1a. Objectives (from AD-416):
This location will focus on the following objectives over the next five years. Objective 1: Enhance the understanding of control points during the first 24 months of a ewe’s life to improve reproductive efficiency and lifetime production, and develop methods for managing these critical control points to optimize production efficiencies in range sheep flocks. Subobjective 1.A: Quantify relationships among age at puberty of Targhee ewe lambs, ability of Targhee ewes to lamb at 1 year of age, and scrotal circumference of Targhee ram lambs from weaning until approximately 8 months of age, and quantify the response to EBV-based selection strategies on the ability of ewes to lamb at 1 year of age. Subobjective 1.B: Describe the dose-response effects of subacute sodium chlorate exposure on ewe and lamb health and fecal Escherichia coli concentrations, and bactericidal efficacy of chlorate naturally secreted in milk. Objective 2: Evaluate germplasm, selection criteria, and mating systems to improve maternal and paternal genetic lines of sheep to best match western rangeland environments and industry targets for reproductive efficiency, growth, feed/forage efficiencies and meat quality. Subobjective 2.A: Evaluate Polypay, Rambouillet, and 1/4 Romanov × 1/4 White Dorper × 1/2 Rambouillet ewes for lifetime production in a western rangeland, terminal crossbreeding system. Subobjective 2.B: Develop and evaluate a white-faced, composite, paternal genetic line of sheep adapted to extensive rangeland management systems.
1b. Approach (from AD-416):
Market lambs are the primary source of income for United States sheep producers. The mission of the U.S. Sheep Experiment Station is to increase production efficiency of sheep, which includes improving animal well-being, weight of lamb produced during a ewe’s lifetime, lamb growth performance, and carcass merit of lambs. Genetic merit of maternal and paternal lines, reproductive rate, nutrition, health, and management system are some of the factors affecting production efficiency. Our objectives are to 1) enhance the understanding of control points during the first 2 years of a ewe’s life to improve reproductive efficiency and lifetime production, and develop methods for managing these control points to optimize production efficiencies in range-sheep flocks, and 2) evaluate germplasm, selection criteria, and mating systems to improve maternal and paternal genetic lines of sheep to best match western rangeland environments and industry targets for reproductive efficiency, growth, feed/forage efficiencies, and meat quality. The research will focus on 1) determining whether estimated breeding value-based selection strategies can be used to improve the ability of ewes to lamb at 1 year of age, 2) determining whether subacute sodium chlorate exposure will reduce fecal Escherichia coli concentrations and be an effective agent for reducing the incidence of neonatal diarrhea, 3) evaluating maternal genetics for lifetime production in a western rangeland, terminal crossbreeding system, and 4) developing and evaluating a white-faced, composite, paternal genetic line of sheep adapted to extensive rangeland management systems. This research is expected to produce 1) data that can be used to determine the feasibility of actively selecting for the ability of ewes to lamb at 1 year of age (i.e., ewe lamb fertility) and of using scrotal circumference of ram lambs to improve ewe lamb fertility; 2) a sodium chlorate treatment protocol for postpartum ewes and(or) their neonatal lambs that will reduce the incidence of lamb diarrhea and reduce the overall enteropathogenic bacterial load in ewe flocks; 3) data to inform decisions about the genetics of ewe flocks that are suitable for western rangeland, terminal crossbreeding systems; 4) data to inform decisions about crossing paternal genetic lines of rams with maternal genetic lines of ewes to produce terminal-cross market lambs in extensive rangeland production systems; and 5) an alternative terminal-sire genetic line that is suitable for extensive rangeland production systems.
3. Progress Report:
This report documents progress for project 5364-31000-011-00D, which began October 8, 2012. The current project is a continuation, in part, of the former project 5364-31000-010-00D, "Evaluation of Maternal and Paternal Germplasm for Increasing Efficiency of Sheep in Western Rangeland Production Systems", a 5-year progress summary is provided in the annual report for the former project. Progress was made under Objective 1.A. A dataset was constructed using historic Targhee records from the years 1989 to 2011. Relationships among performance measures and lambing percentage at 1 yr-of-age were evaluated. Genetic parameters were estimated and estimated breeding values (EBV) were calculated for traits related to ewe lamb fertility. Sires with more favorable EBV had daughters with higher pregnancy percentages, and subsequent lambing percentages. Matings based on the EBV were made in 2012, and data from the resulting offspring have been used to increase the dataset. Progress was made under Objective 1.B. Assessment of subclinical toxicity of oral chlorate salts in ewes has been completed. Further, efficacy of oral chlorate salt doses on reduction of fecal E. coli was determined. Currently, experiments to determine subclinical toxicity of chlorate salts in neonatal lambs are underway. Progress was made under Objective 2.A. Project lambs were born in spring of 2009, 2010, and 2011. In autumn 2009 to 2012 mature ewes and ewe lambs from each breed type were mated to Suffolk, Columbia, Suffolk × Columbia, or Columbia × Suffolk rams. Progress continues in the collection of production data, and lamb trait data that has been collected at several defined times since the study was initiated. Data from all yearling ewes has been preliminarily analyzed. Progress was made under Objective 2.B. Scientists and collaborators have analyzed a portion of data collected during a 3-year study to characterize Columbia-, MARCIII-, Suffolk-, and Texel-sired F1 lambs for traits of survival, growth, feed efficiency, carcass composition, and meat quality. In 2013, three manuscripts were written. Based on the results in these manuscripts, a new composite terminal-sire line of sheep has been developed. The final composition of the composite sheep was realized in 2010, and, as of 2013, approximately 1537 composite sheep have been produced and are under evaluation for pre-weaning survival and growth, fertility, and ewe production.
1. Early puberty in Targhee ewes. Management systems that enable ewes to lamb at 1 yr of age are thought to be more productive than systems for managing ewes to lamb for the first time as 2-yr-olds. ARS scientists at the U.S. Sheep Experiment Station, Dubois, Idaho, USDA, ARS and Virginia Tech, developed estimated breeding values (EBV) for traits related to ewe lamb fertility. These EBV were used to plan matings of Targhee ewes and rams in 2012. Based on the outcome of the matings, sires with more favorable EBV for ewe lamb fertility had daughters with higher pregnancy percentages, and subsequent lambing percentages. Information from this study will enable sheep producers to select for ewes that lamb at an earlier age and produce more lambs over a lifetime.
2. Safety of chlorate salts in shed-lambing systems. Neonatal diarrhea impairs physical development and early growth potential and ultimately, the lifetime productivity of sheep. ARS scientists at the U.S. Sheep Experiment Station, Dubois, Idaho, Northwest Irrigation and Soils Research Laboratory, Kimberly, Idaho, and Biosciences Research Laboratory, Fargo, North Dakota, are in the final stages of determining the efficacy of chlorate salts to curtail neonatal diarrhea (i.e., scours) in shed-lambing systems. We have established efficacious (reduction in pathogenic E. coli) doses of chlorate salts, identified dosing modes and limitations for chlorate salts, and described chlorate pharmacokinetics in sheep. Reduction in neonatal diarrhea will decrease antibiotic use and related resistance, increase the likelihood that lambs will achieve expected production goals, and result in safer food products for human consumption.
Kirschten, D.P., Notter, D.R., Leeds, T.D., Mousel, M.R., Taylor, J.B., Lewis, G.S. 2013. Evaluation of Columbia, USMARC-Composite, Suffolk, and Texel rams as terminal sires in an extensive rangeland production system: V. Postweaning growth, feed intake, and feed efficiency. Journal of Animal Science. 91(5):2021-2033.