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Efficacy of Four Dichlorvos Formulations Against Adult Hyostrongylus Rubidus and Oesophagostomum Spp. in Pigs
Br. vet.
J.
(1973), 129, xxi
SHORT COMMUNICATIONS
EFFICACY OF FOUR DICHLORVOS FORMULATIONS AGAINST ADULT HYOSTRONGYLUS RUB/DUS AND OESOPHAGOSTOMUM SPP. IN PIGS L.
F.
TAFFS,*
I. J. LEAN,t D. E. M. K. CURRANt
JACOBS** AND
·Royal Veterinary College, Potters Bar, Herts; tWye College, Nr. Ashford, Kent; and • • Shell Research Limited, Tunstall Laboratory, Sittingbourne, Kent
SUMMARY
The anthelmintic action of four formulations of dichlorvos against adult Hyostrongylus rubidus and Oesophagostomum spp. was evaluated in a controlled test using 25 artificially-infected pigs. The activity of the newer V I 3 (96. I per cent efficient), PFI 18 (96.6 per cent efficient) and V 22 (99'9 per cent efficient) formulations against Hyostrongylus compared favourably with the original V 3 product (99.6 per cent efficient) when given individually at oral dose rates of 35, 35, 13 and 35 mg active material per kg bodyweight respectively. Efficiencies of 100 per cent (VI3), 98'7 per cent (PFII8), 100 per cent (V22) and roo per cent (V3) were obtained against Oesophagostomum; these results were, however, equivocal as the worm burdens of all the infected, untreated controls were low. In a second experiment using 12 naturally-infected sows, both the V 22 and V3 formulations reduced "strongyle" faecal egg counts to zero seven days after treatment. INTRODUCTION
The V3 formulation of the broad spectrum anthelmintic dichlorvost (0, 0dimethyl 1-2, 2-dichlorovinyl phosphate) has been shown to have high activity against Hyostrongylus rubidus and Oesophagostomum spp. in pigs (Jacobs, 1968; Forstner & Matzke, 1969; Taffs, 1969; Jacobs, Taffs, Lean & Curran, 1970; Jacobs, Curran & Taffs, 1971). The purpose of this work was to compare the action of four different formulations of dichlorvos against adult H. rubidus and Oesophagostomum spp. in artificially infected growing pigs. Also the effect of the newer V 22 formulation of dichlorvos is compared with that of the original V 3 formulation against naturally acquired "strongyle" infestations in adult pigs.
* Present
address: Medical Research Council, National Institute for Medical Research, Mill Hill, London,
N.W·7·
** Present address:
Department
shire.
:j: Atgard, a Shell trade-mark. V3-an extruded resin pellet formulation intended for application as a feed dressing; V 13-a coated version of the V 3 formulation designed for use in premix feedstuffs; V2 2-similar to V3 but different release rate characteristics allow a lower dose-rate to be effectively employed. PFI18-An experimental formulation for incorporation into pelleted feedstuffs.
xxii
BRITISH VETERINARY JOURNAL,
12 9,
3
MATERIALS AND METHODS
In Experiment I, 25 worm-free castrated Landrace pigs were stratified on the basis of body weight, then allotted at random to five groups of five pigs. Each group was housed separately in a pen with a concrete floor which was cleaned daily. The pigs were fed a balanced diet of pelle ted meal (16 per cent crude protein) once daily to a commercially acceptable feed scale. Animals were between 9-IO weeks of age when infected orally with 6000 Hyostrongylus and 24,000 Oesophagostomum spp. (0. dentatum and O. quadrispinutatum) infective third-stage larvae which had been collected from cultured faeces of experimentally infected pigs. Dichlorvos therapy was effected by mixing the appropriate quantity of the formulated product into the feed of each individual pig forty days after infection, as follows: Group I-VI3, 35 mg/kg; Group 2-PFII8, 35 mg/kg; Group 3-V3, 35 mg/kg; Group 4-V22, 13 mg/kg; Group 5 acted as an infected, untreated control. Faecal egg counts and cultures were carried out on days -8, 0 (the day of infection, 21, 33, 40, 43 and 47. Forty-seven days after infection, i.e. seven days after treatment, the pigs were killed. To aid worm counting, food was withheld for the last 24 hours. The methods of processing of the stomachs and large intestines for worms, which were collected, identified and individually counted, were similar to those described previously (Taffs, 1971). Anthelmintic activity was assessed by noting the effect of the different formulations on faecal egg counts and on cultures, and by comparing the worm burdens of the treated groups with those of the untreated control group (controlled test). In Experiment 2, worm eggs counts and faecal cultures were carried out on faecal samples taken at random from 25 adult pigs in a commercial herd. Twelve sows with the highest egg counts were chosen for the trial. Six sows were dosed with the newer V22 formulation and six others with the original V3 formulation of dichlorvos (see Table II). The anthelmintic was mixed with dry meal and given to pigs individually without water. Individual V22 doses were made up by dividing one sachet holding I 1·2 g total formulation, containing 20 per cent dichlorvos, into four equal portions. Individual V 3 doses consisted of one sachet containing 7·5 g total formulation. Faecal samples were collected on days - 12, 0 and + 7. Anthelmintic activity was assessed by comparing preand post-treatment faecal egg counts and cultures. In both experiments the methods of faecal egg counting (McMaster) and culturing were similar to those previously described (Taffs, 1971). A qualitative and a rough quantitative examination of third-stage larvae recovered from faecal cultures were made. RESULTS AND DISCUSSION
The results are presented in Tables I (Experiment I) and II (Experiment 2). As revealed by an examination of faecal egg counts and cultures, all the experimentally infected pigs except one (Pig NO.9) were shedding Hyostrongylus
TA B LE I
EX PERIM E N T
I. T H E A C TION OF FOUR DIFFE R ENT FOR MULAT I ONS OF D1 C H LO R VOS AG A INST ADULT E X PE RI MENTAL L Y I N F ECTE D P I GS
"Strongyle" faecal egg counts (eggs/g) Dichlorvos Weight at Days after infection f ormulation Group dose Pig treatNo. rate No. meet (kg) - 80 (mg/kg ) 21 40 43 47 33
H . rubidus and Oesophagostomum
SPP. I N
Parasites found post mortem (Day 47 ) Oesophagostomum spp.
Hyostrongylus Individual
Group Total
Average
Percentage efficiency
t>:1
'Tl
Group
Individual T otal
Average
Percentage efficiency
....'Tl 0
>
0
too<:
V I3 35
2
P F I18 35
3
V3 35
I 2 3 4 5
28 51 60 41 32
0 0 0 0 0
0 0 0 0 0
100 100 0 100 200
67 00 3 00 3 00 19 00 200
57 00 4 00 4 000 3 000 39 00
0 0 0 0 0
0 0 0 0 0
3 13 0 2 0 0
6 7 8 9 10
33 46 57 45 36
0 0 0 0 0
0 0 0 0 0
100 0 100 0 0
200 800 100 200 2200
3 00 1700 5 600 3 00 2 100
0 0 0 0 0
100 0 0 0 0
266 0 2 0 0
II
40 59 57 43 43
0 0 0 0 0
0 0 0 0 0
100 100 100 100 100
3900 1000 10 0 2000 3700
6400 6200 200 5 600 4 00
0 0 0 0 0
0 0 0 0 0
25 0
18 19 20
50 45 55 49 41
0 0 0 0 0
0 0 0 0 0
0 100 100 200 100
100 100 5 00 17 00 700
100 3 00 100 200 5900
0 0 0 0 0
0 0 0 0 0
0 0 2 2
21 22 23 24 25
55 50 49 42 40
0 0 0 0 0
0 0 0 0 0
100 100 100 100 100
100 1500 700 5 00 3700
3 00 65 00 200
0 100* 0 100 100
100 3 00 100 700 4 00*
12 13 14 15 16
4
5 Con trol
V22 13
Not t r eated
I7
200
1800
I
3 15
268
28
63
54
6
96 ' 1
9 6 .6
99 .6
2 0
18 93 1534 634 193 2 2 0 79
99 '9
5
80 7 2
161 4
H . Tubidus a nd 24,000 Oesophagostomum spp . larvae on Day o . Treatment was o n Day 40 . ... Oesophagostomum worms observed in faeces o n egg coun ting.
Pigs infec ted wi th 6000
0
0 0 0 0 0
0
0 0 7 0 I
8
0 0 0 0 0 0 0 0 0 0 40 70 4 27 0 0
0
100
'Tl 'Tl
0 C
~ t)
2
9 8 '7
.... 0 ::z:: t'"
0
~
<:
0
0
100
0
r:Jl
'Tl
0
~
0
0
100
s::C
S .... 0
Z
r:Jl
77 1
154
il ~:
TABLE II EXPERIMENT 2. THE EFFECT OF DICHLORVOS FORMULAT ION V22 ON "STRO NGYLE" FAECAL EGG COUNTS (EGGS/G FAECES) AND CULTURES IN ADULT PIGS COMPARED WITH THE ACTION OF THE V3 FORMULATION
II ~.
Day Sow No.
Dichlorvos formulation treatment
o Dosing
- 12
Culture Des.
V22
63 00
+++
76 0
3s00
+ + ++
99
2000
++ +
104
1600
+++
106
2000
+++
119 11 6
V3
Hyo. 800 + (10)
+ (1)
100
+
0
+ (1)
Hyo.
23 00
+++
0
+ (6)
0
+ (1)
+ (2)
600* 1200
++
1700
113
1000
+ +
100
102
70 0
+ (35)
:I:
<: >-l trl ::0 .....
~...::
t.-.
++
C
0
++ + (1)
0
+ + +
0
+++
0
+ (17)
~
>
t' ~
'"
~
<.>::>
1100
+ (50) ++ +
0 0
* Fall in egg count from Day - 12 is probably a reflection of effect of weaning on p eriparturient egg rise since these two pigs weaned their litters between days - 12 and o.
d enotes number of larvae recovered.
~ ..... >-l ..... rFJ
0
ISOO
** With litter . + to + + + +
II
trl
0 + (1)
6S
+ ++
+ (18)
0
1000
+++
0
++++
+++
2200
+ (5)
Des.
4800
3900
112
+++ + (46)
200
++++
Hyo.
100*
++
2300**
Egg count Des.
SOo
122
Culture
Egg count
Egg count
48
+ 7
Culture
EFFICACY OF FOUR DICHLORVOS FORMULATIONS
xxv
eggs in the faeces at least as early as the 2 I st day. All the Oesophagostomum infections except four (Pigs No. I I, 13,23,20) had become patent by that time. By the 33rd day all pigs were shedding both Hyostrongylus and Oesophagostomum eggs in the faeces. The medicated feed was eaten without hesitation. No side-effects were observed. Three and seven days post-treatment, the faecal egg counts of all the treated pigs except one (Pig No.6) were reduced to zero. A fall in egg counts was also noted in two (Pigs No. 22, 25) of the controls and Oesophagostomum worms were observed in the faeces of both animals on the 43rd (Pig No. 22) and 47th (Pig No. 25) days during egg counting. From the recovery of Hyostrongylus worms post mortem the activities of the V 13, PF I 18 and V 22 formulations of dichlorvos compared very favourably (96'1,96.6,99'9 per cent effective) with that of the V 3 formulation (99.6 per cent effective). A similarly high activity (99'4 per cent) of the latter commercial product against adult Hyostrongylus was observed in previous work (Jacobs et al. 1970). Efficacy values of roo, 98'7, 100 and roo per cent were recorded against Oesophagostomum for the VI3, PFII8, V3 and V22 formulations respectively. These results must, however, be interpreted with caution as although only eight worms were recovered from the 15 treated pigs, no worms were found in two of the controls (Pigs No. 24, 25). The egg-count and culture data showed that good "takes" were achieved and that a rapid drop occurred inthe control pigs after the 40th day. Although it is conceivable that these data reflect a natural expulsion of adult worms occurring at that time, the possibility that the control pigs may have ingested faeces containing dichlorvos pellets originating from the treated animals and transmitted via the common clearing passage could not be totally excluded. In Experiment 2, the two formulations of dichlorvos were eaten with the dry meal quite readily and full doses were consumed. Prior to dosing, all the pigs were naturally infected with Oesophagostomum and three (Sows No. 760, 106, 122) were also infected with Hyostrongylus. Seven days after dosing the "strongyle" egg counts were reduced to zero in all 12 pigs. Only one culture (Sow No. 122) was positive in the group treated with the V3 formulation. This indicated that the commercial formulation was almost roo per cent effective against adult Oesophagostomum, and this is in agreement with the results obtained in Experiment I and previously (Jacobs, 1968; Forstner & Matzke, 1969; Taffs, 1969; Jacobs et al., 1971). An examination of faecal cultures from the V22 dosed group seven days after treatment revealed the probably complete clearance of worms from one pig (Sow No. 99). The results of the other five indicated that only a few Oesophagostomum worms remained after dosing. No Hyostrongylus worms were recovered in culture from the three infected pigs after dosing with either formulation. This confirms the high activity shown against Hyostrongylus by both formulations in Experiment I and the V3 formulation in previous work (Forstner & Matzke, 1969; Jacobs et al., 1970). It is unlikely that the fall in egg count was indicative of only a suppression of egg production since actual expulsion of both genera of worms followed treatment in Experiment I.
xxvi
BRITISH VETERINARY JOURNAL, 129,3
This work has shown that the newer VIg, PFII8, and V22 formulations of dichlorvos are as efficient, or very nearly as efficient, as the original V g formulation in expelling adult Hyostronglus from pigs. The results also indicate, although not unequivocally so, since few worms were found in the controls, that the VIg, PFII8 and V22 formulations are as effective, or nearly as effective, as the V g product in removing Oesophagostomum. ACKNOWLEDGEMENTS
The authors thank Dr A. J. Probert for the supply of infective H. rubidus larvae, and Professors J. A. Laing and J. L. Hancock for providing laboratory facilities for one of us (L.F.T.). REFERENCES FORSTNER, M.j. & MATZKE, P. (196g). Dt. tieriirztl. Wschr. 76, 283. JACOBS, D. E. (1968). Vet. Rec. 83, 160. JACOBS, D. E., CURRAN, M. F. & TAFFS, L. F. (1971). Res. vet. Sci. 12, JACOBS, D. E., TAFFS, L. F ., LEAN, I. j. & CURRAN, M . F. (1970). Br. TAFFS, L. F. (1969). Vet. Rec. 85, 166. TAFFS, L. F. (1971). Vet. Rec. 165'
ag,
189. vet.
J.
126,
xliii.
J.
(1973), 129, xxi
SHORT COMMUNICATIONS
EFFICACY OF FOUR DICHLORVOS FORMULATIONS AGAINST ADULT HYOSTRONGYLUS RUB/DUS AND OESOPHAGOSTOMUM SPP. IN PIGS L.
F.
TAFFS,*
I. J. LEAN,t D. E. M. K. CURRANt
JACOBS** AND
·Royal Veterinary College, Potters Bar, Herts; tWye College, Nr. Ashford, Kent; and • • Shell Research Limited, Tunstall Laboratory, Sittingbourne, Kent
SUMMARY
The anthelmintic action of four formulations of dichlorvos against adult Hyostrongylus rubidus and Oesophagostomum spp. was evaluated in a controlled test using 25 artificially-infected pigs. The activity of the newer V I 3 (96. I per cent efficient), PFI 18 (96.6 per cent efficient) and V 22 (99'9 per cent efficient) formulations against Hyostrongylus compared favourably with the original V 3 product (99.6 per cent efficient) when given individually at oral dose rates of 35, 35, 13 and 35 mg active material per kg bodyweight respectively. Efficiencies of 100 per cent (VI3), 98'7 per cent (PFII8), 100 per cent (V22) and roo per cent (V3) were obtained against Oesophagostomum; these results were, however, equivocal as the worm burdens of all the infected, untreated controls were low. In a second experiment using 12 naturally-infected sows, both the V 22 and V3 formulations reduced "strongyle" faecal egg counts to zero seven days after treatment. INTRODUCTION
The V3 formulation of the broad spectrum anthelmintic dichlorvost (0, 0dimethyl 1-2, 2-dichlorovinyl phosphate) has been shown to have high activity against Hyostrongylus rubidus and Oesophagostomum spp. in pigs (Jacobs, 1968; Forstner & Matzke, 1969; Taffs, 1969; Jacobs, Taffs, Lean & Curran, 1970; Jacobs, Curran & Taffs, 1971). The purpose of this work was to compare the action of four different formulations of dichlorvos against adult H. rubidus and Oesophagostomum spp. in artificially infected growing pigs. Also the effect of the newer V 22 formulation of dichlorvos is compared with that of the original V 3 formulation against naturally acquired "strongyle" infestations in adult pigs.
* Present
address: Medical Research Council, National Institute for Medical Research, Mill Hill, London,
N.W·7·
** Present address:
Department
shire.
:j: Atgard, a Shell trade-mark. V3-an extruded resin pellet formulation intended for application as a feed dressing; V 13-a coated version of the V 3 formulation designed for use in premix feedstuffs; V2 2-similar to V3 but different release rate characteristics allow a lower dose-rate to be effectively employed. PFI18-An experimental formulation for incorporation into pelleted feedstuffs.
xxii
BRITISH VETERINARY JOURNAL,
12 9,
3
MATERIALS AND METHODS
In Experiment I, 25 worm-free castrated Landrace pigs were stratified on the basis of body weight, then allotted at random to five groups of five pigs. Each group was housed separately in a pen with a concrete floor which was cleaned daily. The pigs were fed a balanced diet of pelle ted meal (16 per cent crude protein) once daily to a commercially acceptable feed scale. Animals were between 9-IO weeks of age when infected orally with 6000 Hyostrongylus and 24,000 Oesophagostomum spp. (0. dentatum and O. quadrispinutatum) infective third-stage larvae which had been collected from cultured faeces of experimentally infected pigs. Dichlorvos therapy was effected by mixing the appropriate quantity of the formulated product into the feed of each individual pig forty days after infection, as follows: Group I-VI3, 35 mg/kg; Group 2-PFII8, 35 mg/kg; Group 3-V3, 35 mg/kg; Group 4-V22, 13 mg/kg; Group 5 acted as an infected, untreated control. Faecal egg counts and cultures were carried out on days -8, 0 (the day of infection, 21, 33, 40, 43 and 47. Forty-seven days after infection, i.e. seven days after treatment, the pigs were killed. To aid worm counting, food was withheld for the last 24 hours. The methods of processing of the stomachs and large intestines for worms, which were collected, identified and individually counted, were similar to those described previously (Taffs, 1971). Anthelmintic activity was assessed by noting the effect of the different formulations on faecal egg counts and on cultures, and by comparing the worm burdens of the treated groups with those of the untreated control group (controlled test). In Experiment 2, worm eggs counts and faecal cultures were carried out on faecal samples taken at random from 25 adult pigs in a commercial herd. Twelve sows with the highest egg counts were chosen for the trial. Six sows were dosed with the newer V22 formulation and six others with the original V3 formulation of dichlorvos (see Table II). The anthelmintic was mixed with dry meal and given to pigs individually without water. Individual V22 doses were made up by dividing one sachet holding I 1·2 g total formulation, containing 20 per cent dichlorvos, into four equal portions. Individual V 3 doses consisted of one sachet containing 7·5 g total formulation. Faecal samples were collected on days - 12, 0 and + 7. Anthelmintic activity was assessed by comparing preand post-treatment faecal egg counts and cultures. In both experiments the methods of faecal egg counting (McMaster) and culturing were similar to those previously described (Taffs, 1971). A qualitative and a rough quantitative examination of third-stage larvae recovered from faecal cultures were made. RESULTS AND DISCUSSION
The results are presented in Tables I (Experiment I) and II (Experiment 2). As revealed by an examination of faecal egg counts and cultures, all the experimentally infected pigs except one (Pig NO.9) were shedding Hyostrongylus
TA B LE I
EX PERIM E N T
I. T H E A C TION OF FOUR DIFFE R ENT FOR MULAT I ONS OF D1 C H LO R VOS AG A INST ADULT E X PE RI MENTAL L Y I N F ECTE D P I GS
"Strongyle" faecal egg counts (eggs/g) Dichlorvos Weight at Days after infection f ormulation Group dose Pig treatNo. rate No. meet (kg) - 80 (mg/kg ) 21 40 43 47 33
H . rubidus and Oesophagostomum
SPP. I N
Parasites found post mortem (Day 47 ) Oesophagostomum spp.
Hyostrongylus Individual
Group Total
Average
Percentage efficiency
t>:1
'Tl
Group
Individual T otal
Average
Percentage efficiency
....'Tl 0
>
0
too<:
V I3 35
2
P F I18 35
3
V3 35
I 2 3 4 5
28 51 60 41 32
0 0 0 0 0
0 0 0 0 0
100 100 0 100 200
67 00 3 00 3 00 19 00 200
57 00 4 00 4 000 3 000 39 00
0 0 0 0 0
0 0 0 0 0
3 13 0 2 0 0
6 7 8 9 10
33 46 57 45 36
0 0 0 0 0
0 0 0 0 0
100 0 100 0 0
200 800 100 200 2200
3 00 1700 5 600 3 00 2 100
0 0 0 0 0
100 0 0 0 0
266 0 2 0 0
II
40 59 57 43 43
0 0 0 0 0
0 0 0 0 0
100 100 100 100 100
3900 1000 10 0 2000 3700
6400 6200 200 5 600 4 00
0 0 0 0 0
0 0 0 0 0
25 0
18 19 20
50 45 55 49 41
0 0 0 0 0
0 0 0 0 0
0 100 100 200 100
100 100 5 00 17 00 700
100 3 00 100 200 5900
0 0 0 0 0
0 0 0 0 0
0 0 2 2
21 22 23 24 25
55 50 49 42 40
0 0 0 0 0
0 0 0 0 0
100 100 100 100 100
100 1500 700 5 00 3700
3 00 65 00 200
0 100* 0 100 100
100 3 00 100 700 4 00*
12 13 14 15 16
4
5 Con trol
V22 13
Not t r eated
I7
200
1800
I
3 15
268
28
63
54
6
96 ' 1
9 6 .6
99 .6
2 0
18 93 1534 634 193 2 2 0 79
99 '9
5
80 7 2
161 4
H . Tubidus a nd 24,000 Oesophagostomum spp . larvae on Day o . Treatment was o n Day 40 . ... Oesophagostomum worms observed in faeces o n egg coun ting.
Pigs infec ted wi th 6000
0
0 0 0 0 0
0
0 0 7 0 I
8
0 0 0 0 0 0 0 0 0 0 40 70 4 27 0 0
0
100
'Tl 'Tl
0 C
~ t)
2
9 8 '7
.... 0 ::z:: t'"
0
~
<:
0
0
100
0
r:Jl
'Tl
0
~
0
0
100
s::C
S .... 0
Z
r:Jl
77 1
154
il ~:
TABLE II EXPERIMENT 2. THE EFFECT OF DICHLORVOS FORMULAT ION V22 ON "STRO NGYLE" FAECAL EGG COUNTS (EGGS/G FAECES) AND CULTURES IN ADULT PIGS COMPARED WITH THE ACTION OF THE V3 FORMULATION
II ~.
Day Sow No.
Dichlorvos formulation treatment
o Dosing
- 12
Culture Des.
V22
63 00
+++
76 0
3s00
+ + ++
99
2000
++ +
104
1600
+++
106
2000
+++
119 11 6
V3
Hyo. 800 + (10)
+ (1)
100
+
0
+ (1)
Hyo.
23 00
+++
0
+ (6)
0
+ (1)
+ (2)
600* 1200
++
1700
113
1000
+ +
100
102
70 0
+ (35)
:I:
<: >-l trl ::0 .....
~...::
t.-.
++
C
0
++ + (1)
0
+ + +
0
+++
0
+ (17)
~
>
t' ~
'"
~
<.>::>
1100
+ (50) ++ +
0 0
* Fall in egg count from Day - 12 is probably a reflection of effect of weaning on p eriparturient egg rise since these two pigs weaned their litters between days - 12 and o.
d enotes number of larvae recovered.
~ ..... >-l ..... rFJ
0
ISOO
** With litter . + to + + + +
II
trl
0 + (1)
6S
+ ++
+ (18)
0
1000
+++
0
++++
+++
2200
+ (5)
Des.
4800
3900
112
+++ + (46)
200
++++
Hyo.
100*
++
2300**
Egg count Des.
SOo
122
Culture
Egg count
Egg count
48
+ 7
Culture
EFFICACY OF FOUR DICHLORVOS FORMULATIONS
xxv
eggs in the faeces at least as early as the 2 I st day. All the Oesophagostomum infections except four (Pigs No. I I, 13,23,20) had become patent by that time. By the 33rd day all pigs were shedding both Hyostrongylus and Oesophagostomum eggs in the faeces. The medicated feed was eaten without hesitation. No side-effects were observed. Three and seven days post-treatment, the faecal egg counts of all the treated pigs except one (Pig No.6) were reduced to zero. A fall in egg counts was also noted in two (Pigs No. 22, 25) of the controls and Oesophagostomum worms were observed in the faeces of both animals on the 43rd (Pig No. 22) and 47th (Pig No. 25) days during egg counting. From the recovery of Hyostrongylus worms post mortem the activities of the V 13, PF I 18 and V 22 formulations of dichlorvos compared very favourably (96'1,96.6,99'9 per cent effective) with that of the V 3 formulation (99.6 per cent effective). A similarly high activity (99'4 per cent) of the latter commercial product against adult Hyostrongylus was observed in previous work (Jacobs et al. 1970). Efficacy values of roo, 98'7, 100 and roo per cent were recorded against Oesophagostomum for the VI3, PFII8, V3 and V22 formulations respectively. These results must, however, be interpreted with caution as although only eight worms were recovered from the 15 treated pigs, no worms were found in two of the controls (Pigs No. 24, 25). The egg-count and culture data showed that good "takes" were achieved and that a rapid drop occurred inthe control pigs after the 40th day. Although it is conceivable that these data reflect a natural expulsion of adult worms occurring at that time, the possibility that the control pigs may have ingested faeces containing dichlorvos pellets originating from the treated animals and transmitted via the common clearing passage could not be totally excluded. In Experiment 2, the two formulations of dichlorvos were eaten with the dry meal quite readily and full doses were consumed. Prior to dosing, all the pigs were naturally infected with Oesophagostomum and three (Sows No. 760, 106, 122) were also infected with Hyostrongylus. Seven days after dosing the "strongyle" egg counts were reduced to zero in all 12 pigs. Only one culture (Sow No. 122) was positive in the group treated with the V3 formulation. This indicated that the commercial formulation was almost roo per cent effective against adult Oesophagostomum, and this is in agreement with the results obtained in Experiment I and previously (Jacobs, 1968; Forstner & Matzke, 1969; Taffs, 1969; Jacobs et al., 1971). An examination of faecal cultures from the V22 dosed group seven days after treatment revealed the probably complete clearance of worms from one pig (Sow No. 99). The results of the other five indicated that only a few Oesophagostomum worms remained after dosing. No Hyostrongylus worms were recovered in culture from the three infected pigs after dosing with either formulation. This confirms the high activity shown against Hyostrongylus by both formulations in Experiment I and the V3 formulation in previous work (Forstner & Matzke, 1969; Jacobs et al., 1970). It is unlikely that the fall in egg count was indicative of only a suppression of egg production since actual expulsion of both genera of worms followed treatment in Experiment I.
xxvi
BRITISH VETERINARY JOURNAL, 129,3
This work has shown that the newer VIg, PFII8, and V22 formulations of dichlorvos are as efficient, or very nearly as efficient, as the original V g formulation in expelling adult Hyostronglus from pigs. The results also indicate, although not unequivocally so, since few worms were found in the controls, that the VIg, PFII8 and V22 formulations are as effective, or nearly as effective, as the V g product in removing Oesophagostomum. ACKNOWLEDGEMENTS
The authors thank Dr A. J. Probert for the supply of infective H. rubidus larvae, and Professors J. A. Laing and J. L. Hancock for providing laboratory facilities for one of us (L.F.T.). REFERENCES FORSTNER, M.j. & MATZKE, P. (196g). Dt. tieriirztl. Wschr. 76, 283. JACOBS, D. E. (1968). Vet. Rec. 83, 160. JACOBS, D. E., CURRAN, M. F. & TAFFS, L. F. (1971). Res. vet. Sci. 12, JACOBS, D. E., TAFFS, L. F ., LEAN, I. j. & CURRAN, M . F. (1970). Br. TAFFS, L. F. (1969). Vet. Rec. 85, 166. TAFFS, L. F. (1971). Vet. Rec. 165'
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