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United States Department of Agriculture

Agricultural Research Service

Research Project: EVALUATION OF MATERNAL AND PATERNAL GERMPLASM FOR INCREASING EFFICIENCY OF SHEEP IN WESTERN RANGELAND PRODUCTION SYSTEMS
2010 Annual Report


1a.Objectives (from AD-416)
The overall goal of the U.S. Sheep Experiment Station (USSES) is to increase the production efficiency of sheep. Production efficiency includes weight of lamb produced during a ewe’s lifetime, growth performance of lambs, and carcass quality and merit of market lambs. The following objectives and subobjectives address various elements of production efficiency. Objective 1: Evaluate different breeds and crosses as specialized paternal and maternal lines in an extensive western rangeland, terminal crossbreeding system. Subobjective 1.A: Evaluate different terminal sire breeds for survival, rate and efficiency of growth, carcass composition, and meat quality in extensive western management systems. Subobjective 1.B: Evaluation of Romanov crossbred, Polypay, and Rambouillet ewes as maternal lines in a terminal crossbreeding system. Objective 2: Strategically manipulate management factors to increase the likelihood that a ewe will be productive at 18 mo of age. Subobjective 2.A. Maximize ewe productivity at 18 mo of age through strategic nutrient intervention after weaning. Subobjective 2.B. Strategically use chlorate salts to mitigate neonatal diarrhea in lambs born in a “shed-lambing” system. Subobjective 2.B was developed because neonatal diarrhea reduced weight gain from 50 to 100 d of age; selection based on body weights at 15 or 17 mo of age produced the greatest genetic improvement in body and weaning weights within the flock; and early growth patterns of ewe lambs can affect their reproductive potential later in life. Subobjective 2.C. Validate a stable isotope-ratio method for characterizing the proportion of milk and solid feed in the diet of nursing lambs in range-production settings.


1b.Approach (from AD-416)
The U.S. sheep industry lacks maternal and paternal genetic lines that will enable the industry to adequately address current and future grower, feeder, packer, retailer, and consumer demands. Thus, new research is needed to improve production efficiency of sheep, which includes reproductive efficiency, weight of lamb produced during a ewe’s lifetime, growth performance of lambs, and carcass quality and merit of market lambs..
1)Different breeds and crosses will be evaluated to determine their potential as specialized paternal and maternal genetic lines in an extensive western rangeland, terminal crossbreeding system. Crossbred lambs will be evaluated from birth through harvest to describe sire breeds, define relative optimal market endpoints for the terminal sire breeds evaluated, characterize additive genetic variation for the growth trajectory within breeds, and develop a strategy for producing a composite terminal-sire genetic line of sheep..
2)To quantify ewe productivity, lamb growth, and lamb carcass yield, Polypay, Rambouillet, and Romanov crossbred ewes will be evaluated as maternal genetic lines in a terminal crossbreeding system, using Columbia, Suffolk, Columbia x Suffolk, and Suffolk x Columbia rams. Ewe productivity will be defined as weight of the weaned litter. Carcass yield will be adjusted for body weight at harvest and for carcass backfat thickness..
3)Lifetime productivity of ewes that lamb as yearlings is greater than it is for ewes that lamb later in life. Experiments will be conducted to determine a) whether interval from first detection of a corpus luteum after weaning to breeding affects the likelihood that a ewe will lamb at approximately 12 mo of age; b) whether rate and composition of growth from weaning until conception affects measures of ewe lamb reproduction or the likelihood that a ewe will lamb at approximately 12 mo of age; and c) whether strategic manipulation of management factors, such feeding systems, will increase the likelihood that a ewe will be productive at 18 mo of age..
4)Neonatal diarrhea impairs early growth potential and reduces lifetime productivity of ewes. Experiments will be conducted to determine whether strategic use of chlorate salts will reduce the incidence and severity of neonatal diarrhea in lambs born in a “shed-lambing” system and improve lamb growth performance and lifetime productivity of ewes..
5)Improving lamb growth rate from birth to weaning will improve lifetime productivity of ewes. Procedures, using stable-isotope methods, will be developed to estimate the milk:solid-feed ratio of a lamb’s preweaning diet and better define the variance associated with lamb nutrient intake and growth rates. The results of this research will be used to improve the production efficiency of sheep and improve to ability of the U.S. sheep industry to respond to current and future grower, feeder, packer, retailer, and consumer demands. Formerly 5364-31000-007-00D (10/08).


3.Progress Report
Sheep producers throughout the U.S. claim that fitness traits, including survivability, of terminal-sire breeds of sheep have decreased as mature body size and growth rates have increased, and black fibers in fleeces of terminal-cross market lambs reduce pelt values. U.S. Sheep Experiment Station scientists and their collaborators completed the data-collection phase of a 3-yr study to characterize Columbia-, USMARC Composite-, Suffolk-, and Texel-sired F1 lambs for traits of survival, growth, feed efficiency, carcass composition, and meat quality. Data analyses are in progress, a postdoctoral research associate was hired, and manuscripts will be prepared and submitted to peer-reviewed scientific journals during 2010 and 2011.

Scientists at the U.S. Sheep Experiment Station and the U.S. Meat Animal Research Center are comparing Polypay, Rambouillet, and 1/4 Romanov ewes mated in a terminal-sire crossbreeding system to quantify the lifetime performance of the breed types in extensive management systems. The first lambs in the study were born in the spring of 2009, and in the fall of 2009, ewe lambs from each breed type were mated to Suffolk, Columbia, Suffolk × Columbia, or Columbia × Suffolk rams. Phenotypic data have been collected at several defined times since the study was initiated. This is a long-term study that will take several years to complete.

Slow or difficult births can reduce the survivability of lambs and reduce overall flock production. Scientists at the U.S. Sheep Experiment Station have developed methods for identifying the lamb or lambs within a litter that cause or contribute to dystocia. These methods are being used in a long-term study to determine whether breeding programs can be developed to minimize dystocia and its effects on lamb survival and labor required during lambing.

Three years of a five-year study to better understand factors affecting the likelihood that a ewe will lamb as a yearling was completed in May 2010, and data are being analyzed. Research during the first three years of the study was focused on characterizing ovarian function around the time of puberty. Research for the second 2-year portion of the study was initiated in 2010 to determine whether strategic nutrient intervention will increase the number of ewes that first lamb as yearlings. The data from the project should help us develop management strategies to increase the number of ewes that lamb as yearlings and to increase lifetime productivity of the U.S. ewe flock.

Neonatal diarrhea impairs the growth of young lambs and erodes the overall profitability of sheep enterprises. Scientists at the U.S. Sheep Experiment Station are determining the efficacy of chlorate salt to mitigate neonatal diarrhea. Effective dose rates of chlorate salt have been established that minimized the presence of general Escherichia coli in intestines of ewes and newborn lambs, and the effectiveness of these doses against pathogenic E. coli is currently being determined. Based on the results, an antiscour management strategy will be developed and evaluated in an applied setting using U.S. Sheep Experiment Station flocks in 2011.


4.Accomplishments
1. Terminal-sire breed evaluation: Sheep producers throughout the U.S. claim that fitness traits, specifically survivability, of terminal-sire breeds of sheep have decreased as mature body size and growth rates have increased. In addition, black fibers in fleeces of terminal market lambs reduce pelt values according to pelt processors. U.S. Sheep Experiment Station scientists and collaborators at Virginia Polytechnic Institute and State University, ARS-National Center for Cool and Cold Water Aquaculture, Leetown, WV, ARS-U.S. Meat Animal Research Center, Clay Center, NE, and The Ohio State University are analyzing data from all three years of a study completed in 2009 and conducted to characterize Columbia-, USMARC Composite III-, Suffolk-, and Texel-sired crossbred lambs for traits of survival, growth, feed efficiency, carcass composition, and meat quality. Pelt samples from these lambs will be evaluated at Texas A&M University in 2010. Scientific evaluation of terminal sire breed decline will be made.

2. Evaluation of Maternal Genetics: Scientists at the U.S. Sheep Experiment Station and USDA, ARS, United States Meat Animal Research Center, Clay Center, NE, are comparing Polpay, Rambouillet, and ¼ Romanov ewes mated in a terminal-sire crossbreeding system to quantify the performance of the breed types in extensive management systems. The first lambs in the study were born in the spring of 2009, and in the fall of 2009, ewe lambs from each breed type were mated to Suffolk, Columbia, Suffolk x Columbia, or Columbia x Suffolk rams. Production data (i.e. number of lambs born, number of lambs born alive, number of lambs raised to weaning, birth weight and weaning weight) and individual ewe weights will be collected for the lifetime of the ewes. In addition, a subset of the terminally sired lambs from each ewe breed type will be placed in the feedlot setting until a specified harvest weight to evaluate lamb growth and carcass characteristics. Sheep producers will be able to use data from this long- term study to select the ewe and ram breed types that best fit their breeding program and extensive management practices.

3. Reducing Difficult Births in Sheeps: Slow or difficult births (dystocia) can reduce the survivability of lambs and reduce overall flock production. The use of terminal-sire breeds or genetic lines, which are selected for size, growth potential, and carcass merit, may increase lamb birth weights enough to increase the incidence and severity of dystocia. Scientists at the U.S. Sheep Experiment Station have developed methods for identifying the lamb or lambs within a litter that cause or contribute to dystocia. These methods have been used to initiate a long-term study to quantify dystocia and determine whether breeding programs can be developed to minimize dystocia and its effects on lamb survival and labor required during lambing. Information from this study will be used in sheep production systems to avoid the unintentional selection for dystocia and to reduce, or prevent an increase in, the incidence of dystocia-related morbidity and mortality in ewes and lambs.

4. Eliminating neonatal diarrhea in shed-lambing systems: Neonatal diarrhea or scours, impairs the growth of young lambs and erodes the overall profitability of sheep enterprises. Scientists at the U.S. Sheep Experiment Station are determining the efficacy of chlorate salt to mitigate scours. Effective dose rates of chlorate salt have been established that minimized the presence of general Escherichia coli in intestines of ewes and newborn lambs, and the effectiveness of these doses against pathogenic E. coli is currently being determined. Based on the results, an antiscour management strategy will be developed and evaluated in an applied setting using U.S. Sheep Experiment Station flocks in 2011. This research will result in low-cost, nonantibiotic management solutions for reducing the presence of scour-causing organisms in shed-lambing systems and reduce the overall incidences of scours in lambs

5. Increasing Lifetime Productivity. Lifetime productivity of ewes that first lamb as yearlings is greater than it is for ewes that first lamb later in life. Three years of a five-year study to better understand factors affecting the likelihood that a ewe will lamb as a yearling was completed by ARS scientists in Dubois, Idaho in May 2010. Age to first corpus luteum and first standing heat, indicators of puberty, were established in the USSES Targhee population. From these data, a heritability estimate will be calculated for age to puberty in Targhee sheep. Ultimately, these data are being used to develop breeding and nutrition management programs to increase number of Targhee ewes that lamb as yearlings, and subsequently, overall profitability of U.S. ewe flocks.


Review Publications
Hoesing, L.M., Broughton-Neiswanger, .L., Gouine, K., White, S.N., Mousel, M.R., Lewis, G.S., Marshall, K.L., Knowles Jr, D.P. 2010. Evaluation of a Caprine Arthritis-Encephalitis Virus/Maedi-Visna Virus Indirect Enzyme-Linked Immunosorbent Assay in the Serological Diagnosis of Ovine Progressive Pneumonia Virus in U.S. Sheep. Clinical and Vaccine Immunology. 17(2):307-310.

White, S.N., Mousel, M.R., Reynolds, J.O., Lewis, G.S., Hoesing, L.M. 2009. Common promoter deletion is associated with 3.9-fold differential transcription of ovine CCR5 and reduced proviral level of ovine progressive pneumonia virus. Animal Genetics. 40(5):583-589.

White, S.N., Orourke, K.I., Gidlewski, T.L., Vercauteren, K.C., Mousel, M.R., Phillips, G.E., Spraker, T.R. 2010. Increased risk of chronic wasting disease in Rocky Mountain elk associated with decreased magnesium and increased manganese in brain tissue. Canadian Journal of Veterinary Research. 74:50-53.

Mousel, M.R., White, S.N., Hoesing, L.M. 2010. Association analysis of a CCR5 variant with ewe lifetime production in 3 breeds of sheep. Animal Genetics. 41(2):222-223.

Lekatz, L.A., Caton, J.S., Taylor, J.B., Reynolds, L.P., Redmer, D.A., Vonnahme, K.A. 2010. Maternal selenium supplementation and timing of nutrient restriction in pregnant sheep: Effects on maternal endocrine status and placental characteristics. Journal of Animal Science. 88:955-971.

Lewis, G.S., Gavin, W.G., Goetsch, A.L., Taylor, J.B.,and Thonney, M.L. 2010. Chapter 10: Sheep and Goats, in Guide for Care and Use of Agricultural Animals in Research and Teaching. 3rd ed. Federation of Animal Science Society, Savoy, IL. p. 129-142.

Meyer, A.M., Reed, J.J., Neville, T.L., Taylor, J.B., Hammer, C.J., Reynolds, L.P., Redmer, D.A., Vonnahme, K.A., Caton, J.S. 2010. Effects of nutritional plane and selenium supply during gestation on ewe and neonatal offspring performance, body composition, and serum selenium.. Journal of Animal Science. 88:1786-1800.

Last Modified: 11/24/2014
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