Clustering climate and management practices to define environmental challenges affecting gastrointestinal parasitism in Katahdin sheep

Authors: ARISMAN, BRIAN - University Of Nebraska; Burke, Joan; MORGAN, JAMES - Round Mountain Consulting; LEWIS, RON - University Of Nebraska

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2022
Publication Date: 1/5/2023
Citation: Arisman, B.C., Burke, J.M., Morgan, J.L., Lewis, R.M. 2023. Clustering climate and management practices to define environmental challenges affecting gastrointestinal parasitism in Katahdin sheep. Journal of Animal Science. https://doi.org/10.1093/jas/skad002.
DOI: https://doi.org/10.1093/jas/skad002

Interpretive Summary: Katahdin sheep are a popular maternal hair breed that can exhibit an innate resistance to gastrointestinal nematodes (GIN). Still, the consequences of GIN infection on performance levels even in this breed depend on the climatic and management conditions in which they are raised. Information on management practices in 40 U.S. Katahdin flocks was collected with an online survey. Climate data corresponding with these flock’s locations were gathered from the National Weather Service. Using multivariate analysis to combine these data, 9 distinct eco-management groupings or clusters were identified. These clusters differed in temperature, precipitation, grain supplementation, and the age at which the lambs were introduced to pasture. In 17 of these flocks, traits indicative of GIN parasitism—fecal egg count, FAMACHA score, and body weight—were measured in 90-d old Katahdin lambs. Eco-management cluster explained more variation in performance in all three traits than climate or management alone. Based on fecal egg counts, eco-management clusters corresponding with hotter temperature and greater precipitation, and pasture-born lambs, suffered a greater parasite challenge. Conversely, eco-management clusters with lambs turned out to pasture at older ages benefited from reduced challenge. Eco-management clusters provide a holistic approach to combine environmental factors that predispose lambs to parasitism.

Technical Abstract: Gastrointestinal nematodes (GIN) negatively affect the performance and wellbeing of sheep. Due to anthelmintic resistance, GIN are difficult to control leading producers to choose breeds that are naturally resistant. An example is Katahdin sheep. Katahdin are raised in various climates and management systems in the U.S. These environmental factors can be combined to form eco-management groupings or clusters. We hypothesized that GIN challenge varies predictably based on the characteristics of these environmental clusters. Forty Katahdin producers from across the U.S. were surveyed for management information. Body weights (BW), FAMACHA scores (FAM), and fecal egg counts (FEC) were collected on 3,426 lambs around 90 d of age from 17 of the flocks. Management and climate data were combined into clusters using Multiple Correspondence and Principal Component (PC) analysis. Performance data were aligned with their corresponding cluster. Depending on the trait, eco-management cluster, birth-rearing type, sex, and, as covariates, dam age, were fitted as systematic effects with ANOVA. Clusters also were formed based on climate or management data alone. When compared with fitting the eco-management clusters, they defined less variation in each of the traits based on Akaike and Bayesian information criterion, and adjusted r2 values. To further examine variation defined by eco-management clusters, residuals from an ANOVA model excluding eco-management cluster were retained, and their correlation with PC loadings calculated. All PC loadings were included as potential independent variables and tested for significance using backward stepwise regression. The PC loadings with a correlation |=0.49| explained significant variation in each trait and were included in the final models chosen; adjusted r2 values for BW, FEC, and FAM were 0.90, 0.81, and 0.97, respectively. When analyzing GIN challenge, eco-management clusters corresponding with hotter temperatures and greater precipitations, and pasture-born lambs, suffered a greater parasite challenge. Conversely, the eco-management clusters with lambs turned out to pasture at older ages benefited from reduced challenge. Through the formation of eco-management clusters, an environmental variable can be defined to study interactions of genotypes to their environment, providing a potentially useful tool for identifying parasite-resistant sheep.