Tca_national sheep improvement.cdr

National sheep improvement program in the USA: with emphasis
on hair sheep evaluations
Paper presented at 3 SINCORTE, Joao Pessoa, Paraiba, Brazil, November 2007 (published with the approval of the Coordination of 3 SINCORTE)2 PhD, President of the NSIP Board of Directors Abstract - After 40 years of use in the livestock industry, the major technology for identifying superior performance in sheep
breeding stock is still BLUP (Best Linear Unbiased Prediction) and its use to produce EPDs. For 20 years, the National
Sheep Improvement Program has provided EPDs for the USA sheep industry. Flocks involved in NSIP have experienced
consistent improvement in performance. Sheep scientists predict that in ten to fifteen years, there will be the development of
several new DNA tests that will improve a sheep seedstock producer's ability to identify superior sheep. Presently two traits
that increase percentage of carcass muscling are available. These are the Myostatin and Carwell DNA tests. The industry
needs to be ready to adopt new tests that identify commercially important traits as they come online. Future work for NSIP
needs to include a) development of terminal sire indices that include lamb survival, b) development of selection indices that
include both specific DNA tests and EPDs and c) development of more selection indices that directly link genetic traits to
economic return.
Keywords: performance, DNA tests, carcass muscling, selection indice, genetic traits Programa nacional de melhoramento de ovinos nos EUA: com ênfase
sobre avaliações de ovinos
Resumo - Após 40 anos de uso na pecuária, a melhor tecnologia para a identificação de um desempenho superior em
reprodutores ovinos ainda é BLUP (melhor predição linear não viciada) e seu uso para a produção de DEPs. Há 20 anos, o
Instituto Nacional do Programa de Aperfeiçoamento Ovinos forneceu DEPs para a indúsria de caprinos do EUA. Rebanhos
envolvidos em NSIPE experimentaram uma melhoria consistente de desempenho. Cientistas de ovinos prevêem que, em
dez a quinze anos, haverá o desenvolvimento de vários novos testes de DNA que irá melhorar a capacidade do produtor para
identificar ovinos superior. Atualmente, duas características que aumenta o percentual da musculatura de carcaça estão
disponíveis. Estes são os testes de miostatina e Carwell DNA. A indústria precisa estar preparada para adoptar novos testes
que identificam características comercialmente importantes como eles vêm em online. O trabalho futuro para NSIP deve
incluir a) desenvolvimento de índices de reprodutor terminal, que incluem a sobrevivência dos cordeiros, b)
desenvolvimento de índices de seleção que incluem testes de DNA específicos e DEPs e c) desenvolvimento de mais índices
de seleção que ligam diretamente características genéticas para retorno econômico.
Palavras-chave: desempenho, teste de DNA, musculatura de carcaça, índice de seleção, características genéticas Introduction
Observed performance includes both genetic and environmental components. To effectively and accurately The U.S. National Sheep Improvement Program (NSIP) identify superior genetics requires that seed stock producers was developed to provide the US sheep industry with use technology that separates the environmental and genetic modern genetic evaluation techniques starting in 1986. components of observed performance (nature versus These techniques lead to much more rapid genetic change nurture). The second is to create selection indices that than was previously possible. In the USA, very effective use balance optimal performance and economics of production of Best Linear Unbiased Prediction (BLUP) and the with carcasses and product that packers and consumers want. expected progeny differences (EPDs) produced has resulted The best way to separate genetic and environmental in large increases in milk and meat production in the dairy, components of performance is the use BLUP to provide beef and swine industries. The use of use of NSIP and EPDs by the USA sheep industry has not been as wide spread. This work will consist of four parts: a) the traits evaluated Though, acceptance by the industry has been increasing by NSIP for the sheep industry, b) breeds and species enrolled in NSIP, c) recent traits developed for NSIP and d) There are two distinct difficulties in selecting superior examples of breed progress. The NSIP technologies can be breeding stock. The first is that the observed phenotypes of used to access genetic improvement across the whole range all important performance traits are only partially heritable. of economically important production traits. NSIP currently Tecnol. & Ciên. Agropec., João Pessoa, v.4, n.4, p.33-39, dez. 2010
provides expected progeny differences (EPDs) for weaning Table 2. Breeds & Species Evaluated in NSIP 2007.
and post-weaning weights, litter size at birth, maternal ability and for wool sheep, several measures of fleece Table 1. Major traits evaluated for NSIP sheep data
New Breeds/Species to be added in 2008
mostly single trait selection for maximized post-weaning growth. With less use of EPDs in the USA sheep industry, Ewe Productivity Index – lbs lamb weaned/ewe/yr single trait selection for extreme growth has not created the same problem as in the beef industry. However, unbalanced selection in sheep breeds in the show ring has created breeds with problems with significant issues with reproductive efficiency. Sheep seed stock primarily selected for frame and height and visual evaluation do not result in sheep superior for meat production and lamb survival. If the Programs for genetic evaluation of livestock such as calf/lamb is not born, it does not matter how fast they grow. NSIP provide a set of tools and procedures for prediction of Even over selection for muscling often results in less lamb genetic merit based on objective measurements of animal vigor and less pounds of marketed lamb.
performance. The main genetic evaluation tool returned to Preliminary work at the United States Department of the breeder is the EPD. EPDs evaluate relative performance Agriculture Meat Animal Research Center (USDA-MARC) of animals raised in different flocks and different years. By in Nebraska found an inverse relationship between rate of evaluating “relative performance” and the use of advanced growth and lamb survival (personal communication, Dr mathematical and statistical analyses, EPDs accurately Kreg Leymaster). In this preliminary study, lambs sired by determine the relative genetic merit of animals. Across flock breeds with fast growth had lower lamb survival than slow EPDs helps breeders factor out the environmental growing breeds survival. In the cross-bred production differences including but not limited to nutrition, number system at USDA-MARC, fast-growing terminal sires produced no more pounds of lamb at market because of EPDs are the most accurate estimate of genetic merit decreased lamb survival to market age.
available to livestock producers and are one set of tools The answer is balanced selection. Seed stock producers available to breeders to select superior sheep. They need to need to prioritize lamb survival and vigor, no matter whether balanced and optimized for the production and management their breed is a terminal sire or maternal breed. Unborn lambs systems in use and balanced with other traits including or lambs that die before marketing (low birth rate and lamb structural soundness, shedding and muscling.
survival) do not bring profit to the producers no matter how Participation in the National Sheep Improvement superior their genetics for growth and muscling are. Program requires that breeders accurately record weights, Most selection indices for maternal breeds include number born, sire and dam identity. Most progressive percent weaned and need to be extended to terminal sire breeders are already recording this information. These breeds as well. There are many of these indices around. Drs records and weights are submitted to the NSIP Genetic Vanimisetti, Notter and Kuehn at Virginia Technological Evaluation Center along with records from other breeders University and the NSIP Genetic Evaluation Center recently from the same breed. NSIP returns EPDs to the breeders that created a new Ewe Productivity Trait EPD (index) for they can then use to retain and purchase superior stock.
Katahdin Hair Sheep. The development of the NSIP Ewe Currently thirteen breeds are contracted with the National Productivity Index has minimized calculation errors Sheep Improvement for genetic evaluations. The current inherent in most indices provided to producers around the major breeds are Suffolk, Targhee, Polypay and Katahdin. A world. In future years, more breeds will be able to use the recent addition is the Boer Goat. Breeds & Species evaluated The Katahdin breed, a shedding hair sheep developed in In the USA, EPDs have been used to maximize milk the USA is widely viewed as a moderately prolific easy care production in dairy cattle and growth in beef cattle. ewe by the USA sheep industry. The first Katahdin flock Maximization growth and milk production has resulted in submitted data to NSIP in 1996. Katahdin EPDs exhibit an cattle that do not breed back and are open. In beef cattle, there increase in performance, with the exception of percent lamb is a high frequency of dystocia caused by unbalanced and Tecnol. & Ciên. Agropec., João Pessoa, v
60-Day Weaning Weight, lbs
Maternal Milk, lbs
Milk plus Growth EPD, lbs
120-Day Postweaning Weight, lbs
Percent Lamb Crop, lambs born per 100 ewes
Number weaned, lambs per 100 ewes
Pounds weaned, lbs
Number of lambs born in each year
No. of lambs born
Figure 1. Genetic trends in NSIP Polypay flocks.
Tecnol. & Ciên. Agropec., João Pessoa, v.4, n.4, p.33-39, dez. 2010
From the data of over 7500 litters, mature Katahdin ewes have a 2.1 lambs/ewe lambing. Katahdin NSIP breeders have 60-Day Weaning Weight, lb
not selected for increased prolificacy. Definitive improvements in genetic performance are being made. Flocks involved in NSIP have experienced consistent improvement in performance, Polypay (Figure 2) and 60-d Weaning Weight, lbs
120-Day Postweaning Weight, lb
60-d Maternal Milk, lbs
Maternal Milk, lb
120-d Postweaning Weight, lbs
Percent Lamb Crop, lambs/100 ewes
Percent Lamb Crop
Figure 2. Genetic trends in NSIP Polypay flocks.
Figure 3. Genetic trends in NSIP Suffolk flocks.
Tecnol. & Ciên. Agropec., João Pessoa, v
Ewe productivity EPDs are predicted from ewe data for litter size, number weaned, and average pounds weaned utilizing the genetic correlations amongst litter size, number weaned, average pounds weaned, and total pounds weaned traits. The component traits are heritable (Table 3) and intercorrelated (Table 4). Pounds weaned/ewe lambing is most highly correlated with percent weaned indicating that reproductive efficiency is a key economic trait. Fecal egg count
Table 3. Heritability estimates for Katahdin ewe
Sire 1 Sire2 Sire 3
Sire 4 Sire 1 Sire 2 Sire 3
a Ewe productivity measured as total pounds weaned per ewe lambing Fecal egg count, epg
Table 4. Genetic correlations among ewe productivity and
Figure 4. Comparisons of progeny fecal egg counts at
8weeks (early-life) and 22 weeks (late season) for sires evaluated in each year in flock 1 (upper panel) and flock 2 a Ewe productivity measured as total pounds weaned per ewe lambing lambs born), percentage of lambs weaned, lamb weight, Katahdin NSIP breeders now have the tools to select for fertility and ewe viability. Optimal performance levels of the increased growth and milk. The trend lines indicate that Ewe Productivity Trait reflect a genetic balance in harmony progress is being made at improving performance (see with production environment and management conditions.” Figure 4). Many livestock breeds and species have used In the Katahdin, there is substantial range in expression of growth EPDs to rapidly increase growth, but the need for kilograms lamb weaned and thus the ability to greatly more emphasis on maternal behavior, lamb vitality and increase production. Within the Katahdin sire summary for survival from birth to market are key.
the first year of evaluation, a 38% difference in the Percent Charles Parker (retired Director of the U.S. Sheep Weaned EPD. The top ram had average prolificacy but had Experiment Station in Dubois, Idaho) has written, “At this daughters that were weaning 18% above the breed average. transitional stage of the U.S. sheep industry, there is no more Looking at a sample of animals for the Ewe Productivity important economic trait to the commercial sheep industry Index, a full range of patterns of EPDs for Percent Lamb than – kilograms of quality lamb marketed per ewe per year. Crop, Percent Weaned and Pounds Lamb Weaned/Ewe are Development of the NSIP - Ewe Productivity Trait based on observed. One can select for animals that have the pounds of lamb weaned is a major technological contribution prolificacy needed for your management system and still for genetically improving meat production and profitability wean high percentages of lambs. Animals with genetic of sheep. Litter weight per ewe at weaning is a biological tendency to wean low percentages can be selected against. index strongly affected by related reproductive and maternal Ram # 1 is an excellent animal in terms of reproductive attributes. Research studies at the U.S. Sheep Experiment efficiency and maternal performance. Daughters of Rams 2 Station, Dubois, ID, have shown that selecting for litter and 3 are predicted to lose a fair percentage of their lambs. weight is associated and improves prolificacy (number of This trait strongly predicts profitable production (Table 5).
Tecnol. & Ciên. Agropec., João Pessoa, v.4, n.4, p.33-39, dez. 2010
Table 5. Sample animals with a range of ewe productivity
Katahdin sheep for parasite resistance (Notter et al., 2007). It is worth mentioning the development of this particular EPD since it high lights that some sheep are resistant to parasites at 60 Day Milk
Kgs weaned/
% Lamb Crop % Weaned
a much earlier age than previously believed and that it is a + Growth EPD
ewe lambing
highly heritable trait. In the Katahdin, a composite breed of shedding sheep with both Caribbean hair and English wool breed ancestry, heritability of parasite resistance is estimated at 50% and is expressed at 8 weeks of age. Most estimates for heritability of parasite resistance suggest 20-30% and not earlier than 17-20 weeks of age. This is consistent with studies that find that hair sheep breeds from the Caribbean Gastrointestinal nematodes affect profit and production. are more resistant to parasites (Vanimisetti et al., 2004b). It is For over 40 years, small ruminant producers managed the important that sheep producing countries include sheep problem with the use of anthelmintics. In recent years, the genetics from the tropics that have early development of prevalence of nematodes resistant to anthelmintics is increasingly common. Sue Howell and Ray Kaplan of the Seed stock producers in the major sheep producing University of Georgia Veterinary Medical School recently countries of the world use many indices to meet breeding quantified the amount of anthelmintic resistance in flocks objectives. Many of these include financially important and herds in the Southeastern United States, a region with hot traits, but few weight the component traits for production and humid summer temperatures. Farms with goats, which costs and market returns. To optimize selection for financial are typically more susceptible to nematodes, have greater return and production, seed stock producers need indices that amounts of anthelmintic resistance. To be classified as an weight the economic costs and market value. Recently, the operation with resistant worms, 10% or more of the worms National Sheep Improvement Program in conjunction with do not respond to the anthelmintic. This does not mean that researchers at Virginia Polytechnic Institute and State 94% of the sheep farms in the Southeastern USA can not use University and Montana State University released a new the benzimidazoles, it means that 94% of the flocks have breeding objective for Targhee sheep (Borg et al., 2007). worms with detectable resistance and need to be cautious in Targhees are a medium/fine wool breed general purpose breed often used in extensive range conditions of the western Most of the major sheep producing countries are developing or have developed EPDs for identifying parasite Borg and coworkers produced an aggregate breeding resistant sheep. In certain sheep producing regions, where value predicted directly from a published multi-trait EPD by climatic conditions are very favorable for parasites weighting each EPD by its economic value. Weightings were anthelmintic resistance is common. The extent of the determined by using a bio-economic model that predicted problem can be severe. In the southeastern USA, a majority changes in animal performance, feed requirements, costs and of the sheep flocks have barber pole worms, Haemonchus returns associated with changes in each EPD. Feed costs for contortus, with resistance to the available anthelmintics ewes and lambs were predicted to be greater with selection for increased weaning weight, maternal milk, fleece weight and percent lamb crop. The majority of these flocks sell Table 6. Haemonchus contortus (Barber Pole worm)
lambs as feeders. Lambs with high weaning weights are resistance to three classes of anthelmintics in sheep and goat discounted by the lamb buyers. Thus, the model had to operations in the SE USA, Virgin Islands and Puerto Rico include economic losses for lambs discounted for being too using the DrenchRite® larval development assay.
Borg's results are summarized in Figure 5. Each bar in the % with benzimidazole % with levamisole % with ivermectin graph indicates the change in value from one generation to the next by holding all traits constant but one. The trait of interest is moved one standard deviation greater between the two generations. Values greater than 100% for a trait indicate Personal communication, Sue Howell & Ray Kaplan, University of an increase in return by increasing that trait. Values below 100% indicated decreased return for increased selection for that trait. The greatest economic return for these Targhee range flocks is created by increasing the percent lamb crop. Because of the widespread resistance to anthelmintics in The amount of increased economic return varies based on many sheep production areas, the importance of selecting for cost of feed. Significant increase in value of marketed lambs parasite resistant breeding stock will become increasingly is also realized by selecting on weaning weight. Note that important in the 21 century. Recently the National Sheep increased ewe size (yearling weight) decrease economic Improvement Program in the USA developed a new EPD for Tecnol. & Ciên. Agropec., João Pessoa, v
DNA tests and EPDs and c) development of more selection indices that directly link genetic traits to economic return.
The author thanks David Notter and his Research Lab Consisting of Larry Kuehn, Bindu Vanimisetti and Randy Relative Returns (%)
Borg of the National Sheep Improvement Program Genetic Evaluation Center at Virginia Polytechnic Institute and State University for their expertise, analysis and contributions to Selection Criteria
Figure 5. Returns over feed costs across generations 1 and 2 associated
with different selection criteria with high or low feed costs. Values are
Borg, RC, DR Notter, LA Kuehn, and RW Kott. 2007. expressed as a percentage of returns over feed costs in the base flock.
Breeding Objectives for Targhee Sheep. J. Anim. Sci. WW = weaning wt, MM = maternal milk, YW = yearling wt, FW = fleece <>.
wt, FD = fiber diameter, SL = staple length, PLC = percent lamb crop. Notter, DR, JLM Morgan, HB Vanimisetti. 2007. The National Sheep Industry Improvement Program Releases a Concluding Remarks
New Tool for Genetic Improvement of Parasite Resistance: Development of a Fecal Egg Count EPD for Katahdin Sheep. 1. Flocks involved in NSIP have experienced consistent improvement in performance. 2. Sheep scientists predict that in ten to fifteen years, there Vanimisetti, HB, DR Notter, and LA Kuehn. 2004a. Genetic will be the development of several new DNA tests that will Evaluation of Ewe Productivity in Katahdin Sheep. improve a sheep seedstock producer's ability to identify Katahdin NSIP Notebook, No. 5, National Sheep 3. Presently two traits that increase percentage of carcass muscling are available. These are the Myostatin and Carwell Vanimisetti, HB, SP Greiner, AM Zajac, DR Notter. 2004b. Performance of hair sheep composite breeds: Resistance of 4. The industry needs to be ready to adopt new tests that lambs to Haemonchus contortus. J. Anim. Sci. 82:595-604.
identify commercially important traits as they come online. 5. Future work for NSIP needs to include a) development of Vanimisetti, HB, DR Notter, LA Kuehn. 2007. Genetic terminal sire indices that include lamb survival, b) (co)variance components for ewe productivity traits in development of selection indices that include both specific Katahdin sheep. J. Anim. Sci. 85:60–68.
Tecnol. & Ciên. Agropec., João Pessoa, v.4, n.4, p.33-39, dez. 2010


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