Concentrations of faecal glucocorticoid metabolites in South African Mutton Merino sheep fed various sources of roughage

Abstract

The objective of this study was to determine whether various sources of roughage in nutritionally balanced feedlot diets would evoke a stress response in sheep. A nutritional stress response test was performed on 20 ewes, randomly divided into four treatment groups with 5 ewes per group. Ewes were kept individually in metabolic crates for thirty days. Rations were balanced nutritionally, and various sources of roughage were included; T1: alfalfa hay, T2: maize stover, T3: soya hulls; and T4: Eragrostis tef. Faeces was removed manually from the caudal rectum of each ewe at 05h00 and 19h00. Samples were frozen at -20°C until analyses. A total of 520 faecal samples were analysed to determine the concentrations of faecal glucocorticoid metabolites (fGCM) by enzyme immunoassay (EIA). These concentrations were expressed as mass/g dry weight (ng/g DW). Baseline values were determined, and those greater than the mean plus 2 standard deviations were removed. Baseline values were compared between the groups with one-way ANOVA analysis. The average concentrations of fGCM were 178.77 ± 21.7 in the morning and 183.2 ± 14.4 in the evening. Sheep fed T4 had significantly higher fGCM concentrations in both morning (302.0 ± 86.1 ng/g DW) and evening (237.0 ± 48.1 ng/g DW) compared with the other treatment groups. Thus, fGCM concentrations in sheep were related to the source of roughage, and Eragrostis tef caused a stress response.

Keywords: animal welfare, cortisol, dietary fibre, selective grazer, stress response