A long-term program to improve flock reproductive performance at Tom’s Lake merino stud has yielded outstanding results for the Crossley family at Booligal, according to Rob Crossley.

Twenty-five years ago, Rob’s father Jim Crossley decided that if other livestock industries were selecting for reproduction then it would be beneficial to apply this to merino flocks. “You only had to look at how merinos compared to crossbreds to realise that there were gains to be made in lamb-marking percentages. We believed there had been too much focus on other traits to the exclusion of fertility,” explained Rob Crossley.

“Naturally, when choosing to select for reproductive traits we were worried we would end up culling our best sheep on other attributes. And in fact this did happen for the first few years.

“We experienced what we call the tick curve. For the first couple of years, the quality of the flock did stagnate or fall backwards, but once the fertility selection started impacting and lifting our lambing numbers we found we had so many more animals to select from that our culling percentage could increase, enabling the flock to race ahead on other traits.

“Whether micron, fleece weight or body weight – it doesn’t matter.  If you have more sheep to select from you get to any selection criteria goal more quickly.”

In addition, the extra lambs meant more to cull and more to sell, further lifting profitability of the enterprise. “Naturally with the extra lambing percentage, the stocking rate of ewes is slightly reduced but this is more than compensated by the increased surplus sheep sales and genetic gain,” said Rob Crossley.

The Crossleys began by simply wet and drying ewes at lambmarking, and ewes that had dry teats or had lambed and lost were automatically culled, with no second chances. This was quite difficult as it meant a lot of animals with other favourable attributes were culled. This is why the quality of the flock decreased over the first few years.

By wet and drying ewes (and culling dries) the following traits were selected:

• Fertility – the percentage of ewes that get in lamb

• Fecundity – the percentage of twins

• Lamb survival

• Mothering ability – selecting ewes that could defend their lambs from predators and the elements and those that don’t walk away from lambs after birth

• Reproductive soundness – ewes that get a cut vulva at shearing and cannot get served by the ram are culled and those that get cut teats preventing lambs from milking are also culled as they can’t rear a lamb.

According to Rob the process can be particularly hard for those with self-replacing flocks with very low lamb-marking percentages as the number of sheep culled for being dry, lambed and lost, cast for age, or dead or missing, is greater than the number of ewe lambs weaned. Before selecting for better flock reproduction, it is essential to sort out nutritional shortfall, management problems and predators, and get to a reasonable lamb-marking percentage. Producers can move more slowly towards increased fertility by giving dry ewes a 'second chance' before being culled.

Currently the 700 stud ewes are scanned but twinning ewes receive no favourable treatment. They are separated only so twin lambs can be identified and tagged.

In 2007, scanning of the stud indicates 98% fertility (2% scanned empty) 70% fecundity (70% twins, 28% singles). At lamb-marking in 2006, Tom’s Lake achieved 118% in the stud flock and 114% in the commercial flock from 139 mm of rain with no hand feeding. This is compared to about 75%-80% (estimated 94% fertility and 30% fecundity) 25 years ago (average rainfall 300 mm). The stud is ahead of the flock as Tom’s Lake runs an open stud, so better ewes move up to the stud from the flock and vice versa.

“Because of the run of poor seasons, the fertility genetics have not been as expressed as well as they would in an average or good year. We are waiting for an average season to see how much gain has been made and how much the drought has effected the lambing and joining results,” explained Rob.

At sheep-classing time, borderline animals are kept if they are from a maiden ewe or born a twin, but culled if from an older ewe or born a single, as they have had a harder time, and their phenotype (how they look) doesn’t match their genotype (genetics).

As a next step, the Crossleys are looking at mothering up software. This will let them see which of the twin scanned ewes have raised a twin or a single. This will further increase the mothering ability of the flock and reduce the number of lamb losses between birth and lamb-marking.

The process of wet and drying culls ewes that don’t rear a lamb and keeps a ewe that rears at least one lamb, but it doesn’t identify ewes that lose one and rear one of those twins.

“We believe that ewes that rear both twins are more likely to rear both the following year if twins are conceived. So we believe that there is genetic benefit for mothering ability from selecting ewes that raise twins and lambs that have been raised as twins,” explained Rob.

Tom’s Lake is one of the oldest merino flocks or studs in operation to have been selecting for fertility. They currently run 700 stud ewes and 2000 flock ewes, and would normally run a cattle trading enterprise as part of the property. The DSE stocking rate is approximately a quarter of the average rate because of the ongoing drought.

Rob is happy to talk to other producers who would like to increase their fertility and can be phoned on (02) 6993 8250.