Tamarack Lamb & Wool
Genetic Improvement |
Tamarack Lamb & Wool
The Tamarack Prolific Flock production records are analyzed by Lamb Plan of Australia, where they have processed our performance records from 1996 forward. ( prior to 1996 we used NSIP) Our data set at Lamb Plan includes pedigrees all the way back to 1979 and as of the year 2006 includes over 3436 animals.
Lambs are weighed at 60, 100, and 150 days of age for weaning growth, post weaning growth and carcass evaluation. Weights and carcass measurements are made while lambs are on an all forage diet. Lamb Plan has designed a custom index for Tamarack Lamb & Wool that places emphasis on Mwwt (maternal portion of weaning weight which is an indicator of milking ability) Nlb (numbers of lambs born) and Nlw (numbers of lamb weaned). Secondary emphasis is placed on post weaning gain and loin eye depth while on pasture.
Lamb Plan generates EBV's (Estimated Breeding Values) and (accuracies) for the following traits measured in the Tamarack Flock:
Number of lambs born (Nlb)
Number of lambs weaned (Nlw)
Maternal weaning weight (Mwwt)
Weaning weight (Wwt)
Post weaning weight (Pwwt)
Post weaning loin eye muscle depth (Pemd)
In addition to the above weights, each ewe is assigned a management ease code at lambing. This code is a simple system of +, 0 or - assigned to the ewe's performance in the following areas: milk, mothering, udder, and birth ease within 24 hours of lambing. Any ewe that requires assistance receives a " - " for the trait, a ewe that scraped by without assistance, but could use improvement receives a " 0 " , and ewes demonstrating desirable performance receive a " + " . Milk is simply whether or not she had enough milk to feed the number of lambs born. Mothering is whether she can keep her litter together without requiring tethering or penning. The udder is evaluated for teat shape and placement to assure suckling. Birth ease is how quickly lambs were delivered and whether there is any evidence of difficulty. The objective of this code is to identify ewes with undesirable traits which require additional labor, or could result in the loss of the lamb(s) if assistance is not rendered.
Lambs are pre sorted based on the Tamarack index, emphasizing maternal ebv's. Then the data is examined to look for any outstanding individuals in a single trait that would also be useful. After sorting lambs in the data, they are evaluated physically ( examining teeth, testicles, feet and legs) and the management ease codes are reviewed. Problem animals are culled. The top 1/3 of ewe lambs are retained in the Tamarack flock, while the top 20% of the ram lambs and remaining ewe lambs are offered for sale.
Our printed sales list include ebv's for Mwwt, Nlw, and Pwwt, as well as the maternal index and accuracies.
AFTER the ewes and rams have been selected as keepers by using performance records, THEN they are genotyped for the Booroola B gene. This selection process insures that our Booroola sheep are selected on performance first; not simply because they contain the B gene.
The bar graph below shows the progress our Tamarack flock has made in post weaning weight. The period prior to 2000 represents the unreliability of purchasing US bred "Production Dorset" rams while using adjusted weights to evaluate performance. While these rams were carefully purchased from good producers making an honest effort to select for performance oriented animals, the accuracy of selection based on raw and adjusted data is simply insufficient to produce significant improvement. The one exception in 1992 represents a Dorset AI ram we used from Canada (which represented NZ genetics). That 1992 bar graph clearly demonstrates the importance of EBV selection and further drives home that point.
Significant improvement in growth did not occur until the purchase of several Ile de France rams from the US and Canada. While the North American IDF breeders are not using BLUP* technology, they are purchasing seed stock from European producers which have been using EBVs as a selection tool for many years. Note the boxed in bars from 2003-2006. This represents the improvement made within the Tamarack flock by using home bred Tamarack rams with EBVs.
(*BLUP = Best Linear Unbiased Predictor. An EBV is an example of using BLUP to predict breeding values)
Producers seriously interested in selecting the best we can offer need to select sheep based on their EBVs and not solely on the percentage Ile de France. Within just a few short years after introducing a new purebred IDF ram, our own homebred progeny are outperforming the purebred rams that created them (see boxed in area on chart).
The bar graph below represents progress in maternal weaning weight. Maternal weaning weight has been more difficult to work with as initially the US Dorset genetics showed an antagonism between growth traits and milk production. It took four solid years of selection with EBVs to be able to get both milk and growth moving in the same direction. The period prior to 1996 reflects selection without maternal weaning weight EBVs. The period after 1996 reflects progress made using Lambplan EBVs.
The Chart below shows the importance of selecting rams on EBVs. The two Dorset rams represent rams selected on adjusted weaning and post weaning weights, which are the predominant method of sheep selection in the US. The antagonism between growth and milk is clear in the data of rams selected without EBVs.
The IDF rams represent US and Canadian born IDF rams. "My avg 06" represents the Tamarack flock average for the 2006 lamb crop, and "Top '06 EBVs" represent the EBVs on top individuals within the Tamarack flock.
The chart shows the progress that can be made within the flock by using Tamarack rams selected from the top end of the flock.
The chart below shows the progress we have made in Postweaning loin Eye Muscle Depth (PEMD). This has been done by using ultrasound scanning and rams with loin eye data. A large part of the big 2007 increase was due to the genetic impact of semen we imported from Ireland from the outstanding ram Turnaleary Dollar BT207 H10 owned by Trevor Boyd & Sons of Pomeroy, Northern Ireland.
Summary
Genetic improvement in the Tamarack flock has been the result of using rams with a history of selection using BLUP technology, selecting high indexing rams from within the Tamarack flock, and a means of identifying and culling labor intensive animals from the flock. Genetic improvement continues with the addition of high performing IDF genetics from Ireland selected from the UK Signet performance testing program, and continued use of homebred rams from the top end of each lamb crop. The sum result of has been an actual increase of 20 pounds in 150 day weight and a 20% increase in the number of lambs weaned during the past 8 years. These are numbers producers can take to the bank.
Above AI completed on 97 Tamarack ewes, December 17, 2006, Semen from Turnaleary Dollar BT207 H10
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