Location: Range Sheep Production Efficiency Research
2023 Annual Report
Objectives
To remain globally competitive, the U.S. sheep industry must increase the volume and quality of marketable products. Yet, domestically, U.S. sheep producers must also achieve ecologically positive production systems to remain viable. Although consumer demand for U.S. sheep meat and wool products is robust, changing societal demands for public rangeland use, lagging acceptance of genetic tools, and production inefficiencies hamper the ability of the U.S. sheep industry to generate quality meat and wool at viable profit margins. Fashioning integrated sheep genetic resources to enhance rangeland ecological functions, creating national sheep reference flocks, developing solutions to increase lamb survivability, and extending ewe longevity would foster robustness and competitiveness of the U.S. sheep industry and the sustainability of rural livelihoods. To this end, our aim is to develop ecologically oriented sheep genetic resources and production tools to increase lifetime production efficiency and ecological utility of sheep originating from rangeland production systems. Our approach involves integrated efforts with universities and other Agricultural Research Service units to advance the discovery of unique traits and genetic markers associated with herbivory preferences of grazing sheep, facilitate robust genetic x environment x management evaluations and discovery of novel production efficiency traits, and develop solutions to mitigate anti-productive effects of sheep diseases and reduce the sheep industry’s use of antibiotics. Accordingly, the project plan objectives and subobjectives are:
Objective 1: Develop ecologically-oriented sheep genetic resources applicable towards increasing lifetime production efficiency and grazing utility of sheep originating from extensive rangeland systems.
Subobjective 1.A: In sheep, quantify the association between taste sensitivity towards bitter flavor and herbivory of browse species.
Subobjective 1.B: In sheep, identify genetic markers/candidate genes that are associated with taste sensitivity towards bitter flavor.
Objective 2: Develop non-antibiotic solutions for increasing sheep longevity in the production system.
Subobjective 2.A: Determine the utility of chlorate salts to mitigate anti-productive effects of sub-clinical mastitis in early and near-peak lactation ewes on annual weight of lamb weaned.
Accomplishment of these objectives will result in sheep genetic resources applicable for enhancing and conserving ecosystems, solutions for increasing ewe production efficiency, and non-antibiotic alternatives to increase ewe longevity and lamb survival. Stakeholders include those focused on meat and wool production and marketing, genetic flock resources, land management, habitat and wildlife conservation, and targeted grazing.
Approach
For Objective 1, we will develop of series of tests to identify sheep with low to high taste sensitivity towards bittering compounds placed in the feed, determine the herbivory preferences of sheep based on sensitivity towards bitter flavor, and further validate use of genetic markers to identify sheep with specific taste sensitivities and herbivory preferences. Experimental goals specific to Objective 1 are: 1) Develop a feed-based, bitter-taste sensitivity classification method that generates precise classification results in agreement with Hensley et al. (2019); 2) Develop a high-throughput, feed-based, bitter-taste sensitivity classification method where multiple sheep in group-fed environments can be simultaneously classified; 3) Determine if bitter-taste sensitivity can be used as an accurate predictor of sheep herbivory of shrubs in an actual grazing application; and 4) Identify genetic markers/candidate genes that are useful for identifying and predicting herbivory of sheep.
For Objective 2, we will extend previous efforts in evaluating the effect of adding sodium chlorate to the drinking water of periparturient ewes to reduce diseases associated with pathogenic Enterobacteria. The experimental hypothesis (alternative) specific to Objective 2 is: Ewe consumption of sodium chlorate (via drinking water) at early and near-peak lactation reduces occurrence of Escherichia coli-induced subclinical mastitis in sheep and, thus, mitigates anti-productive effects of mastitis. Specific focus will be placed on evaluating performance and productivity of ewes and lambs from an environment where measures are taken to reduce the likelihood of disease.
Progress Report
In support of Objective 1, research was initiated on developing ecologically-oriented sheep genetic resources applicable towards increasing lifetime production efficiency and grazing utility of sheep. For Sub-objective 1.A, progress was made on developing methods to precisely classify sheep according to the ability to taste bitter flavor, a flavor commonly associated with invasive plant species. Two methods were developed, one using a water and one using a feed test medium, where sheep were offered test mediums with and without a bittering agent in a side-by-side presentation. The results are being prepared for publication. A greater understanding of herbivory choices (forage preference) of sheep will enable grazers and land managers to precisely use sheep to direct rangeland vegetation towards specific biodiversity goals.
In support of Objective 2, research was initiated to evaluate the efficacy of sodium chlorate, a non-antibiotic feed/water additive, to mitigate risk of mastitis in lactating sheep. For Sub-objective 2.A, ewes were identified, based on breed, age, and health, to be enrolled (spring of 2024) in the project. Sodium chlorate has been shown to decrease Enterobacteriaceae organisms implicated in causing subclinical and clinical mastitis in lactating ewes. Mastitis greatly reduces the productive longevity of a ewe, resulting in premature culling and reduced survivability of their nursing offspring. Antibiotics are the only treatment option available to cure mastitis. Identification of novel non-antibiotic feed and water additives to reduce mastitis would improve producer profitability and reduce antibiotic use.
Accomplishments
1. Targeting bitter threats to rangeland biodiversity. The sagebrush steppe occupies nearly 165 million acres of the U.S. West, providing critical ecosystem services, such as habitat, clean water, greenhouse-gas management, cultural heritage, and food security for the nation. Invasive plants, both native and exotic, are rapidly modifying the sagebrush steppe, resulting in a loss of biodiversity. Vegetation biodiversity is critical towards maximizing provisioning service capacity and resilience of the sagebrush steppe. Small ruminants are commonly used in strategic grazing applications to remove invasive plants. However, traditional “targeted grazing” applications fail to address landscape-scale needs, such as managing vegetation biodiversity. In cooperation with the University of Idaho, researchers at the ARS location in Dubois, Idaho, have set out to apply targeted grazing at a landscape scale through leveraging heritable traits of herbivory and taste preference in sheep to create commercial-scale flocks with predictable preferences for specific plants. This work has resulted in heritability estimates as well as potential genomic markers associated with sheep herbivory, which have application towards vegetation biodiversity management in native rangeland systems.
2. Strengthening genetic connections of U.S. sheep breeds. A lack of genetic relationships across U.S. sheep flocks limits the sheep industry’s ability to conduct national genetic evaluation, which is critical towards advancing the industry. To address this problem, ARS researchers at Dubois, Idaho, Clay Center, Nebraska, and Booneville, Arkansas, are working together to form USDA-managed genetic reference flocks (GRF) where sheep genetic resources are shared among the locations and industry sires from around the nation are incorporated into the flocks. In recent years, breeders of Targhee sheep, a major breed integral to the U.S. sheep industry, expressed a desire to improve productivity and profitability through genetic evaluation. To meet the needs of these stakeholders, GRF researchers completed a multi-year breeding and evaluation project at Dubois, Idaho, to integrate industry genetics on a large-scale basis to provide genetic connectedness needed for national genetic evaluation. Recent completion of this project resulted in the Targhee breed becoming one of the first breeds enrolled in the USDA GRF program. Information learned from this project serves as a model for increasing genetic relationships among other U.S. breeds as the industry moves forward into advanced national genetic evaluation, including genomic selection.
Review Publications
Stegemiller, M.R., Redden, R.R., Notter, D.R., Taylor, T., Taylor, J.B., Cockett, N.E., Heaton, M.P., Kalbfleisch, T.S., Murdoch, B.M. 2023. Using whole genome sequence to compare variant callers and breed differences of US sheep. Frontiers in Genetics. 13. Article 1060882. https://doi.org/10.3389/fgene.2022.1060882.
Southerland, C.N., Taylor, J.B., Yelich, J.V., Ellison, M.J. 2022. Refined methodology for identification of bitterness aversion in mature rams through quantification of fluid intake and behavioral response to phenylthiocarbamide. Applied Animal Behaviour Science. 254. Article 105706. https://doi.org/10.1016/j.applanim.2022.105706.
Wilmer, H.N., McGranahan, D.A., Moffet, C., Taylor, J.B. 2023. Effect of burn season and grazing deferment on mountain big sagebrush plant communities. Plant Ecology. 224:501-512. https://doi.org/10.1007/s11258-023-01317-1.
Hanna, L.L., Taylor, J.B., Holland, P.W., Vonnahme, K.A., Reynolds, L.P., Riley, D.G. 2023. Effect of ewe birth litter size and estimation of genetic parameters on ewe reproductive life traits. Animal. Volume 17(8). Article 100900. https://doi.org/10.1016/j.animal.2023.100900.
