TEMPORAL CONTIGUITY BETWEEN FOOD INGESTION AND TOXICOSIS AFFECTS THE ACQUISITION OF FOOD AVERSIONS IN SHEEP

How quickly toxins can cause ruminants to acquire food aversions has not been studied. Thus, our objectives were to determine the relationship between the time when the toxin lithium chloride (LiCl) was given and when food aversions were acquired by sheep, and to assess when peak levels of Li in the rumen occurred following different methods of administrating LiCl (dissolved in an aqueous solution vs a dry salt in a dissolvable gelatin capsule). In Experiment 1, when sheep were gavaged with LiCl (150 mg kg-1 body-weight (BW) in 100 ml water) at either 2, 1 or 0 h prior to ingesting oat chaff, only sheep that received LiCl at time 0 h acquired an aversion to oat chaff, which indicates that the aversion-inducing effects of LiCl occurred within 1 h of its administration. To further assess the relationship between food ingestion, the onset of toxicosis and the acquisition of food aversions, two additional experiments were conducted. In Experiment 2, when sheep ate two familiar foods, alfalfa-grain pellets from 08:00 to 08:20 h and oat chaff from 08:30 to 10:30 h, and LiCl was ingested with the pellets, sheep acquired an aversion to the pellets, apparently because the aversion-inducing effects of LiCl occurred shortly after the sheep ate the pellets. Li concentrations in the rumen peaked within 15 min when a solution of LiCl was put directly into the rumen. Conversely, in Experiment 3, when sheep ate alfalfa-grain pellets from 08:00 to 08:20 h, then received a slowly dissolvable gelatin capsule containing LiCl and then ate oat chaff from 08:30 to 10:30 h, they acquired an aversion to oat chaff, evidently because the aversion-inducing effects of LiCl occurred coincident with eating the oat chaff. Li concentrations in the rumen peaked after just 1 h when LiCl was given in a gelatin capsule. In summary, sheep experienced the effects of Li within 1 h after it was dispersed in the rumen, which occurred at different times depending on whether LiCl was mixed with the food or administered in capsules, and the acquisition of an aversion to one of two familiar foods depended on the contiguity between food ingestion and when LiCl had its effects.