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Booroola Gene

grazing sheep

Additional Articles

  • Genetic Theory supporting Booroola F+ gene for commercial lamb production - Part 1

  • Twenty Years of Experience with the Booroola F+ Gene in Commercial Lamb Production ... To the right

  • Managing Prolific Ewes and Large Litters...  Part 3

sheep in spring pasture
sheep eating
lamb in pasture

Revisiting the Booroola F+ Gene

Part 2 of 3

 Twenty Years of Experience with the Booroola F+ Gene in Commercial Lamb Production

By Robert Leder, DVM

Our sheep enterprise is a grass based system.  Thirty acres of “aging” grassy alfalfa hay ground is what we started with in the late 1980’s.  Over time we added fences and inter-seeded clovers and more grasses to the land.  We moved an old barn, granary, and workshop to create a farmstead.  This was a slow process so we slowly grew our flock from 10 ewes in 1988 to 72 ewes by 1998 to 90 ewes today.  Because we were aware of the detrimental affects of OPP, we eliminated it from our flock when we started. 

Our system is based on shed lambing immediately prior to the availability of good grazing grass in the spring.  For us, this means starting to lamb in early April.  The earliest lambing ewes get access to grass during the day sometime between the 15th and 20th of April.  By the end of lambing all the ewes and lambs are on grass fulltime in early May.  No grain is fed to the main flock during grazing season.  We realized that the single largest cost of lamb production is feeding the ewe, especially during lactation, and synchronizing lambing and lactation to grass growth would be paramount to profitability.  Limited grain is fed to select groups of pregnant ewes in the winter and during lambing season. 

If we were going to go through the effort of shed lambing, we wanted to maximize the number of lambs per ewe.  We set a goal to wean a 200% lamb crop.  We were intrigued by the possibilities of using the Booroola F+ gene to increase our lamb drop.  Our theory at the time was that it would eliminate the need to incorporate a prolific breed (Finnsheep or Romanov) in our crossbreeding program.  While ewe prolificacy is recognized as only 10% heritable within established breeds according to the SID handbook; incorporating the F+ gene into a population (our flock) would make it nearly 100% heritable.  Simply put, differences in litter size within the flock would be due largely to the presence or absence of the F+ gene.  While the gene would only be transmitted to half of a ewe’s offspring, we believed that would be a sufficient increase to push our lamb drop over 200%.  The recognized prolificacy bump of the F+ gene is 1.2 lambs more per lambing.  So, if half the ewes carry the F+ gene that would increase our lamb crop by 60%. 

Our initial ewes were Oxfords that I purchased from my brother.   The flock had been mine prior to going off to college.  I liked the growthiness, muscling, quite disposition, lamb vigor. and the fact that Oxfords sheared the heaviest fleece of the down breeds.  With a lambing rate of 150-180% we realized we’d need something to boost the prolificacy of the flock to meet our lamb crop goal.  With the majority of our projected income to come from lamb sales, we wanted “prolific meat” sheep.

We acquired the Booroola F+ gene through artificial insemination in the fall of 1988.  The efforts yielded ten Booroola-Oxford cross lambs, 9 ram lambs and one ewe lamb.  While initially disappointed with the sex ratio of the lamb crop, in retrospect it was better we had more ram lambs, because we were able to select the best of 9 rather than 4 or 5.  The dam of the ram lamb we selected was a triplet born, well muscled, good milking old fashioned Oxford ewe.  We used this ram “Jerry” for ten years.

The poor lamb crop sex ratio did spur us to purchase some ewes to cross with Jerry.  We added a couple Oxford cross ewe lambs from Jim Schultz’s flock of commercial crossbred white faced ewes that were sired by our Oxford ram.  Additionally, we were able to buy some of Spruce Shadows Sheep Farm’s (now known as Sheep Improvement Company) last old fashioned Hampshire ewes.  This kept with our goal of producing “prolific meat” sheep, and fit fairly close to the genetics of the Oxfords we already had.  Because we expanded our flock slowly from within, keeping all of “Jerry’s” ewe lambs, half of them would carry the F+ gene.   This ewe base would help set the F+ gene frequency in our flock for years to come.

One of the first adjustments we made to our breeding scheme was spurred by our observation of the ewes coping with mid-summer heat out on the pasture.  Our Hampshire and Oxford cross black-faced ewes did not tolerate the heat nearly as well as the crossbred ewes from Jim Schultz that were speckle faced.  We realized that we should “lighten up the faces” of our ewe flock by including a white-faced breed in our breeding scheme. 

 The first white faced breed we tried was the Corriedale.  The offspring were more heat tolerant in the summer.  The extra lambs produced with the F+ gene however taxed the milking abilities of the ewes.  The Oxford and Hamp ewes we started with were heavy milking ewes, but this was slowly being diluted in subsequent generations.  We then looked for genetics to improve or maintain milk production in our ewes.  A traditional/production style Dorset was then added to our crossbreeding scheme.  Shortly thereafter, East Friesian/Dorset rams became available as a by-production of the emerging sheep dairy industry in Wisconsin.  We first used an East Friesian/Dorset ram in the fall of 1997.    The results of including the East Friesian and Dorset into our breeding accomplished the goal of improving milk production.  One quarter East Friesian yearling ewes nursed twin lambs without “blinking an eye”.  We had now found the milk to go with the extra lambs from the F+ gene.

All the while we were adding white-faced blood into our flock, we would backcross those ewes to Oxford rams, and later meaty Hampshire rams.  Not all the black-face sired lambs were sent to slaughter; some daughters from carrier ewes were retained for breeding.  This yielded a very mottled flock of ewes.   The breeding scheme became a sort of three way rotational breeding scheme.   We were breeding white-faced ewes to black-faced rams, black-faced ewes to white faced rams with modifications considering lambing ease for ewe lambs.

Recently we acquired a South African Meat Merino (SAMM) ram to include in our cross breeding rotation.  The SAMM ram gave us growth, size and scale, as well as improved wool.  We have used him on our one quarter East Friesian carrier ewes and have been pleased with the results.  This development highlights the flexibility of the F+ gene.  We can incorporate new genetics into our crossbreeding scheme without the need to return to the source of the prolificacy genes.   

The number of lambs weaned is what counts in commercial lamb production; that is what I show in the following table.  The identification of carriers for this table was done with the accumulation of production data over the past ten years, and in a few instances genotyping.  The percent lambs weaned is calculated over the entire flock.  Because we breed our replacement ewe lambs as lambs, I have the percent yearlings lambing listed for each of the years.  The weaning weights are real unadjusted numbers. 

**drought year, some lambs were sold before they were weighed.

You can see that as the percent yearlings increases the weaning percentage drops a bit with it, because yearling ewes have smaller litters. The low weaning average in 2007 was the result of a management error in 2006.  The 2006 drought forced us to wean early, which resulted in mastitis in several ewes that was not discovered until lambing in 2007.  We raised 14 orphans in 2007 and their weights are included in the data set.  (Normally we only have one to three orphans per year.) 

Over the last ten years we have averaged about one third of the flock carrying the F+ gene, replaced not quite one fifth of the flock annually, and weaned on average two seventy pound lambs per ewe.  The primary product that we produce on our farm is feeder lambs.  Our goal is to produce vigorous lambs that have the frame to be fed out to 120-140 pounds.  We sell them in late summer/early fall.  Our feeder lamb buyers have been pleased with the feed lot performance of our lambs. 

Every fall we sell a group of locker lambs directly off pasture.  They are selected from the top of the bell curve distribution of lambs, and are grazed into the fall with our replacement ewe lambs after the feeder lambs have been sold.   The locker lambs are usually harvested in October.

In 2004 the Wisconsin Sheep Breeders Co-op sponsored a carcass contest in conjunction with the Wisconsin sheep and Wool Festival the first weekend after Labor Day in September.  The contest was divided into grass fed and grain fed categories.   Producers were allowed to enter two lambs each, which is what we did.   Because the contest delivery date was September 5, which was a bit early to be harvesting April born lambs off pasture, there was limited participation in the grass fed contest.  There were eight lambs entered in the grass fed category from six different farms, including a Coopworth lamb and a British Suffolk sired lamb from a replicated British three tiered system, breeds recognized as good forage based sheep. Some carcass information of our lambs is listed in the following table.

Both lambs were born and raised as singles, and were our largest lambs at that time.  Our lambs were the two largest grass fed lambs entered in the contest; the next closest lamb in live weight was 110 pounds.  Lamb #54 was grand champion of the grass fed division. It was 38% Dorset, 34% black-faced (primarily Oxford) and 25% East Friesian. It was really the only finished lamb in the grass fed contest.  Lamb #27, was slightly over half black-faced (primarily Hampshire), a quarter Corriedale, the remainder Dorset and East Friesian.  It was a larger framed lamb that should have been fed to a higher weight before being butchered.  Both lambs were 3% or less Booroola Merino and were well suited to fit the needs of the lamb market today. 


The Booroola F+ gene has served our needs well as commercial feeder lamb producers.  We have been able to employ a rotating crossbreeding system to maximize heterosis and the Booroola F+ gene has boosted our weaning percentage to 200%.  Because we did not have to return to the source for our prolificacy genes, we were able to change the breeds employed or try new genetic opportunities such as the SAMM recently.  I believe that our flock productivity is as good as the composite breed system of the Polypay and close to that of an F-1 maternal-terminal crossbreeding system.  The advances in genetic testing have solved the issue of ram selection. 

The twenty years of experience we’ve had with the Booroola F+ gene in our flock demonstrates how effective and simple it is to use if you want to increase your ewe productivity without sacrificing other production traits. We have eliminated the undesirable traits of slow growth and poor muscling of the Booroola Merino, while keeping the prolificacy.   Once the Boroola F+ gene is inserted into a population it can be easily propagated and managed to achieve the desired increase in lamb production.

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