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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
2011 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
This research supports the 2007-2012 Food Animal Production National Program (NP 101) Action Plan, Component 1 (Understanding, Improving, and Effectively Using Animal Genetic and Genomic Resources), Problem Statements 1C and 1D; and Component 2 (Enhancing Animal Adaptation, Well-Being and Efficiency in Diverse Production Systems), Problem Statements 2B and 2C.

ARS research scientists at the U.S. Sheep Experiment Station (USSES)in Dubois, ID and their collaborator at Virginia Tech have analyzed data from a 3-year study to characterize Columbia-, USMARC Composite-, Suffolk-, and Texel-sired F1 lambs for several critical production traits. Three manuscripts have been written and will be submitted to peer-reviewed scientific journals in FY 2011. Data from this study were used to initiate the development of a new composite terminal-sire genetic line of sheep. The initial breed crosses, with the planned proportion of each of the three founding breeds, were realized in 2010, and, as of 2011, approximately 300 of the sheep have been produced and are under evaluation.

Studies to determine the efficacy of chlorate salt for reducing the incidence and severity of neonatal diarrhea in lambs were completed. Dose rates of chlorate salt for reducing intestinal Escherichia coli, which are usually associated with neonatal diarrhea, were published in 2011. In 2011, we used the efficacious dose rates of chlorate salt to develop and evaluate a nonantibiotic, antidiarrhea strategy; the data are now being analyzed.

Lifetime productivity of ewes that lamb as yearlings is greater than that of ewes that lamb for the first time as 2-year olds. Year 5 of a 5-year study to better understand factors affecting the likelihood that a ewe will lamb as a yearling was completed in May 2011. The data are being currently analyzed.

Slow or difficult births can reduce the survivability of lambs and reduce overall flock production. Thus, USSES scientists developed methods for identifying the lamb or lambs within a litter that cause or contribute to dystocia. This is a long-term study, which was initiated in 2006, to determine whether breeding programs can be developed to minimize dystocia and its effects on lamb survival. Additional data were collected in 2011. Data from 2006, 2007, and 2008 were used for a manuscript that will be submitted to a peer-reviewed scientific journal in FY 2011.

Scientists at the USSES are comparing Polypay, Rambouillet, and 1/4 Romanov ewes mated in a terminal-sire crossbreeding system to quantify the lifetime performance of these breed types. Lambs for this study were born in spring of 2009, 2010, and 2011. In autumn 2009 and 2010, ewe lambs from each breed type were mated to Suffolk, Columbia, Suffolk × Columbia, or Columbia × Suffolk rams. This same breeding plan will be followed in the autumn of 2011. Production data (e.g., ewe and lamb body weights, number of lambs born, number of lambs weaned, and ewe wool quality) 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.


4.Accomplishments
1. Terminal-sire breed evaluation—Postweaning growth and body composition. The lack of current information about the relative merits of various breeds of sheep limits the ability of U.S. sheep producers to select sire breeds that match specific production environments and improve the value of market lambs. To address this issue, ARS research scientists at the U.S. Sheep Experiment Station in Dubois, ID, and their collaborators at Virginia Tech, ARS-National Center for Cool and Cold Water Aquaculture, Leetown, WV, and ARS-U.S. Meat Animal Research Center, Clay Center, NE, determined whether breed of sire affected postweaning growth and body composition of crossbred lambs. Columbia, USMARC-Composite, Suffolk, and Texel rams, which are terminal-sire breeds used to sire high-value market lambs, were mated with Rambouillet ewes, which have superior maternal abilities, to produce crossbred lambs. The results of this research indicate that Suffolk-sired lambs were equal or superior to lambs sired by the other three breeds in postweaning growth, leanness, and loin muscle area at comparable ages; leanness at 60 kg of body weight; and loin muscle area at a backfat depth of 9.1 mm, which is the boundary between U.S. Yield Grades 3 and 4; but inferior in loin muscle area to Texel- and Composite-sired lambs at comparable body weights. Sheep producers can use this information to select, among the breeds evaluated, the sire breed with the greatest ability to improve the value of their market lambs.

2. Terminal-sire breed evaluation—feedlot returns. The U.S. sheep industry needs objective estimates of feedlot return from the offspring of terminal-sire breeds of sheep in order to improve the profitability of market lamb production, but terminal-sire breed-comparison data for breeds of sheep in the U.S. are lacking. Thus, ARS research scientists at the U.S. Sheep Experiment Station in Dubois, ID, and their collaborators at Virginia Tech and the ARS-National Center for Cool and Cold Water Aquaculture, Leetown, WV, determined whether breed of sire affected feedlot returns, which were calculated from current lamb prices, feed costs, and other typical costs, of crossbred market lambs. Columbia, USMARC-Composite, Suffolk, and Texel rams, which are terminal-sire breeds used to sire high-value market lambs, were mated with Rambouillet ewes, which have superior maternal abilities. Feedlot returns were greater for Suffolk-sired than for Columbia- and Texel-sired lambs, and intermediate for Composite-sired lambs. Feedlot returns were more closely associated with body weight gain and feed efficiency (i.e., body weight gain per unit of feed consumed) than with any of the other traits measured. Based on the results of this study, U.S. sheep producers can use large, fast-growing, terminal-sire breeds, with increased genetic merit for postweaning body weight gain, and simultaneously improve monetary returns from producing feedlot lambs.

3. Terminal-sire breed evaluation—lamb survival. Sheep producers throughout the U.S. claim that fitness traits, specifically survivability, of lambs have decreased as mature body size and growth rates have increased during the last 20 to 30 years. To address this issue, ARS research scientists at the U.S. Sheep Experiment Station in Dubois, ID, and their collaborators at Virginia Tech, ARS-National Center for Cool and Cold Water Aquaculture, Leetown, WV, and ARS-U.S. Meat Animal Research Center, Clay Center, NE, determined whether breed of sire affected the survival of crossbred lambs from birth to market age. Columbia, USMARC-Composite, Suffolk, and Texel rams, which are terminal-sire breeds used to sire high-value market lambs, were mated with Rambouillet ewes, which have superior maternal abilities, and the traits of birth weight, survival, growth, feed efficiency, carcass composition, and meat quality of the crossbred lambs were evaluated. Breed of sire did not affect the survival of crossbred lambs, but breed of sire affected the other traits that were measured. Based on this information from this research, sheep producers can use any of the sire breeds that were evaluated to produce high-value market lambs, without reducing lamb survival from birth to market age.

4. Terminal-sire breed evaluation—association between birth weight and lamb survival. The lack of information about factors that influence lamb survival from birth to weaning limits the ability of U.S. sheep producers to identify lambs at risk and develop management strategies to reduce the incidence of lamb mortality. To address this issue, ARS research scientists at the U.S. Sheep Experiment Station in Dubois, ID, and their collaborators at Virginia Tech, ARS-National Center for Cool and Cold Water Aquaculture, Leetown, WV, and ARS-U.S. Meat Animal Research Center, Clay Center, NE, determined whether lamb birth weight affected the probability of a lamb dying before it was weaned at approximately 132 days of age. Columbia, USMARC-Composite, Suffolk, and Texel rams, which are terminal-sire breeds used to produce high-value market lambs, were mated with Rambouillet ewes, which have superior maternal abilities, to produce crossbred lambs for this study. The interaction between sire breed and birth weight affected lamb survival from birth to weaning and revealed that light birth weight (i.e., less than average for the individual sire breed x Rambouillet ewe cross) Columbia- and Suffolk-sired lambs had a greater risk of dying than did lightweight Composite- and Texel-sired lambs. However, the risk of death of did not increase substantially for heavyweight lambs from any of the sire breed x Rambouillet ewe crosses. Producers can use lamb birth weights to identify lambs with greater probabilities of dying before weaning and then implement management plans to reduce death losses.

5. Terminal-sire breed evaluation—feed intake and efficiency of growth. The U.S. sheep industry needs objective estimates of feed efficiency (i.e., body weight gain per unit of feed consumed) for the offspring of terminal-sire breeds of sheep to improve market lamb production, but terminal-sire breed-comparison data for modern breeds of sheep in the U.S. are lacking. Thus, ARS research scientists at the U.S. Sheep Experiment Station in Dubois, ID, and their collaborators at Virginia Tech, ARS-National Center for Cool and Cold Water Aquaculture, Leetown, WV, and ARS-U.S. Meat Animal Research Center, Clay Center, NE, determined whether breed of sire affected feed intake and efficiency of growth of crossbred market lambs. Columbia, USMARC-Composite, Suffolk, and Texel rams, which are terminal-sire breeds used to sire high-value market lambs, were mated with Rambouillet ewes, which have superior maternal abilities, and feed intake and efficiency of growth of the crossbred lambs were evaluated. Suffolk-sired lambs consumed more feed, but they gained more body weight and gained more weight per unit of feed consumed, than did Columbia-, Composite-, and Texel-sired lambs. The U.S. sheep industry can use data from this study to select modern terminal-sire breeds that will promote their production objectives for growth and efficiency of market lambs, which, depending on production system, may or may not favor the largest, fastest growing lambs.

6. 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. ARS research scientists at the U.S. Sheep Experiment Station in Dubois, ID, established effective dose rates of chlorate salt that minimized the presence of generic Escherichia coli in intestines of ewes and newborn lambs, and the effectiveness of these doses against pathogenic E. coli in neonatal lambs. Based on the results, an antiscour management strategy was developed and evaluated in an applied setting using U.S. Sheep Experiment Station flocks in 2011. These results are being used to create 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. After being thoroughly evaluated for efficacy, these management solutions will be transferred to U.S. sheep producers to enable them to reduce the incidence of neonatal scours and the subsequent morbidity and mortality.

7. 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. ARS research scientists at the U.S. Sheep Experiment Station in Dubois, ID, established the age to first corpus luteum and first standing heat, indicators of puberty, in the USSES Targhee population. From these data, heritability estimates are being calculated for age to puberty in Targhee sheep. 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.

8. Evaluation of maternal genetics. Maternal genetics contributes to overall profitability of sheep enterprises. ARS research scientists at the U.S. Sheep Experiment Station in Dubois, ID, and USDA, ARS, U.S. Meat Animal Research Center, Clay Center, NE, are comparing Polypay, 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 second set of lambs in the study were born in the spring of 2010, and in the fall of 2010, 2 year old ewes and 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, wool characteristics) and individual ewe weights will be collected for the lifetime of the ewes. 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 production goals and extensive management practices.


Review Publications
Smith, D.J., Taylor, J.B. 2011. Chlorate analysis in matrices of animal origin. Journal of Agricultural and Food Chemistry. 59:1598-1606.

Broughton-Neiswanger, L.E., White, S.N., Knowles Jr, D.P., Mousel, M.R., Lewis, G.S., Herndon, D.R., Hoesing, L.M. 2010. Non-maternal transmission is the major mode of ovine lentivirus transmission in a ewe flock: A molecular epidemiology study. Infection, Genetics and Evolution. 10(7):998-1007.

Taylor, J.B., Dungan, R.S., Lewis, G.S. 2011. Sodium chlorate reduces presence of Escherichia coli in feces of lambs and ewes managed in shed-lambing systems. Journal of Animal Science. 90:381-386.

Meyer, A.M., Reed, J.J., Neville, T.L., Maddock-Carlin, K.R., Thorson, K.A., Taylor, J.B., Reynold, L.P., Luther, J.D., Redman, J.S., Vonnahme, K.A., Caton, J.S. 2011. Nutritional plane and selenium supply during gestation impact yield and nutrient composition of colostrum and milk in primiparous ewes. Journal of Animal Science. 89:1627-1639.

Thelen, T.M., Taylor, J.B., Mayland, H.F. 2008. Effects of including alfalfa hays that were harvested in the morning or evening in diets of newly-received sheep. Professional Animal Scientist. 24:473-478.

Neville, T.L., Caton, J.S., Hammer, C.J., Reed, J.J., Luther, J.S., Taylor, J.B., Vonnahme, K.A. 2010. Ovine offspring growth and diet digestibility are influenced by maternal Se supplementation and nutritional intake level during pregnancy despite a common postnatal diet. Journal of Animal Science. 88:3645-3656.

Lekatz, L.A., Caton, J.S., Taylor, J.B., Reynolds, L.P., Redmer, D.A., Vonnahme, K.A. 2011. Maternal selenium supplementation and timing of nutrient restriction in pregnant sheep: Impacts on nutrient availability to the fetus. Journal of Animal Science. 89:59-76.

Last Modified: 11/23/2014
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