Ability of apomorphine and lithium chloride to create food aversions in cattle

Abstract

Lithium chloride is the most common emetic used to create food aversions in laboratory animals and livestock. However, it is slowly excreted or metabolized, and requires several days for animals to recover. Because of its caustic nature and the large quantities required by cattle and sheep, lithium is best administered directly into the rumen and diluted by rumen fluid. The objective of this study was to evaluate apomorphine as an alternative emetic to create food aversions in cattle. A pilot study showed doses of apomorphine at 0.2 mg/kg BW caused some discomfort in cattle. Doses of 0.4 mg/kg BW and above resulted in severe intoxication and excessive discomfort. We then compared intramuscular injection of apomorphine at 0.1 and 0.2 mg/kg BW, to the standard dose of lithium chloride (200 mg/kg BW by gavage), and to a control treatment (200 ml water by gavage). Four heifers (428 kg) were randomly placed in each group. The heifers consumed flavored alfalfa pellets for 5 min, then were restrained in a chute and administered the respective treatment. The strength and longevity of the aversion was tested by offering the flavored pellets in single-choice extinction trials for six days. The Lithium group did not consume any flavored pellets, thus maintaining a total aversion. Both apomorphine groups reduced consumption to 40% of baseline intake, but the aversion extinguished by the end of the trial. There was no difference between the two apomorphine doses. Under these conditions, lithium chloride is superior to apomorphine in creating and maintaining taste aversions in cattle.