Cognition and behavior in sheep repetitively inoculated with aluminum adjuvant-containing vaccines or aluminum adjuvant only

Abstract

Sheep health management strategies often include the use of aluminum (Al)-containing vaccines. These products were associated with the appearance of the ovine autoimmune/inflammatory syndrome induced by adjuvants (ASIA syndrome), which included an array of ethological changes in the affected animals. The aim of this pilot study was to investigate cognitive and behavioral changes in sheep subjected to a protocol of repetitive inoculation with Al-containing products. Twenty-one lambs were assigned to three groups (n = 7 each): Control, Adjuvant-only, and Vaccine. Vaccine group was inoculated with commercial Al- hydroxide containing vaccines; Adjuvant-only group received the equivalent dose of Al only (Alhydrogel®), and Control group received Phosphate-buffered saline. Sixteen inoculations were administered within a 349-day period. Ethological changes were studied in late summer (7 inoculations) and mid-winter (16 inoculations). Animals in Vaccine and Adjuvant-only groups exhibited individual and social behavioral changes. Affiliative interactions were significantly reduced, and aggressive interactions and stereotypies increased significantly. They also exhibited a significant increase in excitatory behavior and compulsive eating. There were increased levels of stress biomarkers in these two groups. In general, changes were more pronounced in the Vaccine group than they were in the Adjuvant-only group. Some changes were already significant in summer, after seven inoculations only. This study is the first to describe behavioral changes in sheep after having received repetitive injections of Al-containing products, and may explain some of the clinical signs observed in ovine ASIA syndrome.