Continuous exposure to an aversive mixture was investigated as a means of maintaining aversion to vermeerbos in sheep subjected to the social influence of non-averted sheep. The use of an aversive mixture was based on a hypothesis that continuous exposure to an acceptable aversive mixture (containing both the aversive substance and the identification factors of vermeerbos mixed with maize meal) would tempt sheep to consume small quantities of the aversive mixture each day and that this would keep them averted to vermeerbos, despite the social influence of non-averted sheep. Persistent aversion to a vermeerbos-maize meal mixture (1:99 by mass) by sheep continuously exposed to such an aversive mixture, after an initial aversion conditioning with lithium chloride (LiCl, 160 mg/kg BM), was demonstrated. Aversion in adjacent controls not exposed to the aversive mixture only lasted for some time. A similar result was obtained when sheep were challenged for intake of a pure stand of established vermeerbos. Three sheep continuously exposed to an aversive mixture after an initial aversion conditioning totally refused grazing the vermeerbos during a 42-day trial, despite the social influence of three non-averted control sheep grazing vermeerbos on an adjacent site. These results were confirmed by a second replication the following year. Joint grazing for an hour a day by averted and non-averted sheep during the last seven days of this replication also resulted in total avoidance of vermeerbos by the averted animals, despite continued intake of vermeerbos by the control sheep.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. 
Adobe Acrobat v.9 was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201

Kellerman, T. Stephanus

Labuschagne, Leonie

Schultz, R.A. (Rowena Anitra)

Snyman, Leendert D.

Onderstepoort Journal of Veterinary Research

The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. 
Adobe Acrobat v.9 was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.Continuous exposure to an aversive mixture was investigated as a means of maintaining aversion to vermeerbos in sheep subjected to the social influence of non-averted sheep. The use of an aversive mixture was based on a hypothesis that continuous exposure to an acceptable aversive mixture (containing both the aversive substance and the identification factors of vermeerbos mixed with maize meal) would tempt sheep to consume small quantities of the aversive mixture each day and that this would keep them averted to vermeerbos, despite the social influence of non-averted sheep. Persistent aversion to a vermeerbos-maize meal mixture (1:99 by mass) by sheep continuously exposed to such an aversive mixture, after an initial aversion conditioning with lithium chloride (LiCl, 160 mg/kg BM), was demonstrated. Aversion in adjacent controls not exposed to the aversive mixture only lasted for some time. A similar result was obtained when sheep were challenged for intake of a pure stand of established vermeerbos. Three sheep continuously exposed to an aversive mixture after an initial aversion conditioning totally refused grazing the vermeerbos during a 42-day trial, despite the social influence of three non-averted control sheep grazing vermeerbos on an adjacent site. These results were confirmed by a second replication the following year. Joint grazing for an hour a day by averted and non-averted sheep during the last seven days of this replication also resulted in total avoidance of vermeerbos by the averted animals, despite continued intake of vermeerbos by the control sheep.mn201

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Onderstepoort Journal of Veterinary Research, 69:321-325 (2002) Continuous exposure to an aversive mixture as a means of maintaining aversion to vermeerbos (Geigeria ornativa O. Hoffm.) in the presence of non-averted sheep L.D. SNYMAN1, 2 R.A. SCHUL TZ2, T.S. KELLERMAN2,3 and L. LABUSCHAGNE2 ABSTRACT SNYMAN, L.D. , SCHULTZ, A.A., KELLERMAN, T.S. & LABUSCHAGNE, L. 2002. Continuous expo-sure to an aversive mixture as a means of maintaining aversion to vermeerbos (Geigeria ornativa O. Hoffm.) in the presence of non-averted sheep. Onderstepoort Journal of Veterinary Research, 69: 321-325 Continuous exposure to an aversive mixture was investigated as a means of maintaining aversion to vermeerbos in sheep subjected to the social influence of non-averted sheep. The use of an aver-sive mixture was based on a hypothesis that continuous exposure to an acceptable aversive mixture (containing both the aversive substance and the identification factors of vermeerbos mixed with maize meal) would tempt sheep to consume small quantities of the aversive mixture each day and that this would keep them averted to vermeerbos, despite the social influence of non-averted sheep. Persistent aversion to a vermeerbos-maize meal mixture (1 :99 by mass) by sheep continuously exposed to such an aversive mixture, after an initial aversion conditioning with lithium chloride (LiCI , 160 mg/kg BM). was demonstrated. Aversion in adjacent controls not exposed to the aversive mix-ture only lasted for some time. A similar result was obtained when sheep were challenged for intake of a pure stand of established vermeerbos. Three sheep continuously exposed to an aversive mix-ture after an initial aversion conditioning totally refused grazing the vermeerbos during a 42-day trial , despite the social influence of three non-averted control sheep grazing vermeerbos on an adjacent site. These results were confirmed by a second replication the following year. Joint grazing for an hour a day by averted and non-averted sheep during the last seven days of this replication also resulted in total avoidance of vermeerbos by the averted animals, despite continued intake of ver-meerbos by the control sheep Keywords: Aversive mixture, conditioned feed aversion, Geigeria ornativa, plant poisoning, ver-meerbos, vermeersiekte INTRODUCTION Vermeerbos (Geigeria ornativa O. Hoffm.) (Fig. 1) is a non-aversive toxic plant that occurs in the Northern Cape Province of South Africa (Kellerman, Naude & Fourie 1996). Intake of this plant causes vermeer-1 E-mail : Leendert@moon.ovi.ac.za siekte, which amongst other clinical signs such as stiffness, paresis and paralysis, is characterized in sheep by regurgitation of rumen contents through the mouth and nose (Steyn 1949) (Fig. 2). Although it is one of the most important plant poisonings of sheep on the sub-continent (Kellerman, Coetzer & Naude 1988), no effective means for its prevention or treatment has yet been described. 2 Onderstepoort Veterinary Institute, Private Bag X05, Onder-stepoort, 0110 South Africa 3 Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria Accepted for publication 1 October 2002-Editor Conditioned feed aversion has been shown to be a potential management tool to prevent livestock from grazing poisonous plants (Ralphs, Provenza, Pfister, Graham, Duff & Greathouse 2001). Six cows in a small pasture field trial were conditioned 321 Maintaining aversion to vermeerbos (Geigeria ornativa O. Hottm.) in sheep FIG . 1 Vermeerbos (G. ornativa) plant to avoid tall larkspur for three years (Ralphs 1997). However, averted animals had to be grazed sepa-rately from non-averted animals as the induced aversion would be broken down by the social influ-ence of non-averted peers (Ralphs & Olsen 1990; Provenza & Burritt 1991; Ralphs et al. 2001). This means that conditioned feed aversion has no appli-cation to communal grazing systems with sheep of various owners grazing together, mostly on an un-controlled basis. The hypothesis was made that continuous expo-sure to an acceptable aversive mixture, containing both an aversive substance and the identification factors of vermeerbos, mixed with maize meal, would tempt sheep to consume small quantities of the aversive mixture each day and that this would keep them averted to vermeerbos, despite the social influence of non-averted sheep. The workability of this hypothesis was investigated under controlled conditions: (1) with sheep averted to a vermeerbos-maize meal mixture fed under pen-feeding conditions and (2) with sheep averted to a pure stand of established vermeerbos. METHODS AND RESULTS Effect of continuous exposure to an aversive mixture on maintaining aversion to a vermeerbos-maize meal mixture under pen-feeding conditions Duration of aversion to a vermeerbos-maize meal mixture in averted sheep continuously exposed to an aversive mixture was compared with duration of aversion in averted sheep not exposed to an aver-sive mixture. Three successive replications, with two sheep of the same race, gender and age used 322 FIG. 2 Vermeersiekte: regurgitation ot ingesta per replication, were performed. One of the sheep in each replication was exposed to an aversive mix-ture as described below while the other served as control. The two sheep were kept separately in pens adjacent to each other, except for the sheep in repli-cation 1 where aversion in the control sheep and the sheep exposed to the aversive mixture were stud-ied at different times. All sheep received Eragrostis curvula hay ad lib. during the study. During each of the replications sheep were condi-tioned and tested for aversion according to the fol-lowing procedure: 1. Sheep were made accustomed to maize meal by feeding them 100 g each morning for at least a month before commencement of the trial. 2. On day 0 sheep were fed 100 g of a vermeerbos-maize meal mixture (1 :99 by mass) (vermeerbos dried and milled through a sieve with 1 mm aper-ture size) in the feeding trough. 3. Directly after consumption of the vermeerbos-maize meal mixture, which took less than an hour, the sheep were dosed with 160 mg lithium chloride (LiCI) per kg body mass (BM) via a stomach tube. 4. Dosing with LiCI was followed by giving a table-spoon of dry milled vermeerbos in the sheep's mouth. This was done to accomplish a strong taste association with the adverse effect of LiCI. 5. One of the sheep in each replication was con-tinuously exposed to an aversive mixture from day 1. The aversive mixture, consisting of LiCI (AR grade crystals of c. 0.5 mm diameter) mixed with "milled, dry vermeerbos and maize meal (5:1 :94 by mass), was presented ad lib. in a separate feeding-trough. The LiCI-vermeerbos portion of this mixture was started at one fifth this concentration and increased with another fifth every time more than 100 g of the aversive mixture was consumed within a day's time. Con-sumption of the aversive mixture was measured on a daily basis and replenished accordingly. 6. Aversion was tested on a daily basis from day 2 onwards by challenging both the control sheep and the sheep continuously exposed to the aversive mixture for intake of the vermeerbos-maize meal mixture (1 :99 by mass). This was achieved by presenting 100 g of the vermeer-bos-maize meal mixture in the cleansed feed-ing-trough (the same trough in which the ver-meerbos-maize meal mixture was presented on day 0) each morning and determining the amount ingested after 1 h. Total intake of the mixture was arbitrarily taken as criterion that aversion was broken. 7. The aversive mixtures in replications 1, 2 and 3 were withdrawn on days 21, 36 and 103, re-spectively, which is at least twice the time that aversion in the corresponding control animals lasted. 8. Daily presentation of the vermeerbos-maize meal mixture to both the control sheep and the sheep exposed to the aversive mixture of repli-cations 2 and 3 was continued after withdrawal of the aversive mixture until totally consumed by the sheep exposed to the aversive mixture. Presentation of the vermeerbos-maize meal mixture to the control sheep of replication 1 was stopped after total consumption on day 3. The effect of continuous exposure to an aversive mixture on the duration of aversion in sheep of repli-cations 1, 2 and 3 is shown in Table 1. L.D. SNYMAN et al. The results indicate that aversion to the vermeer-bos-maize meal mixture in sheep continuously exposed to the aversive mixture lasted for at least as long as the sheep were exposed to the aversive mixture, although it was noticed that sheep of repli-cations 2 and 3 started to eat some of the ver-meerbos-maize meal mixture before removal of the aversive mixture. This presumably happened due to social facilitation by the control sheep after start-ing to eat their vermeerbos-maize meal mixture. Aversion was abolished within days after removal of the aversive mixture as indicated by total con-sumption of the vermeerbos-maize meal mixture. Aversion in the corresponding control sheep, on the contrary, only lasted for some time. Aversion of these sheep in replications 2 and 3 might have been prolonged due to the social influence of the sheep exposed to the aversive mixture. The overall results indicate that continuous exposure to the aversive mixture resulted in persistent aversion to the vermeerbos-maize meal mixture, despite the social influence of the control sheep. Lithium chloride ingestion (as a consequence of consumption of the aversive mixture) by the sheep exposed to the aversive mixture in replication 3 is shown in Fig. 3. The histogram in Fig. 3 shows a large fluctuation in daily LiCI ingestion due to vary-ing consumption of the aversive mixture. The learned-safety status and palatability of the maize meal in the aversive mixture tempted the sheep to consume the aversive mixture on a daily basis. Over-ingestion, which regularly took place, resulted in an increased adverse effect with diminished intake thereafter. Hereby the negative association formed with the taste of vermeerbos on day 0 was continuously reinforced, preventing intake of the vermeerbos-maize meal mixture presented in the same feeding-trough as during aversion treatment on day o. TABLE 1 Duration of aversion to a vermeerbos-maize meal mixture (1 :99 by mass) in sheep after an initial conditioning with LiCI (Control) and in sheep initially conditioned with LiCI followed by continuous exposure to an aversive mixture Replication 1 Replication 2 Replication 3 Measurements Control Aversive Control Aversive Control Aversive mixture mixture mixture Duration of exposure to the 0 21 0 36 0 103 aversive mixture (days) Day on which the vermeerbos- 3 28 11 37 51 108 maize meal mixture was totally consumed Mean lithium chloride ingestion 0 9 0 28 0 19 (mg/kg BM/day) 323 Maintaining aversion to vermeerbos (Geigeria ornativa O. Hoffm.) in sheep 120.--------------------------------------------------------------------------, >: 100 ns ~ a:I Cl -a, 80 .s I: o :; ~ 60 ---------- ---- --- ----Cl .= ~ :2 .2 .s::: 40 - - - - - - - - - - - - --() E .:! £: ::i 20 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 96 101 106 Days FIG. 3 Daily lithium chloride ingestion by the sheep continuously exposed to the aversive mixture in replication 3 The challenge for staying averted to the vermeer-bos-maize meal mixture was extremely high as 99% of the mixture consisted of maize meal. Main-taining aversion to this mixture for the periods investigated show that the technique of continuous exposure to an aversive mixture in principle was working and therefore might be usable in maintain-ing aversion to the less palatable vermeerbos on a pasture. Effect of continuous exposure to an aversive mixture on maintaining aversion to a pure stand of established vermeerbos Three averted sheep continuously exposed to an aversive mixture were tested for grazing vermeer-bos under the social influence of three non-averted control sheep grazing vermeerbos on an adjacent site. Two replications performed in two different years were conducted. A pure stand of established vermeerbos (22 m x 6 m in extent) was fenced off and longitudinally parti-tioned into two halves. A 2 m x 3 m area at the same end of each of the partitioned plots, cleansed of vermeerbos, was partitioned from the rest of the pasture by movable frameworks. The frameworks were such that sheep could put their heads through 324 the railings and graze a half metre strip of the ver-meerbos on the other side. On day 0, two groups of three sheep each were randomly allocated to each of the 2 m x 3 m partitions. The sheep were allowed to graze the vermeerbos growing within the half metre strip on the other side of the frameworks, which took them 6 h. One of the groups was then assigned to aversion treatment and each of the sheep in this group dosed with LiCI (160 mg/kg via stomach tube) plus 3 g sodium chloride (NaCI), dis-solved in a warm water extract prepared from 33 g fresh vermeerbos. Sodium chloride, known to the sheep, was given in an attempt to confuse the ani-mals with the taste of LiCI. From day 2 onwards, the treated group that had been made accustomed to maize meal before the time was continuously exposed to an aversive mix-ture, consisting of an aversive concentrate (5 g LiCI, 1 g NaCI and a hexane extract prepared from 15 g fresh vermeerbos) mixed with 94 g maize meal. The aversive mixture presented on day 2 contained only a quarter of the above-mentioned aversive concentrate , but was gradually increased over a 10-day period to contain the full amount on day 12. The sheep of both groups were tested for vermeer-bos intake from day 4 onwards by moving the frame-works half a metre further each morning, provided FIG. 4 Averted (left) and non-averted (right) sheep at the start of the trial (day 4) FIG. 5 Averted (right) and non-averted (left) sheep at the end of the trial (day 46) FIG. 6 Averted (at the back, not grazing) and non-averted (in front, grazing vermeerbos) sheep exposed simultane-ously to the same vermeerbos grazing that all accessible vermeerbos plants within the 0.5 m strip on the other side of the framework had been grazed down. Consumption of the aversive mixture was measured and replenished on a daily basis. Both groups received Eragrostis curvula hay and water ad lib. LD. SNYMAN et al. The averted sheep completely avoided vermeerbos when exposed to the vermeerbos on day 4, but was avidly grazed by the control sheep (Fig. 4). After 42 days (day 46) all the vermeerbos on the control's site had been grazed down while the averted sheep still stood at the starting point, with their framework not having been moved once (Fig. 5). They refused to graze vermeerbos despite the social influence of the control sheep grazing vermeerbos on the site next to them. Mean daily LiCI ingestion due to con-sumption of the aversive mixture by the averted sheep was 11.4 mg/kg BM/day. A replicate of this trial conducted in the following year yielded similar results. In this trial averted and non-averted control sheep additionally were placed together on the same vermeerbos site (site of the averted sheep) for an hour a day during the last six days of the trial, which lasted 49 days. Despite the increased social pressure they were subjected to, the averted sheep persistently refused to eat ver-meerbos (Fig. 6). The mean daily LiCI ingestion as a consequence of aversive mixture consumption by the averted sheep was 20.9 mg/kg BM/day. CONCLUSION The results of this study indicate that continuous exposure to an aversive mixture accomplished per-sistent aversion to vermeerbos under the circum-stances investigated, despite the social influence of non-averted control sheep. REFERENCES KELLERMAN , T.S. , COETZER, JAW. & NAUDE, T.w. 1988. Plant poisonings and Mycotoxicoses of Livestock in Southern Africa. Cape Town: Oxford University Press. KELLERMAN , T.S. , NAUDE, T.w. & FOURIE, N. 1996. The dis-tribution, diagnoses and estimated economic impact of plant poisonings and mycotoxicoses in South Africa. Onderste-poort Journal of Veterinary Research, 63:65-90. PROVENZA, F.D. & BURRITT, E.A. 1991. Socially induced diet preference ameliorates conditioned food aversion in lambs. Applied Animal Behavioral Science, 31 :229-236. RALPHS, M.H. & OLSEN, J.D. 1990. Adverse influence of social facilitation and learning context in training cattle to avoid eat-ing larkspur. Journal of Animal Science, 68:1944-1952. RALPHS, M.H. 1997. Persistence of aversions to larkspur in naIve and native cattle. Journal of Range Management, 50: 367-370. RALPHS, M.H., PROVENZA, FD., PFISTER, J.A., GRAHAM, D., DUFF, G.C. & GREATHOUSE, G. 2001 . Conditioned food aversion: from theory to practice . Rangelands, 23:14-18. STEYN, D.G. 1949. Vergiftiging van mens en dier. Pretoria: J.L. van Schaik Beperk. 325 

Continuous exposure to an aversive mixture as a means of maintaining aversion to vermeerbos (Geigeria ornativa O. Hoffm.) in the presence of non-averted sheep

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Continuous exposure to an aversive mixture as a means of maintaining aversion to vermeerbos (Geigeria ornativa O. Hoffm.) in the presence of non-averted sheep

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