Relationships between temperament, feeding behaviour, social interactions, and stress in lambs adapting to a feedlot environment

Abstract

The production of lamb meat is a large and important industry in Australia. Variability and seasonality of the climate and the demand for a consistent product (in terms of weight and age) have led to an increase in the use of feedlot systems for finishing lambs. While most lambs acclimatise to this environment, an estimated 5–20% may suffer from inanition or shy feeding, but there is little direct information available on associated physiological stress. This exploratory study examined relationships between temperament, feeding behaviour, social interactions and cortisol concentrations in lambs in the first 2 weeks in an intensive finishing system (feedlot). Lambs in two 20-lamb feedlots (with 2m2 floor space/animal) were studied. Prior to entry to the feedlot, the lambs were subjected to a temperament test (Isolation Box Test) in which activity was measured. Weight gain, general activity, lying time, time at the feeder, number of feeding bouts, displacement at the feeder and plasma cortisol concentrations in weeks 1 and 2 in the feedlot were recorded. A parsimonious general linear model was developed to relate the logarithm of cortisol concentration in weeks 1 and 2 to all other measurements. In week 1 cortisol was most elevated if the lamb’s activity in the feedlot (number of steps) was low (P=0.000025) and also for those lambs that fed more frequently (P=0.0010). Higher levels of activity in the temperament test were associated with higher cortisol concentrations in week 1 when the lamb was not displaced from the feeder. However there was an interaction with the number of displacements (P=0.0016), leading to little effect when a displacement occurred. In week 2 higher cortisol concentrations were associated with higher growth (P=0.040) which may be a reflection of the positive association between cortisol and feeding bouts in week 1. This study demonstrates relationships between cortisol concentrations, activity in the temperament test, feeding bouts, displacements at the feeder and activity in the first week and growth in the second week in the feedlot. A better understanding of these behaviour and stress relationships early in the feedlot may be useful in identifying strategies to protect vulnerable animals in feedlots.