Conditioned aversion to olive tree leaves (Olea europaea L.) in goats and sheep

With the aim of adverting to olive tree leaves, lithium chloride (LiCl) was used in goats and sheep. A total of 10 dairy does (Murciano-Granadina breed) and 10 dairy ewes (Manchega breed) were used in 2 simultaneous experiments for comparing olive leaf intake in averted vs. control animals. Does and ewes were dry and non-pregnant and were randomly allocated into 4 experimental groups of 5 animals each. Animals had no previous contact with olive leaves. For aversion induction, all animals were penned in individual box stalls during 6 d, fed tall fescue hay ad libitum, and offered the olive leaves for 5 min (does) or 1 h (ewes). Aversion was induced by using a drenching gun for orally administering a solution of LiCl (200 mg/kg BW) in water, immediately following olive leaf consumption in the averted groups. Water alone was drenched in the control groups as a blank. Does learned faster to eat the olive leaves and developed stronger aversion to the LiCl treatment than ewes. After the aversion induction period, all the animals joined their respective flock or herd, grazed a cultivated pasture during the day and were complemented indoors with tall fescue hay during the night. Aversion memory was evaluated every 14 d via of 5 min lasting 144 d in the does, and 10 min lasting 130 d in the ewes. No LiCl was given during the aversion memory test period. No olive tree leaf consumption was detected until day 53 and 23, for does and ewes, respectively (P < 0.05). Olive tree leaf consumption in the averted groups was lower than in the control groups throughout the experiment (P < 0.05). Animal behavior, when the olive leaves were offered, differed between averted and control groups during learning and memory test periods. Animals in the control group avidly ate the olive leaves, whereas animals in the averted groups strongly rejected the olive leaves. In conclusion, the LiCl conditioned aversion to olive tree leaves proved to be an efficient short-term method in sheep and goats under our experimental conditions. The method may be of special interest for implementing selective grazing and for avoiding the use of herbicides in organic cultures. Further research will be necessary before recommending its use in practice. (C) 2010 Elsevier B.V. All rights reserved.