Project Number: 2056-31610-006-21-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Jul 29, 2019
End Date: Jul 29, 2020
Objectives: 1) Calculate breed differences and heterosis for sheep breeds and breed crosses for longevity, performance, and product traits; 2) Evaluate different measures/classifications for ewe longevity and lifetime production; 3) Estimate genetic correlations between female longevity and production traits (mature size, early growth, scrotal circumference). 4) Develop unique adjustments for potential heterogeneous variances and environmental effects that may be necessary when combining pure and crossbred data.
The ARS-RSPER Sheep Genetics Database (SGD) was initiated in 1912. All composite breeds (e.g., Columbia, Targhee, Polypay, and a new terminal-sire breed) developed at RSPER-US Sheep Experiment Station and all foundation pure breeds used in the development are in the SGD. Multiple attributes, including those used in LambPlan-NSIP, are recorded in the SGD. The SGD will be used to accomplish the objectives. The focus will be specifically on the breeds: Targhee, Rambouillet, Polypay, Suffolk, Columbia, the new RSPER terminal-sire compsite breed, and all breed crosses. Initially, attribute codes for culling (removal from the flock), which vary considerably, will be reassessed for accuracy and grouped according to likeness. This will increase precision of determining the true nature of culling. Once completed, an analysis will be conducted to determine culling codes most associated with ewe longevity and stayability. Random regression models will be constructed to estimate stayability and also novel traits related to lifetime production, such as number of lifetime lambs born or cumulative number of days lactating. Lifetime lambs may need to be censored at 2 or 3 lambs per lambing to prevent extreme selection for too many lambs. Days lactating would identify ewes that lamb early in the season, meaning they breed back faster and likely have heavier lambs at weaning. The genetic correlations between these traits and other production traits related to growth, fertility, and(or) product quality will be useful to understand any potential correlated responses to selection for longevity. If any of those traits are highly correlated, those traits will be incorporated into multiple trait models to improve accuracy of longevity evaluations. Cooperators will utilize existing data from the SGD that were generated from crossbreeding projects undertaken at RSPER over the last three program cycles. Rams of multiple breeds, meat- and wool-type, were purchased from around the nation and crossed to the RSPER’s ewe base. This has resulted in an unparalleled crossbred record database, representing nearly 240 sires and their offspring’s performance for an array of economically relevant traits. Information on the newly formed Terminal-sire composite line, and an industry composite (Siremax), is also available for comparative purposes. Using quantitative genetics methods, breed effects will be determined. Based on the population’s structure, including mating design, direct and maternal heterotic effects from the various crosses will be evaluated. Since purebred sires were sourced from flocks participating in the National Sheep Improvement Program (NSIP), the crossbred data will be connected with purebred parental performance.