Conditioned aversion to woody crops in small ruminants

Abstract

L'objectiu de la tesi va ser avaluar la idoneïtat de l'aversió condicionada (CTA) amb clorur de liti (LiCl), per evitar danys en cultius llenyosos durant el pasturatge de les cobertes vegetals. La CTA és un aprenentatge associatiu pel qual un animal deixa de consumir un aliment gràcies a l'administració d'un agent inductor (LiCl). Actualment, els agricultors no permeten el pasturatge de les cobertes dels cultius llenyosos per l’alta palatabilitat d’aquests. A l’Exp. 1, es va crear CTA a l'olivera (aliment nou) amb una sola dosi de LiCl (200 mg/kg PV) en cabres (n = 10) i ovelles (n = 10). L'aversió es va comprovar durant els primers 6 d, i la persistència durant 4 mesos. Les ovelles i cabres van rebutjar completament el consum d'olivera durant 23 i 53 d (P < 0.05), respectivament, i van consumir una quantitat inferior als animals control fins al final de l'experiment (ovelles, 40 vs. 83 g, cabres, 24 vs. 60 g; P < 0.05). Una sola dosi de LiCl va ser efectiva per induir CTA l'olivera, presentant major aversió les cabres que les ovelles. A l’Exp. 2, es va crear aversió a l'olivera en 3 races d'ovelles (Manxega, Lacaune i Ripollesa; n = 15 per raça) utilitzant diferents dosis de LiCl (AV1 i AV2, 200 i 225 mg/kg PV). Les ovelles que van consumir > 10 g d'olivera van rebre una 2a dosi el d 9. La persistència de la CTA es va avaluar oferint com a aliment alternatiu rye-grass durant 70 d. La persistència per AV1 va variar en funció de la raça (Manxega < Lacaune = Ripollesa), mentre que per AV2 no es van detectar diferències. Els resultats van indicar que la dosi de 225 mg LiCl/kg PV va ser igual d'eficaç per les 3 races. A l’Exp. 3, es va crear CTA de llarga durada (3 anys) a la vinya (aliment nou) en dues races d'ovelles (Lacaune i Manxega; n = 12 per raça) amb una sola dosi de LiCl (225 mg/kg PV). L'efectivitat de la CTA va ser validada en condicions experimentals (any 1) i de vinya comercial (any 2 i 3). Les ovelles CTA van rebutjar totalment consumir les fulles de vinya durant el 1er any, però va ser necessària una 2a dosi de LiCl per mantenir la CTA durant el 2n i 3er any. La coberta vegetal de la vinya es va reduir un 68 i 44% (base MS) com a conseqüència del pasturatge en els anys 2 i 3, respectivament. A l’Exp. 4, es va mesurar la concentració de Li durant 168 h (cabres en lactació, n = 6) i 192 h (ovelles seques, n = 6) en plasma, orina, femta i llet després de l'administració d'una dosi de LiCl (200 i 225 mg/kg PV per cabres i ovelles, respectivament). Les concentracions plasmàtiques de Li arribar al seu màxim a les 4 h en cabres i 12 h en ovelles. La semivida de Li calculada en plasma va ser de 40,3 i 30,9 h, en cabres i ovelles, respectivament. En les cabres, es va recuperar tot el Li administrat a les 96 h (orina, 92%, femtes, 6,5%; llet, 2,8%); però, el temps d'eliminació estimat establert per la femta va ser del 11 i el 9 d en cabres i ovelles, respectivament. Conseqüentment, l'ús de LiCl es va considerar segur i adequat per induir CTA en els petits remugants. En conclusió, la CTA induïda amb LiCl en ovelles i cabres podria utilitzar-se com a alternativa per al control de la coberta vegetal en oliveres i vinyes, sense danyar-los durant el pasturatge.

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.