Estimating the Repeatability of Behavioral Traits in Norduz Sheep Subjected To an Arena Test

Abstract

The objective of this study was to estimate the repeatability of behavioral traits in sheep subjected to a 5-min arena test. Two separate tests were conducted over two years to assess the among-individual consistency of behavioral responses in 68 nonpregnant Norduz ewes (2-5 years of age). During each arena test, five behavioral variables were measured: distance to group sheep (DTG), locomotor activity (LOC), zone boundaries crossed (CRS), vocalization (VOC), escape attempts (ESC). A linear mixed model was used to predict DTG and LOC, while a GLMM with a Poisson distribution was used to predict VOC, CRS, and ESC. Age and year were used as fixed factors in both models. The effect of the year was statistically significant on DTG, LOC, and CRS (P < 0.05). The correlations between traits changed over time. In the first year, DTG had no correlation with other variables. However, DTG had a significant positive correlation with LOC (0.54) and CRS (0.64) in the second year. The repeatability of behavioral variables was estimated as linear mixed-effects models (LMMs) and generalized linear mixed-effects models (GLMMs). To estimate adjusted repeatability, the ewes' age and the year of testing were included as fixed effects. The ID of ewes was included as a random effect in all models. The effect of age was statistically significant on LOC and CRS (P < 0.05). The repeatability of behavioral variables varied from the lowest for the ESC (R = 0.10; 95 % CI [0.000, 0.389], P = 0.319) to the highest for the VOC (R = 0.38; 95 % CI [0.054, 0.614], P = 0.006). These results indicate the consistency of among-individual variation in sheep be-haviors that was measured in the arena test.