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Grootfontein Agric 2017, 17(1), 22-35 Snyman M.A. et al.

22

ARE POUR-ON PESTICIDES STILL EFFECTIVE IN KILLING LICE WHEN

APPLIED AT ALTERNATIVE APPLICATION SITES IN ANGORA GOATS?

M.A. Snyman#, J.N. Snyman & M. van Heerden

Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg (EC), 5900 #Email: [email protected]

INTRODUCTION

South Africa produced 2.4 million kg mohair from 705 000 Angora goats in 2013, which represented

53% of the world’s mohair production (Mohair Review, 2013). South African mohair, or Cape Mohair

as it is known, is renowned for its excellent quality. Lice infestation has a major impact on the

production of mohair in South Africa. Lice irritate the goats’ skin, and this causes them to repeatedly

scratch at the irritations. The continuous scratching causes damage to the mohair fibres, resulting in a

poorer quality.

Brown et al. (2005) did a study to determine the effect of lice infestation on the quantity and quality of

mohair produced by Angora goats. One group of goats was treated with a pesticide and the other group

was not treated. The results showed that the treated group produced significantly more mohair (2.12 kg)

of better quality with less damage to the hair fibres than the untreated goats (1.85 kg). This 25%

difference in mohair production could have a major impact on the income from mohair production if

one takes into account the current average price of R251.49 per kg for mohair (MSA, 2016).

There are two different species of lice that are commonly found on Angora goats (McFarlane, 2016;

Talley, 2016) namely red lice (Bovicola limbata) and blue lice (Linognathus stenopsis). Red lice feed

mainly on the dead flakes of skin and skin secretions, while blue lice attach to the goat while feeding

on blood. The most common practice used by farmers to treat Angora goats for lice infestation is the

application of pesticides. There are three main classes of pesticides, namely organo-phosphates (OP),

synthetic pyrethroids (SP) and insect growth regulators (IGR). The three types of pesticides use

different methods to kill the lice. IGR pesticides work by preventing the young nymphs from moulting

or the eggs from hatching. This kills the lice and prevents further nymphs from hatching. OP and SP

kill the lice directly, though use different ways to accomplish this. Most pesticides do not kill the eggs.

When treating goats with pesticides, another problem arises, namely the pesticide residue that remains

on the hair fibres after the goats have been shorn (Savage, 1998). The residues in the mohair may cause

skin irritation when used in the production of clothing, if the concentration of the residue is too high.

Another source of concern is that when the oils in the mohair, such as lanolin, are extracted for use in


23

other products, some of the pesticide residues are extracted with the oils. These oils are often used in

the production of beauty products, which are usually applied directly onto the skin. The pesticide residue

could cause skin irritation which might lead to more severe skin conditions.

Pesticide residues in mohair also pose an occupational hazard to shearers, farm workers and other

mohair handlers through possible absorption through their skin (Savage, 1998). Another cause for

concern is the fact that the pesticide gets washed out of the hair during processing (Russel, 1994). This

pesticide then forms part of the effluent water that may be pumped back into the environment. This may

contaminate the water table and rivers, as well as cause damage to the local flora and fauna.

Consumer demand for eco-friendly products is rapidly increasing and this has led to stricter

environmental guidelines for effluent disposal from scouring and processing plants. In February 1999,

the European Union (EU) included textile products as part of its ecolabel requirements (Evans, 2007).

The EU Ecolabel for textiles enables consumers to recognise garments that are made from clean, low

pesticide residue fibres. The EU Ecolabel standards stipulate the maximum allowed levels of pesticide

residue for mohair to be 0.5 ppm for SP, 2 ppm for OP and 2 ppm for IGR (EU Ecolabel, 2015).

The OEKO-TEX® Standard 100 is a certification system for all types of textiles (OEKO-TEX, 2016).

For Product class I, which is textile articles for baby clothes and toddlers up to the age of 3 years, the

maximum pesticide limit is 0.5 mg/kg. For the other three classes, including from clothes that will be

worn close to the skin up to curtains and upholstery, the maximum pesticide limit is 1.0 mg/kg. Studies

have shown that concentration of the residue in the mohair remains above the standards three months

after the goats have been dipped. This poses a challenge to the farmers when their goats develop lice

infestations less than three months before the goats are to be shorn.

A possible method of reducing the amount of pesticide residue in the hair might be to only apply a pour-

on pesticide to the head and the base of the tail. The effectiveness in still killing lice of by applying

pesticides to areas alternative than the back line of Angora goats was evaluated in this study.

MATERIALS AND METHODS

The study was conducted under kraal conditions at the Grootfontein Agricultural Development Institute.

Twenty-four 4-year old Angora goats, which had not received any pesticide treatment since September

2015, were used in this study. The goats had all been shorn during December 2015. Twelve of the goats

were shorn during the week of 21 April 2016.


24

Two different types of pesticides were used during the experiment, an insect growth regulator (Pesticide

T) and a synthetic pyrethroid, which is a contact insecticide (Pesticide W). During the week of 25 April

2016, initial lice counts were done on all the goats before the application of the pesticides. The long and

short haired goats were subsequently divided into 4 groups each, as indicated in Table 1, on a stratified

lice count basis.

Table 1. Experimental layout

Pesticide Item Long hair Short hair

Back line Ears / Tail Back line Ears / Tail

Pesticide T

Group name TBL TEL TBS TES

Initial lice count 83.3 81.0 49.7 49.7

Number of goats 3 3 3 3

Pesticide W

Group name WBL WEL WBS WES

Initial lice count 65.3 64.7 39.7 39.3

Number of goats 3 3 3 3

The pesticide treatments were applied at the recommended rate of the respective manufacturers. For

Pesticide T, animals were treated according to their body weight at a dosage rate of 5 ml per 10 kg body

weight. One of the long hair and one of the short hair groups received the treatment as a single strip

down the middle of the back line between the poll and the base of the tail (conventional application

method). For two other groups, the same dose was applied at the base of the tail and at the base of the

ears (alternative application methods). For the pesticide W group, animals were treated according to

their body weight at a dosage rate of 2 ml per 10 kg body weight. The treatment was applied as a single

strip from the poll to the base of the tail, to one of the long hair and one of the short hair groups. For

the remaining two groups, the same dose was applied at the base of the tail and at the base of the ears.

Animals of each group were housed in separate pens in their treatment groups to prevent cross

contamination between treatments. The pens had ample sunshine, as well as protection against rain. The

animals received lucerne hay and fresh, clean water on an ad libitum basis.

The animals were part of the normal animal health program of the Grootfontein Agricultural

Development Institute and received vaccinations according to the program. As the animals were

handled regularly, it was easy to monitor their clinical health. A veterinarian was part of the project

team and was responsible for the monitoring. No artificial lice infestation was done. The experiment

was carried out using the natural lice infestation present on the goats at the start of the experiment.

During the experiment, if a goat had more than a total body count of 200 lice, it would have been


25

removed from the experiment and treated for the infestation. The project protocol was approved by the

Ethical Committee of the Grootfontein Agricultural Development Institute (Approval Number:

GVE/AP5/30/3).

Lice counts were done on all animals in each treatment group over an 11-week period. The live lice

were counted macroscopically at ten predetermined sites (five on either side of the body; Figure 1). At

Site 1, all live lice in a 3 cm radius around the ear and around the eye were counted. At the other sites,

all live lice in a 10 cm x 10 cm area of the fleece were counted. In the long haired animals, the fleece

was opened all over these 10 cm x 10 cm areas to inspect the skin area for live lice. The counting sites

at the right hand side of the animals were always counted first and these were denoted as R1 to R5.

Those on the left hand side were noted as L1 to L5.

Figure 1. Sites at which live lice were counted

The effect of application site on effectiveness in killing lice was determined by employing a general

linear model, including pesticide, application site, length of hair, counting site and date as treatment

effects. For analyses involving the effect of hair length, Day 0 lice counts for the respective groups were

included as a covariate to account for any initial differences in lice count between short and long hair

groups. The SAS statistical package (SAS, 2009) was used for the analysis.


26

The following was calculated from the recorded data:

The effect of application site on effectiveness in killing lice of each pesticide

The effect of hair length on effectiveness in killing lice of each pesticide

Trends in lice counts for each group and each counting site.

RESULTS

Total lice counts over the experimental period are summarised in Table 2. From Table 2 it can be seen

that the lice counts of the long hair animals were higher at the start of the experiment than those of the

shorter hair animals. The animals were, however, divided into the groups in such a way that the start

lice count did not differ between the application sites within hair lengths and pesticides. That means

TES (pesticide T, ears/tail application, short hair) and TBS (pesticide T, backline application, short hair)

had the same start lice count. The same applied for the other groups (See Table 2, Day 0 lice counts).

At Day 7, there were significant differences among the Pesticide T groups. TEL animals had more lice

than animals in groups TES and TBS. TBL animals also had significantly more lice than TES and TBS

animals. At Day 14, the TES animals had fewer lice than the TEL and TBL animals, while the TBS

animals also had fewer lice than the TBL animals. The only significant differences among the Pesticide

T groups at Day 21 were where the TEL and TBL animals had more lice than the TBS animals. The

TEL animals also had more lice than the TBS animals on Day 28 and Day 42. At Day 42, the TEL

animals also had more lice than the TES animals. From Day 56 onwards, there were no further

significant differences among the Pesticide T groups.

There were no significant differences among the Pesticide W groups at Day 7 and 14. At Day 21 the

WBL animals had significantly more lice than the WEL animals. From Day 28 onwards, there were no

further significant differences among the Pesticide W groups.


27

Tab

le 2

. Tot

al li

ce c

ount

s (±

s.e

.) o

f th

e di

ffer

ent g

roup

s ov

er th

e ex

peri

men

tal p

erio

d

Gro

up

D

ay 0

D

ay 7

D

ay 1

4 D

ay 2

1 D

ay 2

8 D

ay 4

2 D

ay 5

6 D

ay 6

3 D

ay 7

7

Pes

tici

de

T g

rou

ps

TE

S

49.7

± 2

3.3

15.7

b ± 1

9.4

7.7a ±

17.

9 16

.0 ±

14.

8 16

.7 ±

21.

0 8.

7a ± 2

6.3

17.0

± 1

3.4

17.7

± 1

7.2

12.7

± 1

5.9

TB

S

49.7

± 2

3.3

18.0

b ± 1

9.4

18.7

a ± 1

7.9

2.3a ±

14.

8 11

.3a ±

21.

0 8.

7a ± 2

6.3

10.3

± 1

3.4

14.7

± 1

7.2

18.3

± 1

5.9

TE

L

81.0

± 2

3.3

72.7

a ± 1

9.4

52.0

b ± 1

7.9

40.0

b ± 1

4.8

66.7

b ± 2

1.0

74.0

b ± 2

6.3

23.3

± 1

3.4

31.7

± 1

7.2

42.3

± 1

5.9

TB

L

83.3

± 2

3.3

66.0

a ± 1

9.4

73.3

b ± 1

7.9

47.7

b ± 1

4.8

47.0

± 2

1.0

61.0

± 2

6.3

38.0

± 1

3.4

51.0

± 1

7.2

41.3

± 1

5.9

Pes

tici

de

W g

rou

ps

WE

S

39.3

± 2

3.3

5.7

± 19

.4

24.7

± 1

7.9

11.0

± 1

4.8

10.0

± 2

1.0

9.7

± 26

.3

12.0

± 1

3.4

26.7

± 1

7.2

26.0

± 1

5.9

WB

S

39.7

± 2

3.3

24.3

± 1

9.4

6.3

± 17

.9

11.0

± 1

4.8

15.0

± 2

1.0

21.7

± 2

6.3

9.3

± 13

.4

17.3

± 1

7.2

27.3

± 1

5.9

WE

L

64.7

± 2

3.3

27.7

± 1

9.4

22.3

± 1

7.9

7.0a ±

14.

8 7.

0 ±

21.0

12

.0 ±

26.

3 13

.3 ±

13.

4 19

.3 ±

17.

2 27

.3 ±

15.

9

WB

L

65.3

± 2

3.3

16.0

± 1

9.4

41.3

± 1

7.9

45.3

b ± 1

4.8

5.7

± 21

.0

17.7

± 2

6.3

10.7

± 1

3.4

26.0

± 1

7.2

26.3

± 1

5.9

a, b V

alue

s w

ith

diff

eren

t sup

ersc

ript

s di

ffer

sig

nifi

cant

ly (

P <

0.05

) w

ithi

n pe

stic

ides

TE

S =

Pes

tici

de T

, Ear

s/ta

il ap

plic

atio

n, S

hort

hai

r

TB

S =

Pes

tici

de T

, Bac

klin

e ap

plic

atio

n, S

hort

hai

r

TE

L =

Pes

tici

de T

, Ear

s/ta

il a

ppli

cati

on, L

ong

hair

TB

L =

Pes

tici

de T

, Bac

klin

e ap

plic

atio

n, L

ong

hair

WE

S =

Pes

tici

de W

, Ear

s/ta

il a

ppli

cati

on, S

hort

hai

r

WB

S =

Pes

tici

de W

, Bac

klin

e ap

plic

atio

n, S

hort

hai

r

WE

L =

Pes

tici

de W

, Ear

s/ta

il a

ppli

cati

on, L

ong

hair

WB

L =

Pes

tici

de W

, Bac

klin

e ap

plic

atio

n, L

ong

hair


28

Total lice counts over the experimental period of the Pesticide T and Pesticide W groups are shown in

Figures 2 and 3 respectively.

Figure 2. Total lice counts over the experimental period of the Pesticide T groups

(TES = Pesticide T, Ears/tail application, Short hair; TBS = Pesticide T, Backline application, Short hair; TEL = Pesticide T, Ears/tail application, Long hair; TBL = Pesticide T, Backline application,

Long hair)

From Figure 2 it can be seen that lice counts of all groups decreased from Day 0 until Day 21 for the

Pesticide T groups. From then onwards for the rest of the trial the lice numbers remained about constant

for the short hair groups (TES and TBS). In the long hair groups (TEL and TBL), there was an increase

in lice numbers after Day 21 up until Day 42. Thereafter the lice numbers again decreased until Day 56,

after which it increased again until Day 77. For most of the groups the lowest lice counts were reached

on Day 56.

From Figure 3 it can be seen that lice numbers of all the Pesticide W groups decreased from Day 0 until

Day 7. From Day 7 until Day 28 there was no obvious trend that could be observed among the different

groups. WBS and WEL continue to decrease during this period, while WES and WBL first increased

and then decreased during this three week period. After Day 28, however, there was not much change

in lice numbers until Day 56. After Day 56 there was a slight increase in lice numbers until the end of

the experiment.

0

10

20

30

40

50

60

70

80

90

0 7 14 21 28 42 56 63 77

Nu

mb

er o

f li

ce

Days after treatment

TES TBS TEL TBL


29

Figure 3. Total lice counts over the experimental period of the Pesticide W groups

(WES = Pesticide W, Ears/tail application, Short hair; WBS = Pesticide W, Backline application, Short hair; WEL = Pesticide W, Ears/tail application, Long hair; WBL = Pesticide W, Backline

application, Long hair)

The effect of application site and length of hair on average lice numbers over the experimental period

are given in Table 3 for the pooled data, as well as for Pesticide T and Pesticide W.

Table 3. Effect of application site and length of hair on average lice numbers (± s.e.) over the

experimental period

Effect Lice count P value

Pooled data

Ears/Tail 28.1 ± 3.1 0.8011

Backline 29.2 ± 3.1

Short hair 18.7 ± 3.1 0.0044

Long hair 31.4 ± 3.1

Pesticide T

Ears/Tail 35.9 ± 5.5 0.8948


Short hair 20.9 ± 5.5 0.0022


Pesticide W

Ears/Tail 20.3 ± 2.5 0.3674


Short hair 16.4 ± 2.5 0.4251


0

10

20

30

40

50

60

70

0 7 14 21 28 42 56 63 77

Nu

mb

er o

f li

ce

Days after treatment

WES WBS WEL WBL


30

From Table 3 it can be seen that there was no difference in lice count between application sites for the

pooled data, while the long hair animals had higher lice counts than the short hair animals. There was

also no difference in lice counts between application sites for either pesticides. For Pesticide T, the long

hair animals had significantly more lice than the shorter hair animals, while there was no difference in

lice counts between long and short hair animals in the Pesticide W groups.

Red lice at site R1 – around the ear

Red lice at site R2 – neck area


31

The effect of application site on average lice numbers over the experimental period for Pesticide T for

the different sites on the body where lice were counted are summarised in Figure 4. The same data for

Pesticide W are given in Figure 5. There were no differences in lice counts at the different counting

sites between the ears/tail and the backline application sites of the Pesticide T groups (Figure 4), with

the exception of R2. At R2, which is the right hand neck area, there were more lice with the ears/tail

method than with the backline method. There were no differences in lice counts at the different counting

sites between the ears/tail and the backline application sites of the Pesticide W groups (Figure 5).

Figure 4. The effect of application site on lice numbers at the different counting sites for Pesticide T

(P <0.05 at R2)

Figure 5. The effect of application site on lice numbers at the different counting sites for Pesticide W

(P >0.05 all sites)

0

1

2

3

4

5

6

7

8

9

R 1 R 2 R 3 R 4 R 5 L1 L2 L3 L4 L5

Nu

mbe

r of

lice

Counting site

Pesticide T

Ears/Tail Backline

0

1

2

3

4

5

6

7

8

9

R 1 R 2 R 3 R 4 R 5 L1 L2 L3 L4 L5

Nu

mb

er o

f lic

e

Counting site

Pesticide W

Ears/Tail Backline


32

The effect of length of hair on average lice numbers over the experimental period for the different sites

on the body where lice were counted are summarised in Figures 6 and 7 for Pesticide T and Pesticide

W respectively. There were significantly more lice at all counting sites in the long hair animals than in

the shorter hair animals with Pesticide T (Figure 6). As the long hair animals had significantly more

lice than the short hair animals, this could be expected. These results, however, showed that the higher

infestations were spread all over the body and not only located at some of the counting sites. In the

Pesticide W groups (Figure 7) there were also significantly more lice at the R1, R2, R5, L2 and L5

counting sites in the long hair animals than in the shorter hair animals.

Figure 6. The effect of length of hair on lice numbers at the different counting sites for Pesticide T

(P <0.05 all sites)

Figure 7. The effect of length of hair on lice numbers at the different counting sites for Pesticide W

(P <0.05 at R1, R2, R5, L2 and L5)

0

1

2

3

4

5

6

7

8

9

R 1 R 2 R 3 R 4 R 5 L1 L2 L3 L4 L5

Nu

mbe

r of

lice

Counting site

Pesticide T

Short hair Long hair

0

1

2

3

4

5

6

7

8

9

R 1 R 2 R 3 R 4 R 5 L1 L2 L3 L4 L5

Nu

mbe

r of

lice

Counting site

Pesticide W

Short hair Long hair


33

DISCUSSION

With Pesticide T, which is an insect growth regulator, lice counts in all groups were reduced within the

first seven days. In the shorter hair animals, this initial decrease was more than in the long hair animals.

In both the long and short hair animals the lice counts decreased until Day 21. It then remained at a low

level in the short hair animals, but increased in the longer hair animals. This pesticide is supposed to

prevent the development of immature lice present in the fleece at application and those that hatch from

eggs in the following 20 weeks. It is also supposed to produce a rapid decline in lice numbers with all

adult lice dying by 14 weeks. It is obvious that these claims did not realise in the current experiment.

Adult lice live for about 50 to 60 days. As this pesticide does not directly kill the lice, the adult lice

continue laying eggs. The eggs are attached to the hair. If an egg is attached higher up the hair fibre, the

longer hair might influence the effectiveness of the pesticide by preventing the egg from coming in

contact with the active ingredient. After Day 56, lice counts in the long hair groups further increased.

Even though the long hair animals had a higher initial lice count, it would seem that the insect growth

regulator pesticide was not as effective in the longer hair animals. The reason for this is that the initial

lice count was corrected for in the analysis for the effect of hair length.

In the Pesticide W groups, which is a contact insecticide, lice counts dropped within seven days.

Thereafter no specific trend was observed until Day 28. As with the long hair groups of Pesticide T,

lice counts in both short and long hair groups increased after Day 56. There was no difference in lice

counts between long and short hair animals in the Pesticide W groups. The contact pesticide therefore

was equally effective in long and short hair animals. The manufacturer’s claim of 13 weeks’ protection

against reinfestation was obviously also not realised in this experiment.

The results of this study indicated that there was no difference in effectiveness of either pesticide

whether it was applied in the conventional manner along the backline, or only at the ears and tail.

Furthermore, although the pesticide was only applied at the ears and tail in some groups, lice counts at

all the counting sites over the body decreased over the experimental period. This implies that the active

ingredients must have moved from the application site over the body, or was carried across the body by

lice moving across the body and coming into contact with other lice, especially in order to kill red lice,

which do not suck blood. The red lice would only have been killed if they got into direct contact with

the pesticide.

CONCLUSIONS

From the results of this experiment it is evident that the effectiveness of the two pour-on pesticides used

in this study in killing lice was not affected when the pesticide was applied at an alternative site on the

body. The contact pesticide was equally effective in long and short hair animals, while it seems that the


34

insect growth regulator was more effective when applied to short hair animals, although lice counts in

the long hair animals were also reduced.

Further investigations could probably be done on a larger scale and including more contact pesticide

products in co-operation with the mohair industry. Determination of the pesticide residues could then

also be done. Taking into account a possible loss of 25% in mohair production, combined with a

decrease in quality, farmers cannot afford to leave lice infestations untreated.

ACKNOWLEGDEMENTS

Mohair South Africa is acknowledged for permission to use their Angora goats for the project.

This project was presented at the Eskom Expo for Young Scientists International Science Fair during

October 2016.

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Russel, I., 1994. Pesticides in wool: downstream consequences. Wool Tech. Sheep Breed. 42(4), 344-

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SAS, 2009. SAS Procedures Guide, Version 9.1.3. Cary, NC, SAS Institute Inc.

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web.pdf Date accessed: 18/06/2016.

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