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This article was downloaded by: [Nipissing University]On: 08 October 2014, At: 09:57Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,UK
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The effects of grazing sheep onmocap-treated pastureS.R.B. Solly aa Wallaceville Animal Research Centre , Departmentof Agriculture , Private Bag, Wellington , NewZealandPublished online: 06 Feb 2012.
To cite this article: S.R.B. Solly (1972) The effects of grazing sheep on mocap-treated pasture, New Zealand Journal of Agricultural Research, 15:1, 83-90, DOI:10.1080/00288233.1972.10421281
To link to this article: http://dx.doi.org/10.1080/00288233.1972.10421281
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83
THE EFFECTS OF GRAZING SHEEPON MOCAP~REATED PASTURE
By S. R. B. SOLLv-
(Received 3 September 1971)
ABSTRACT
Pastures were topdressed with pellets of 5% Mocap at ratesequivalent to 2.24 kg and 4.48 kg active ingredient (a.i.) per hectare.Residues of Mocap on the treated pasture disappeared rapidly, fallingto approximately 2 parts per million (ppm) on a dry-matter basis forboth rates 15 days after topdressing.
In a second trial, pastures were topdressed with pellets of 10%Mocap at the rate of 2.24 kg a.i.(ha, and sheep were grazed on themafter withholding periods of 0, 3, 7, and 14 days. None of the animalsshowed ill effects, although erythrocyte cholinesterase activity wasreduced in most of them. Samples of omental fat taken from sheepthat had grazed topdressed pasture for 6 days contained no detectableresidues « 0.01 ppm) of Mocap.
INTRODUCTION
Mocap (O-ethyl S,S,-dipropylphosphorodithioate) is an effectiveorganophosphate for control of grass grub (Costelytra zealandica White)in pasture (Raaijen 1969; Taylor 1970; Read 1970; Fenemore 1970).
DuVal and Boyd (1967) report half-lives for this insecticide insoils ranging from 3-9 days for applications of 1.12 kg a.i.zha (1 lba.i./acre) and 4--12 days for applications of 2.24 kg a.i.rha, Althoughthis relatively short persistence in soil might be expected to reduce itseffectiveness as a soil pesticide, Mocap is soluble in water to the extentof 750 ppm (Anon. 1969), which should give some mobility in soil.Mocap applied as a surface dressing may, therefore, penetrate the soiland reach the target organism more rapidly than other, less water-solublepesticides.
To the author's knowledge there are no reports in the literatureon the persistence of Mocap residues under New Zealand conditions.However, reports of work from other sources suggest that under recommended conditions of use, residues on treated pasture would disappearrapidly, and residues in stock grazing these pastures would be negligible.For example, Mocap residues have not been found in many cropsgrown in Mocap-treated soil (Anon. 1969), and soil application of
* Wallaceville Animal Research Centre, Department of Agriculture, Private Bag,Wellington. New Zealand.
N.Z. Journal of Agricultural Research (1972), 15: 83-90
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84 Sheep on Mocap-treated pasture
Mocap at the exaggerated rate of 50 ppm resulted in Mocap restdueswhich reached a maximum value of only 2 ppm in corn grown in thetreated soil for 2 weeks (Boyd 1968).
Menzer (1967) has shown that Mocap is rapidly broken down incorn seedlings, and he suggested that the first step in the catabolism ofMocap by these plants is the hydrolysis of one of the S-propyl groupsto form propyl mercaptan and a thiolophosphoric acid. If this is themajor catabolic pathway, it is unlikely that toxic products would beformed in plants, and only the parent compound would be of interestin regard to toxicology of residues in treated plants.
The toxicity of Mocap to sheep and calves has been examined bySchlinke (1969), who found that a sheep dosed orally with Mocap atthe rate of 50 mg a.i./kg body weight was poisoned, but recoveredafter therapy. Other sheep dosed at rates of 25 and 10 mg a.i.ykg bodyweight showed only slight or no effects, although their whole-bloodcholinesterase activities were reduced. Calves were more susceptiblethan sheep.
The short persistence of Mocap in soil and in crops and the availabledata on its toxicity suggested that its use for controlling pasture pestsin New Zealand should present little hazard to grazing animals, provideda suitable withholding period was observed.
The experiments reported in this paper were performed to determinethe effects of grazing sheep on Mocap-treated pasture after variouswithholding periods.
EXPERIMENTAL
Trial 1: The persistence of Mocap on pasture
The experimental site for this trial was at Springvale Road,Wanganui. The soil type was a yellow-brown sand (Anon. 1968).
A permanent pasture composed of perennial ryegrass (Loliumperenne L.), browntop (Agrostis tenuis Sibth.), catsear (Hypochaerisradicata L.), and white clover (Trifolium repens L.) was topdressedwith 5% Mocap granules using a spinner distributor attached to amotor-car. The car was driven at constant speed across the paddockto give three topdressed strips, each approximately 6 m wide X 90 mlong. Two of the strips were treated at the rate of 2.24 kg a.i.rha,and the third at 4.48 kg a.i./ha. At the time of topdressing (22 July1970), the pasture was 3-10 cm long, and dry, but the soil was very wet.
Trial 2: The effects of grazing sheep on pasture topdressed with Mocap
At Wallaceville four 0.1 ha paddocks of established pasture(numbered 2-5), predominantly a mixture of L. perenne and T. repens,were topdressed with 10% Mocap granules at a rate of 2.24 kg a.i.yha.Topdressing was by hand, on 4 November 1970, when the pasture wasdry and short (3-8 ern). A fifth 0.1 ha paddock (No.1) was leftuntreated to serve as a control. During the night after topdressing3.8 mm of rain was recorded.
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S. R. B. SOLLY 85
Paddocks 2-5 were grazed by separate groups of four Romney!Southdown cross-bred ewe hoggets, aged 14 months and approximately40 kg body weight, after withholding periods of 0, 3, 7, and 14 daysrespectively. A fifth group of four sheep was grazed on the untreatedcontrol paddock (No.1) concurrently with the O-day group. All sheepwere grazed on the trial paddocks until 28 days after topdressing. Theanimals were weighed 2 days before, and 6, 13, 20, and 28 days aftertopdressing.
Sampling procedures
Blood-To establish pre-trial erythrocyte cholinesterase activitiesblood was sampled from the jugular vein of each sheep on two separatedays before the animal was exposed to Mocap. Further samples ofblood were taken at intervals during the trial. Heparin was used asanti-coagulant.
Fat-Samples of omental fat were removed from all sheep 14 daysbefore the start of the trial. Subsequently a sample of omental fat wastaken from each sheep 6 days after it had been put on to topdressedpasture. Samples of omental fat were also taken from sheep in the controland O-day groups 20 days after they had been put on to treatedpasture.
Pasture-Pastures were sampled, stored, and sub-sampled foranalysis as described by Solly et al. (1971).
In Trial 1 it was not possible to obtain pre-treatment pasturesamples, but a "control" sample was taken from pasture near thetreated strips at the time of the first post-treatment sampling, 8 daysafter topdressing. Other samples were taken from the topdressed areas15 and 29 days after topdressing.
In Trial 2 one composite pre-treatment sample was taken from allplots immediately before topdressing. Individual samples were takenfrom each plot immediately after topdressing, and 3, 7, 14, 12, and 28days after topdressing.
Mocap granules-To test the rate of leaching of Mocap fromgranules used in the Wallaceville trial, samples of granules were collectedfrom thistle leaves in paddocks 4 and 5 at 2, 3, 5, and 7 days aftertopd ressinr;
Analytical
Blood-Erythrocyte cholinesterase activity was determined electrometrically (Michel 1949). Results are expressed as percentages of themean of the pre-trial t. pH values.
Sheep fat-Five grams of fat were macerated with 10 g anhydroussodium sulphate and 50 ml hexane in a top-drive macerator. Thesupernatant liquid was decanted through a glass wool plug into aseparating funnel, the insoluble residue was extracted twice more with25 ml lots of hexane, and the extracts were filtered as before. Thecombined filtrates were partitioned into acetonitrile (Solly and Harrison1971), the acetonitrile extract evaporated, and the residue taken upin 0.5 ml hexane. Approximately 5 ,ttl of the hexane solution wasinjected into the gas chromatograph.
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86 Sheep on Mocap-treated pasture
Recoveries of Mocap from control samples of fat fortified at levelsof 1.0 ppm and 0.1 ppm were 93% and 81% respectively.
Results are expressed as ppm Mocap on a raw fat basis. Nocorrection was made for recoveries.
The limit of sensitivity of the method was 0.01 ppm.
Pasture-Twenty-five-gram sub-samples of pasture were maceratedfor 2 minutes in a top-drive macerator with 150 ml ethyl acetate, 10 gCelite 545 was added, and the mixture was stirred and filtered throughWhatman No. 1 filter paper on a Buchner funnel. The residue on thefilter paper was pressed down with a spatula and washed with three25 ml portions of ethyl acetate. The combined filtrates were pouredthrough approximately 5 g anhydrous sodium sulphate in a filterfunnel, and the sodium sulphate washed with a further small volume(approximately 10 ml) of ethyl acetate. The volume of the combinedfiltrates was measured, and an aliquot equivalent to 10 g pasture wasevaporated to a volume of approximately 5 ml under reduced pressurein a rotary vacuum evaporator. The residue in the evaporator flaskwas quantitatively transferred to a stoppered graduated test tube, andthe volume made to 10 ml with ethyl acetate. One gram Norit A(Baetz 1964) was added to the liquid in the tube, and the tube wasshaken, centrifuged for approximately 2 minutes at 1,000 rpm, a 5 mlaliquot of the supernatant liquid was removed, and the volume adjustedwith ethyl acetate to give a suitable concentration of Mocap (approximately O.lfLg/ml or 1.0 fLg/ml) for gas chromatography.
All pasture samples were analysed in duplicate.
The mean recovery of Mocap from control pasture samples fortifiedat a level of 1.0 ppm was 84%. Results have not been corrected forthe recovery.
Results are expressed as ppm Mocap on a dry-matter basis. Thelimit of sensitivity of the method was 0.1 ppm.
Granules-Approximately 100 mg granules were accurately weighedinto a 5 ml volumetric flask and the flask filled to the mark with ethylacetate. The flask was stoppered, shaken vigorously for 1 minute, andallowed to stand overnight in the dark at room temperature. Thefollowing day the mixture was again shaken, allowed to settle, andanalysed with the gas chromatograph.
Gas chromatography-Extracts were analysed using a Pye Panchromatograph fitted with a thermionic detector. All-glass columnsmeasuring 1.5 m in length X 4 mm internal diameter were used withtwo types of packing:
(a) 4% w/w Reoplex 400 (Varian Aerograph Ltd, Walnut Creek,California, U.S.A.) on Diatomite CQ 100/120 mesh (PyeUnicam, Cambridge, England), maintained at a temperatureof 183°c.
(b) 3% w/w DC-200 (Varian Aerograph Ltd) on Diatomite CQ100/120 mesh at a temperature of 200°c.
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S. R. B. SOLLY 87
3025
0 ...... ·0 CONTROL GROUPcoO-DAY GROUP€ ~ 3-DAY GROUP.'J o!. 7-DAY GROUP~ 14-DAY GROUP
5
>- 1201I-:> 100-i=:u-< 80.....VI-eQt:
60......I-en......:z:
40:::;0::J:U
z 20-<u..~ 0
0 10 15 20
DAYS AFTER TOPDRESSINGFig. l-e-Mcan erythrocyte cholinesterase activities (pre-trial activity 100)
of groups of sheep on Mocap-treated pasture.Each point is the average value for four sheep.
... sheep put on to trial pasture.Key:
... sheep removed from trial pasture.
Oxygen-free nitrogen was used as carrier gas, with a flow rate or30 ml/min through the detector in both cases.
On column (a) the retention time of Mocap was 3 minutes and oncolumn (b) it was 2 minutes. Quantitative analyses were based onpeak height comparisons with appropriate standards.
RESULTS
Omental fat-All omental fat samples were analysed. Using the3% DC-200 gas chromatograph column the reagents used in thisanalysis gave a peak which coincided with Mocap and which wasequivalent to a level of approximately 0.01 ppm. However, re-analysisof the extracts on the 4% Reoplex 400 column resolved this "blank"from the Mocap peak, and all fat samples were found to contain lessthan O.oI ppm Mocap.
Pasture-Pasture residues for the Wanganui and WaIlaceviIle trialsare shown in Tables I and 2 respectively. All pasture extracts wereanalysed using the 3% DC-200 gas chromatograph column, and oneset of duplicate samples from the WaIlacevilIe trial was re-analysed onthe 4% Reoplex 400 column. There was good agreement betweenresults obtained using the two different column packings.
Blood-Sheep erythrocyte cholinesterase levels are shown in Fig I.
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88 Sheep on Mocap-treated pasture
TABLE l~Wanganui Trial: Residues oi Mocap on Pasture after Topdressing(ppm dry-matter basis)
Days after topdressing
Strip Treatment(kg a.i.rha)
8 15 29
Control 0 < 0.1
North 2.24 8.2 3.6 0.5
Centre 2.24 6.3 1.7 0.4
South 4.48 16.0 1.7 0.5
Cumulative rainfall (mm)* 15.5 35.8 77.1
* Recorded 1t miles west of trial site.~ Indicates that no sample was taken.
TABLE 2~Wallaceville Trial : Residues of Mocap (ppm dry-mater basis) onPasture after Topdressing
Days after topdressingPaddock Withholding
no. period (days)Treatment(kg a.i.rha)
o 3 7 14 21 28
1
2
3
4
5
oo3
7
14
o (control)
2.24
2.24
2.24
2.24
6.4*
152.0*
74.0
111.0
102.0
37.2*
0.6
12.8
11.4
8.6*
5.6
<0.1
0.6
0.6
0.5
1.4*
<0.1
0.2
0.2
0.2
0.2
<0.1
0.2
0.1
0.1
0.1
Cumulative rainfall (mm) o 4.6 4.6 5.6 5.8 5.8
* Denotes the level of Mocap on pasture immediately before sheep wereintroduced to the paddock.
~ Indicates that no sample was taken.
TABLE 3~Wallacevil1c Trial: Residues of Mocap III Granules Broadcast onPasture
Days after % Mocap inCumulative rainfall (mm)topdressing granule
Ot 9.80 0
2 0.17 4.6
3 0.33 4.6
5 0.17 4.6
7 0.03 *4.6-----
* A trace ('::: 0.1 mm) of rain fell during the 6th day after topdressing.t Nominally 10% Mocap.
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S. R. B. SOLLY 89
Granules--Residues of Mocap in granules used in the Wallacevilletrial are shown in Table 3.
Sheep weights-There was no significant variation between thegrowth rate of sheep in the treated groups and those in the controlgroup.
DISCUSSION
Pasture residues-The mean level of residues found in theWallaceville trial 7 days after topdressing was 9.6 ppm, compared with7.3 ppm for the 2.24 kg a.i.yha treatments at Wanganui 8 days aftertopdressing. Subsequently Mocap residues tended to be slightly morepersistent in the Wanganui pasture than at Wallaceville, in spite ofthe greater rainfall at Wanganui (Tables 1 and 2). The rate of lossof Mocap from the granules broadcast at Wallaceville was initiallyvery rapid (Table 3), probably because 4.6 mm of rain fell duringthe night and day after topdressing. From 2-5 days after topdressingno further loss of Mocap from the granules occurred, but betweenday 5 and day 7 after topdressing there was a further loss of Mocapfrom the granules, possibly due to a trace of rain « 0.1 mm) that fellduring the 6th day after topdressing.
Efjects on sheep-In spite of the comparatively high levels of Mocapon pasture at the time the O-day group began grazing (Table 2,paddock No.2), the only clinical symptom of organophosphate poisoningdetected in this group was slight scouring after 5 days.
Assuming that a sheep eats 1 kg dry matter per day, the approximateintake of Mocap by sheep in the O-day group during the first day ontopdressed pasture would have been 150 mg (taking the level of Mocapon the pasture throughout the day as 150 ppm). For a 40 kg sheepthis would represent a maximum exposure of 3.75 mg/kg body weight/day, well below the maximum safe dose of 10 mg/kg body weight foundby Schlinke (1969) in acute oral toxicity studies with Mocap in sheep.Obviously the rate of intake of Mocap would decrease as the pastureresidues were dissipated during subsequent days.
Blood cholinesterase levels were significantly depressed (P < 0.05)in both the O-day and the 3·day groups of sheep, reaching a meanminimum value of 38% of the pre-trial levels in both groups after theyhad been on topdressed pasture for 13 days and 10 days respectively(Fig. 1). This slow persistent fall in enzyme activity is difficult toreconcile with the rapid disappearance of Mocap froq,. pasture (Table 2)and with the absence of Mocap from omental fat of sheep. It is, ofcourse, possible that Mocap is stored in some tissue other than fat,and slowly released from this reservoir into the blood. However, dosingtrials in which dogs were administered 21 consecutive daily oral dosesof Mocap at rates up to 0.0625 mg a.i.Zkg body weight/day indicatedthat Mocap was not stored in the blood, muscle, kidney, liver, or fatof these animals (Hosling 1968).
Results of the trial reported here and of the feeding trial withdogs (loc. cit.) do not entirely eliminate the possibility that Mocap
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90 Sheep on Mocap-treated pasture
is stored in some sheep tissues, although from the data so far availablethis seems unlikely. Therefore, until further work is done on thedistribution of Mocap in sheep, it is impossible to specify with certaintya withholding period that will ensure residue-free products derived fromanimals grazing pastures topdressed with Mocap.
The trials reported here indicate that a minimum withholding periodof 7 days after topdressing with 10% Mocap granules at a rateequivalent to 2.24 kg a.i.rha would be sufficient to avoid hazards oftoxicity to sheep.
AcknowledgmentsMr R. L. Taylor, Farm Chemicals Co. Ltd, Port Mapua, for topdressing
the pasture at Wanganui and for arranging the supply of Mocap granules;Mr R. Ness, Mobil Oil New Zealand Ltd, for sampling pasture in the WanganuiMr K. S. Heppleston and Miss V. Shanks, Wallaceville, for technical assistance;trial.
REFERENCESANONYMOUS 1968: N.Z. Soil Bureau 1968: Soils of New Zealand Part 1.
N.Z. Soil Bureau Bulletin 26: (l).ANONYMOUS 1969: Mocap (V-C 9-104) (Ent. 27,318). Technical
Bulletin No. 5 (March 1969). Mobil Chemical Co., Virginia,U.S.A. 2 pp.
BAETZ, R. A. 1964: Norit A clean-up for chlorinated pesticide analysisby micro-coulometric gas chromatography. Journal of theAssociation of Official Agricultural Chemists 47: 322-5.
BOYD, G. R. 1968: Residues of Mocap in corn plants treated atexaggerated rates. Technical Report on Project 532. MobilChemical Co., Virginia, U.S.A. 5 pp.
DUVAL, AUDREY F.; BOYD, G. R. 1967: The persistence of Mocap Intreated soil. Technical Bulletin R N 67-3. Mobil Chemical Co.,Virginia, U.S.A. 9 pp.
FENEMORE, P. G. 1970: Field trials against grass grub including somenewer insecticides. Proceedings of the 23rd N.Z. Weed and PestControl Conference: 172-6.
HOSLlNG, G. C. 1968: Residue study in dogs with Mocap, TechnicalReport, August 16, 1968. Mobil Chemical Co., Virginia, U.S.A.
MENZER, R. E. 1967: Uptake and metabolism of Mocap by plants.Technical Report. Mobil Chemical Co., Virginia, U.S.A. 22 pp.
MICHEL, H. O. 1949: An electrometric method for the determination ofred blood cell and plasma cholinesterase activity. Journal ofLaboratory and Clinical Medicine 34: 1564-8.
RAAIJEN, P. H. 1969: Chemical control of grass grub. Results 01 malwork during 1967-8 season. Proceedings of the 22nd N .~. Weedand Pest Control Conference: 253-7.
READ, P. E. C. 1970: Grass grub control by chemicals 196'.1: Proceedingsof the 23rd N.Z. Weed and Pest Control Conference: 169-71.
ScHLINKE, J. C. 1969: Toxicological effects of five soil nematocides incattle and sheep. Journal of the American Veterinary and MedicalAssociation 155, 1364-6.
SOl.LY, S. R. B.; HARRISON, D. L. 1971: Fensultorruon I: Toxicity tosheep and rats, residues in sheep, and persistence on pasture.N.Z. Weed and Pest Control Conference: 159-62.
SoLLY, S. R. B.; HARRISON, D. L.; HUNNEGO, J. N.; SHANKS, V. 1971:Fensulfothion II: The effects of grazing sheep on fensulfothiontreated pasture or on pasture grown in fensulfothion-treatedsoil. Ibid: 79--87.
TAYLOR, R. L. 1970: Control of grass grub. Proceedings of the 23rdN.Z. Journal of Agricultural Research 14: 66-78.
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