Effect of breed and lithium chloride dose on the conditioned aversion to olive tree leaves (Olea europaea L.) of sheep

• The response of 3 sheep breeds to 2 LiCl doses for inducing conditioned aversion to olive tree leaves was evaluated.
• Different neophobic feeding behaviour was observed according to breed.
• Sensitivity to LiCl depends on sheep breed and dose used.

Grazing maybe an efficient tool for controlling weed cover in olive groves. However, olive leaves are very palatable for sheep, which damages the trees and compromised the later olive production. Lithium chloride (LiCl) is an effective agent for creating food aversion in ruminants through the activation of the emetic system. We investigated the response in three sheep breeds (Manchega, Lacaune and Ripollesa; N = 15 for each breed) to two doses of LiCl (AV1, 200; AV2, 225 mg/kg BW) for averting adult ewes to olive tree leaves compared to a control group (C, water blank). The aversion was reinforced on day 9 in those ewes that consumed >10 g of olive leaves. Persistence was evaluated by a double-choice feeding assay, where 100 g of olive leaves were offered side-by-side with 390 g of rye-grass (as fed), at several intervals across 70 days. Intake and persistence were compared between doses and breeds. Significant breed effects in the controls suggested a genetic component in neophobia (i.e., Ripollesa and Manchega were neophobic whereas Lacaune was not). Aversion was fully created with a single dose in all ewes, however, 20% of animals needed a reinforcement dose to strengthen the aversion (especially in Manchega ewes and AV1 dose). Total aversion persisted 54 days in AV2 and 33 days in AV1, whereas that differences only presented a tendency in Manchega breed (P = 0.058). Effective aversion length of AV1 vs. C varied by breed (Manchega < Lacaune = Ripollesa), but those differences were not detected in AV2 for which all the breeds showed less olive leaf intake until the end of the experiment (day 70, P < 0.001). In conclusion, breed affected aversion persistence at a 200 mg LiCl/kg BW dose. However, a dose of 225 mg LiCl/kg BW with a reinforced dose might mitigate the breed effect.