Responsiveness of domesticated goats towards various stressors following long-term cognitive test exposure

Abstract

Current evidence suggests that frequent exposure to situations in which captive animals can solve cognitive tasks may have positive effects on stress responsiveness and thus on welfare. However, confounding factors often hamper the interpretation of study results. In this study, we used human-presented object-choice tests (in form of visual discrimination and reversal learning tests and a cognitive test battery), to assess the effect of long-term cognitive stimulation (44 sessions over 4-5 months) on behavioural and cardiac responses of female domestic goats in subsequent stress tests. To disentangle whether cognitive stimulation per se or the reward associated with the human-animal interaction required for testing was affecting the stress responsiveness, we conditioned three treatment groups: goats that were isolated for participation in human-presented cognitive tests and rewarded with food ('Cognitive', COG treatment), goats that were isolated as for the test exposure and rewarded with food by the experimenter without being administered the object-choice tests ('Positive', POS treatment), and goats that were isolated in the same test room but neither received a reward nor were administered the tests ('Isolation', ISO treatment). All treatment groups were subsequently tested in four stress tests: a novel arena test, a novel object test, a novel human test, and a weighing test in which goats had to enter and exit a scale cage. All treatment groups weretested at the same two research sites, each using two selection lines, namely dwarf goats, not selected for production traits, and dairy goats, selected for high productivity. Analysing the data with principal component analysis and linear mixed-effects models, we did not find evidence that cognitive testing per se (COG-POS contrast) reduces stress responsiveness of goats in subsequent stress tests. However, for dwarf goats but not for dairy goats, we found support for an effect of reward-associated human-animal interactions (POS-ISO contrast) at least for some stress test measures. Our results highlight the need to consider ontogenetic and genetic variation when assessing stress responsiveness and when interacting with goats.

Keywords: Animal cognition; Animal handling; Habituation; Selection for productivity; Stress.

Figure 1. Picture of the arena (3 × 5 m) used for the novel arena test (NA), novel object test (NO), and novel human test (NH). The arena was divided in 12 segments which were drawn on the floor.

The numbering shown was used to identify the segments when encoding the animals.

Figure 2. Picture of a dairy goat standing on the scale and wearing the harness used to record cardiac measures.

Figure 3. Biplots of the principal component analysis for each of the four stress tests: novel arena test (NA), novel object test (NO), novel human test (NH), and weighing test (WH).

Figure 4. Treatment (COG, POS, ISO) fixed effect estimates with confidence intervals from linear mixed-effects models with component scores from principal component analyses as responses.

Distributions of component scores (grey dots) are summarised as rotated kernels.