Suffolk, Belclare and a Belclare-cross Suffolk.

“We chose a Suffolk, because on lowland farms today in Ireland, 50-55% are made up of Suffolk or Suffolk-cross ewes.”

The Belclare was chosen because it represents 10% of ewes in lowland flocks but also because of their prolificacy, Tim added.

“And we crossed the two [Suffolk and Belclare] to see would any hybrid vigour be achieved,” he said.

“When all of these animals were managed from four-months-of-age onwards until they were culled for reasons – such as age [or] mastitis – but they weren’t culled if they were barren.

“For example, when they lambed, they were on a grass-based diet. Ewes that lambed and that reared one and two lambs were offered no concentrate supplementation from the time of turnout to pasture nor did they get any prior to slaughter.

“Ewes rearing three lambs got a half a kilo/day of ration for five weeks post-lambing. Their lambs had access to a creep feeder and were fed 300g of ration up to weaning.”

“Post-weaning, all lambs – regardless of being a single, twin or triplet-reared lamb – were put together as one flock and on a grass-only diet, Tim explaine,

They were drafted every three weeks, with the last draft coming in late November/early December.

“If we look at the lambs performance, firstly as they were lambing down as ewe lambs. The Suffolk on average reared 0.8 lambs, the Belclare-cross Suffolk ewes reared one lamb and the Belclare ewe reared 1.2 lambs/ewe joined,” said Tim.

“In other words, genotype had an effect on the number of lambs reared by approximately 0.4. Lambs were slaughtered at an average carcass weight of 20.4kg.

“If we look at the lifetime performance of the different ewe genotypes, it had little effect on the number of lambings, but it had an impact on the number of lambs reared per ewe joined,” he continued.

“On average, Suffolks reared 5.3 lambs, while Belclare-cross Suffolk ewes reared 6.7 lambs – which was a difference of 1.4 lambs.

“Which equates to approximately €200 at today’s prices which would have covered the cost of a replacement coming into the flock at 19-months-of-age.

“The second factor we looked at was age at first lambing. A question many producers ask is if you lamb at 12-months-of-age, does it have a negative effect on performance at lambing at two years of age?

“Well, a ewe that lambed down as a ewe lamb, produced one extra crop of lambs [4.1 vs 3.2] and also the number of lambs reared differed between age at first lambing of approximately 1.4 lambs/ewe joined – again the equivalent of approximately €200 or another way of paying for your replacement cost.”

Some key factors were noted, one being how weight at seven-months impacts on lifetime performance.

“We found that if you were to increase the weight at seven-months by about 15%, which is approximately 7kg, that you would increase the probability of rearing one lamb by between 10% and 23% at one-year-of-age and it even had a positive effect when lambing down at two-years-of-age of 5-8%,” said Tim.

“The lower figures were for the more prolific ewe genotypes such as the Belclare and the higher figures were for the less prolific ewe genotypes [Suffolk].

“We took an efficiency index called the probability of rearing at least one lamb because it takes into account, ewe mortality and barrenness and lamb mortality.

“We also found that the weight at seven-months had a positive effect on the number of lambs reared in their lifetime, an increase 0.4 lambs reared and it increased the weight of lamb carcass by 18kg.

“If we take the two extremes of the treatments used in the study, a Belclare-cross Suffolk ewe lambing as a ewe lamb produced 57% more lambs than a Suffolk lambing for the first time at two tears of age.”