Diet and habitat selection by cattle: The relationship between skin- and gut-defense systems

Animals possess an external or skin-defense system that protects them from aggressions inflicted by predators, and an internal or gut-defense system that deters them from over-ingesting toxins. We conducted a study with cattle to investigate the relation between skin- and gut-defense systems and their influence on diet and habitat selection. Sixteen yearling steers were randomly assigned to one of four treatment groups and were exposed individually to an experimental arena during multiple 10 min trials during which they were allowed to select between an unsafe high quality habitat (UHQ) surrounded by traffic cones (visual cues), a safe, uncued high quality habitat (SHQ), or a safe, uncued moderate quality habitat (SMQ). Experimental habitats were made up of groups of bowls containing barley and oat grain (UHQ and SHQ habitats) or Bermuda grass hay (SMQ habitat). Treatments consisted of no aversions (control group), or of averted groups using: (a) electric shock; (b) lithium chloride (LiCl); or (c) both LiCl and electric shock. Steers in the shock group avoided UHQ almost completely, spending significantly less time there than control steers (P<0.05), but consumed as much HQ forage from SHQ habitat as control steers. Thus, steers in this group did not become averted to the HQ food in uncued locations. Moreover, location avoidance of steers in this group did not extinguish after shock collars were removed or when location of the UHQ habitat was switched. Steers in the LiCl group consumed significantly less HQ forage than control steers, both in UHQ habitat and SHQ habitat, and spent significantly less time than control steers in UHQ and SHQ habitats. Whereas food aversion remained unchanged during experimentation and extinction trials, location avoidance of steers in the LiCl group rapidly extinguished when location of habitats was switched. Thus, steers averted with LiCl avoided HQ food irrespective of its location or association with visual cues. Steers in the LiCl+shock group almost completely avoided HQ forage in UHQ and SHQ habitats and spent less time than the control steers in both of these habitats. The pattern of extinction of steers in this group was the same as in steers in the LiCl group.