Location: Livestock Bio-Systems
2021 Annual Report
Objectives
Objective 1: Perform genetic analyses, including genomics and genetic parameters, for a suite of health and performance traits (e.g. mastitis, respiratory disease, milk quality and eating quality).
Objective 2: Evaluate impact of TMEM154 genetic variants on lifetime productivity of sheep.
Approach
The proposed plan will develop comprehensive phenotyped populations in which the effects of genomic variation can be estimated and selection can be performed to improve animal growth and reproductive performance. This approach will generate genomic technologies to increase production efficiency for release to sheep producers.
Progress Report
In support of Objective 1, three multi-year experiments to collect data on economically important health, performance, and behavioral traits were initiated in Fiscal Year (FY) 2021. The first experiment began phenotyping Katahdin lambs in FY2021 for feed intake, growth, health, and carcass traits (approximately 120 lambs per year). This experiment, along with another initiated in FY 2020 which phenotypes Katahdin ewes for health and longevity traits (approximately 300 ewes per year), is part of a multiple ARS location effort to evaluate novel traits for suitability in the National Sheep Improvement Program (NSIP). Currently, the NSIP generates estimated breeding values for traits that can be readily measured on farm/ranch (e.g., ewe fecundity, lamb weight, etc.). However, many other traits impact sheep enterprise profitability but are too difficult/expensive for producers to measure (e.g., health, longevity, feed efficiency, carcass traits, etc.). By ensuring strong genetic connectedness between ARS and industry purebred sheep flocks, ARS researchers and collaborators can evaluate novel traits for use in the NSIP. Two other experiments were initiated in FY 2021 in the Composite IV sheep population. Ram breeding capacity (number of ewes mated) is an economically important trait to sheep producers, particularly those that expose ewes to multiple ram mating groups. Past work has estimated large variation in breeding capacity among fertile rams, which indicates that behaviors toward ewes and other rams have important roles. Composite IV rams were fitted with accelerometers and exposed to small groups of estrus-synchronized ewes for short duration by themselves or with two other rams and behaviors were video recorded. Rams were again fitted with accelerometers and exposed to a larger group of ewes (3 rams:50 ewes) for a 21-d breeding season. Determination of sires of lambs is documented by genomic testing of progeny DNA using a panel of parentage markers. Collected data will enable researchers to identify behavioral characteristics that are indicative of more successful ram mating behavior. The second experiment utilizing the same Composite IV sheep will seek to quantify maternal and neonatal behaviors as well as dam mammary health and conformation traits which contribute to lamb survival in low-input, pasture lambing systems. Low-input production systems are well suited to sheep managed on marginal landscapes but reduce the ability to observe and measure traits that are more easily recorded on sheep managed in varying degrees of confinement. This experiment is a cross-over design which will allocate genetically related ewes to be represented within barn or pasture lambing groups each year. Ewes in the barn lambing group are placed under camera observation to record maternal and lamb behavior. Samples are collected on this subset of ewes to infer colostrum quality and immune transfer to lambs as well as ewe udder health and conformation. Data from these experiments will be used to estimate genetic effects/genomic regions contributing to variation in economically important ewe, ram, and lamb traits. Results will be evaluated for their application to the sheep industry in the form of new genetic tools for stakeholder use.
In support of Objective 2, analysis of data was completed for the first of three prospective experiments designed to evaluate the relative impact of four of the most common genetic variants for the TMEM154 gene in U.S. sheep populations on ewe lifetime productivity. These novel experiments were the first and only example of their kind to evaluate ewes with specific haplotype combinations for TMEM154 yet with a common genetic and management background with repeated performance records and multiple sampling points to establish when infections were initially observed. Prior experiments have always evaluated a snapshot in time for a population. Analysis of the first experiment compared performance of ewes with the least susceptible haplotype variant 1 compared to the common ancestral haplotype variant 3 (see listed accomplishment). The second experiment directly compared the impact of haplotype 2 compared to haplotype 3 which are both highly susceptible to infection to the virus causing ovine progressive pneumonia (OPP). In the third and final experiment, ewes with haplotype 1 are compared to ewes with haplotype 4 which are both less susceptible to infection by the virus. These combined analyses will provide the sheep industry with comprehensive recommendations for both management systems and genetic selection programs using TMEM154 variants to help mitigate the effects of OPP.
Accomplishments
1. Impact of two genetic variants on ewe lifetime productivity. Susceptibility to a virus that causes ovine progressive pneumonia (OPP) that results in multi-million dollar losses to the sheep industry is associated with genotypes at the TMEM154 gene. ARS researchers at Clay Center, Nebraska interpreted data from a novel prospective study specifically designed to evaluate the effects of each genotype combination, or diplotype, on infection status and ewe lifetime productivity. In a common environment and with similar levels of natural virus exposure, less than 10% of diplotype “1,1” ewes became infected through 5.5 yr of age whereas > 80% of diplotype “1,3” and “3,3” ewes were infected by 3.3 yr of age. Over five production years, diplotype “1,1” ewes weaned, on average, 2.1 more lambs and 40 kg greater weight of lamb than diplotype “1,3” and “3,3” ewes. Using average economic conditions during this experiment, this equates to $171 in additional lifetime revenue per TMEM154 diplotype “1,1” ewe, resulting in multi-million dollars of increased revenue across the industry. Increasing the frequency of TMEM154 haplotype “1” within a flock promotes genetic resilience to OPP and should be utilized by producers seeking to mitigate the effects of this costly disease.
Review Publications
Murphy, T.W., Freking, B.A. 2021. Comparison of performance of F1 Romanov crossbred ewes with wool and hair breeds during fall lambing and body weight and longevity through six production years. Journal of Animal Science. 99(1):1-7. https://doi.org/10.1093/jas/skaa400.
Murphy Jr, T.W., Keele, J.W., Freking, B.A. 2020. Genetic and nongenetic factors influencing ewe prolificacy and lamb body weight in a closed Romanov flock. Journal of Animal Science. 98(9):1-8. https://doi.org/10.1093/jas/skaa283.
Thorne, J.W., Murdoch, B.M., Freking, B.A., Redden, R.R., Murphy Jr, T.W., Taylor, J.B., Blackburn, H.D. 2021. Evolution of the sheep industry and genetic research in the United States: Opportunities for convergence in the 21st century. Animal Genetics. 52(4):395-408. https://doi.org/10.1111/age.13067.
Stewart, W.C., Murphy Jr, T.W., Page, C.M., Rule, D.C., Taylor, J.B., Austin, K., Pankey, C. 2020. Effect of increasing dietary zinc sulfate fed to primiparous ewes: I. Effects on serum metabolites, mineral transfer efficiency, and animal performance. Applied Animal Science. 36(6):839-850. https://doi.org/10.15232/aas.2020-02057.
Stewart, W.C., Scott, D.M., Howell, S.B., Kaplan, R.M., Roeder, B.L., Murphy, T.W. 2020. Anthelmintic resistance in gastrointestinal nematodes and associated management factors in Intermountain West sheep flocks. Sheep and Goat Research Journal. 35:30-37.
Knuth, R.M., Stewart, W.C., Taylor, J.B., Bisha, B., Yeoman, C.J., Van Emon, M.L., Murphy, T.W. 2021. Relationships among intramammary health, udder and teat characteristics, and productivity of extensively managed ewes. Journal of Animal Science. 99(4):1-10. https://doi.org/10.1093/jas/skab059.
Stewart, W.C., Scasta, J.D., Taylor, J.B., Murphy Jr, T.W., Julian, A.A. 2021. Invited Review: Sheep mineral nutrition considerations for extensive production systems. Applied Animal Science. 37(3):256-272. https://doi.org/10.15232/aas.2021-02143.
Lindo, A.N., Thorson, J., Bedenbaugh, M.N., Mccosh, R.B., Lopez, J.A., Young, S.A., Meadows, L.J., Bowdridge, E.C., Fergani, C., Freking, B.A., Lehman, M.N., Hileman, S.M., Lents, C.A. 2021. Localization of kisspeptin, NKB, and NK3R in the hypothalamus of gilts treated with the progestin altrenogest. Biology of Reproduction. Article 103. https://doi.org/10.1093/biolre/ioab103.
