216 Using GPS collars and vaginal temperature sensors for characterizing rangeland usage and climatic stress in sheep

Abstract

Abstract Increased climatic variability represents the most significant threat to arid rangeland production systems. We set out to describe land use behavior of rangeland sheep and associations between land use phenotypes and body weight (BW) gain via the investigation of GPS data paired with vaginal temperature sensors to characterize fitness under climatic stress. During a fortnight spanning Aug 19th to Sep 1st, 2023, we deployed 200 vaginal temperature sensors and 199 GPS collars on extensively managed Australian Merinos, and a ⅝ Merino X ⅜ Rambouillet composite line in central Nevada, totaling 200 sampled individuals. Vaginal temperature sensors were constructed by affixing Thermochron iButtons to small ruminant CIDRs depleted of progesterone. GPS collars were constructed by enclosing i-gotU GT-120B GPS units in rubber shrink tubing around large dog collars. The iButtons sampled for vaginal temperature every 10 min, and the GPS collars sampled for location every 5 min. Body weights were recorded at the beginning and end of the trial. Remotely sensed data were acquired from the USGS and climateengine.org to analyze covariates such as slope and elevation, and NDVI, and climate, respectively, and were combined with observational data to generate rasters of distance from water and shade. GPS Position was continuously modeled using the R package momentuHMM (function crwWrap) to allow for the union of simultaneous temperature and location observations. A hidden markov model was employed (function fitHMM) to delineate between active and resting observations. Estimates were more significant when modeling land use and temperature phenotypes by just “active” observations. We used a forward progressing model building function with the R package leaps (function regsubsets) to associate weight change with all land use and temperature phenotypes. Logged distance to shade (P = 0.023) and vertical distance traveled (P = 0.057) were associated with BW gain. The square root of the range in vaginal temperature was positively associated with BW gain (P = 0.045) in a simple linear regression model, suggesting that the ability to adapt to heat stress via metabolic elasticity increases fitness. This study also estimated repeatability for land use behavior and temperature traits. The repeatabilities for vertical distance traveled and distance to shade were 0.20 ± 0.03 and 0.04 ± 0.01, respectively. The repeatabilities for mean temperature and vaginal temperature range were 0.47 ± 0.03 and 0.26 ± 0.03, respectively. In conclusion, some land use traits are lowly to moderately repeatable and have significant relationships to BW gain (i.e., fitness) in rangeland settings. Temperature traits are moderately to highly repeatable and can be associated with BW gain.