Conditioned aversion to woody crops in small ruminants

Student thesis: Doctoral thesis

Abstract

This thesis aimed to evaluate the suitability of conditioned taste aversion (CTA), based on the use of lithium chloride (LiCl), to prevent grazing damages in woody crops (i.e., olive groves and vineyards). The CTA is an associative learning behaviour in which an animal avoids consuming a particular feed previously paired with an inductor agent (i.e., LiCl). Currently, grazing sheep and goat for controlling ground cover in crops is not suitable because leaves and stems of woody plants are very palatable for them. In Exp. 1, CTA against olive leaves (novel feed) was induced with a single LiCl dose (200 mg/kg BW) in goats (n = 10) and sheep (n = 10). Aversion was validated individually during the first 6 d and persistence for 4 mo. Ewes and does maintained complete aversion (intake 0 g) until d 23 and 53, respectively (P < 0.05) but their intake was markedly lower (ewes, 40 vs. 83 g; does, 24 vs. 60 g) than control animals throughout the experiment (P < 0.05). A single dose of LiCl was effective to induce CTA against olive leaf, does being more strongly averted than ewes. In Exp. 2, CTA against olive leaves (novel feed) was induced in ewes of 3 breeds (Manchega, Lacaune and Ripollesa; n = 15 for each breed) using different LiCl doses (AV1 and AV2, 200 and 225 mg/kg BW). Ewes that consumed >10 g of olive leaves received a 2nd dose on d 9. Persistence was evaluated by a double-choice feeding assay with rye-grass trough 70 d. Effective aversion length varied by breed (Manchega < Lacaune = Ripollesa) for AV1, but no differences were detected for AV2. We concluded that the 225 mg LiCl/kg BW dose was effective for the 3 breeds. In Exp. 3, long-term CTA (3 yr) against grapevine leaves (novel feed) was induced in ewes of 2 breeds (Lacaune and Manchega; n = 12 for each breed) with a single dose of LiCl (225 mg/kg BW). Effectiveness of CTA was validated under experimental (yr 1) and commercial vineyard conditions (yr 2 and 3). The CTA ewes showed a complete aversion against grapevines throughout yr 1 but a new LiCl dose were needed to maintain CTA during yr 2 and 3. Grazing CTA ewes reduced grass cover between vine lines by 68 and 44% (DM basis), yr 2 and 3, respectively. The use of CTA was effective for controlling ground cover in vineyards. In Exp. 4, Li concentration was measured over 168 h (lactating does; n = 6) and 192 h (dry ewes; n = 6) in plasma, urine, faeces, and milk after a single LiCl dose of 200 and 225 mg/kg BW for does and ewes, respectively. Plasma Li concentrations peaked at 4 h in does and 12 h in ewes, according to their physiological stage. The calculated plasma half-lives were 40.3 and 30.9 h, for does and ewes, respectively. In goats, all Li administered was recovered at 96 h (urine, 92%; faeces, 6.5%; milk, 2.8%); however, the estimated clearance time established by faeces was 11 and 9 d for does and ewes, respectively. Consequently, the use of LiCl was considered as safe and suitable for inducing CTA in small ruminants. In conclusion, induced CTA with LiCl in sheep and goats could be used as an alternative for controlling the ground cover in olive groves and vineyards, without expected damages to the trees and vines during grazing.
Date of Award29 Oct 2014
Original languageEnglish
Awarding Institution
  • Universitat Autònoma de Barcelona (UAB)
SupervisorElena Albanell Trullas (Director) & Gerardo Caja Lopez (Director)

Keywords

  • Lithium chloride
  • Conditioned taste aversion
  • Selective grazing

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