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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: Gretha Snyman

 

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 may cause 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 the red lice (Bovicola limbata) and the 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 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 of 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.

 

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 200 lice, it would have been 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.

 

The following was calculated from the recorded data:

 

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).

 

As the number of lice differed on Day 0 between Pesticide T and Pesticide W, although not significantly, it was decided to present the results separately for each pesticide to prevent any possible bias due to this initial difference.

 

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.

 

Table 2. Total lice counts (± s.e.) of the different groups over the experimental period

 Group

Day 0

Day 7

Day 14

Day 21

Day 28

Day 42

Day 56

Day 63

Day 77

Pesticide T groups

 TES

49.7 ± 23.3

15.7b ± 19.4

7.7a ± 17.9

16.0 ± 14.8

16.7 ± 21.0

8.7a ± 26.3

17.0 ± 13.4

17.7 ± 17.2

12.7 ± 15.9

 TBS

49.7 ± 23.3

18.0b ± 19.4

18.7a ± 17.9

2.3a ± 14.8

11.3a ± 21.0

8.7a ± 26.3

10.3 ± 13.4

14.7 ± 17.2

18.3 ± 15.9

 TEL

81.0 ± 23.3

72.7a ± 19.4

52.0b ± 17.9

40.0b ± 14.8

66.7b ± 21.0

74.0b ± 26.3

23.3 ± 13.4

31.7 ± 17.2

42.3 ± 15.9

 TBL

83.3 ± 23.3

66.0a ± 19.4

73.3b ± 17.9

47.7b ± 14.8

47.0 ± 21.0

61.0 ± 26.3

38.0 ± 13.4

51.0 ± 17.2

41.3 ± 15.9

Pesticide W groups

 WES

39.3 ± 23.3

5.7 ± 19.4

24.7 ± 17.9

11.0 ± 14.8

10.0 ± 21.0

9.7 ± 26.3

12.0 ± 13.4

26.7 ± 17.2

26.0 ± 15.9

 WBS

39.7 ± 23.3

24.3 ± 19.4

6.3 ± 17.9

11.0 ± 14.8

15.0 ± 21.0

21.7 ± 26.3

9.3 ± 13.4

17.3 ± 17.2

27.3 ± 15.9

 WEL

64.7 ± 23.3

27.7 ± 19.4

22.3 ± 17.9

7.0a ± 14.8

7.0 ± 21.0

12.0 ± 26.3

13.3 ± 13.4

19.3 ± 17.2

27.3 ± 15.9

 WBL

65.3 ± 23.3

16.0 ± 19.4

41.3 ± 17.9

45.3b ± 14.8

5.7 ± 21.0

17.7 ± 26.3

10.7 ± 13.4

26.0 ± 17.2

26.3 ± 15.9

a, b Values with different superscripts differ significantly (P <0.05) within pesticides

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

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

 

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.

 

 

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

 Backline

34.8 ± 5.5

 Short hair

20.9 ± 5.5

0.0022

 Long hair

44.3 ± 5.5

Pesticide W

 Ears/Tail

20.3 ± 2.5

0.3674

 Backline

23.6 ± 2.5

 Short hair

16.4 ± 2.5

0.4251

 Long hair

18.6 ± 2.5

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

 

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)

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 are spread all over the body and are 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)

 

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 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 decreased 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.

 

REFERENCES

Brown, L., Van der Linde, T.C. de K., Fourie, L.J, & Horak, I.G., 2005. Seasonal occurrence and production effects of the biting louse Damalinia limbata on Angora goats and 2 treatment options. J. S. Afr. Vet. Ass. 76(2), 74-78.

Evans, D., 2007. Guidelines for producing European eco-label, low or nil residue wool. Farmnote, Note: 265 November 2007 (Replaces Factsheet 131), Department of Agriculture and Food, Western Australia.

EU Ecolabel, 2015. EU Ecolabel Textile Products User Manual. Commission Decision for the award of the EU Ecolabel for textile products (2014/350/EU). Version 1.0 March 2015. User Manual (online). Available: http://ec.europa.eu/environment/ecolabel/documents/User_manual_textile.pdf  Date accessed: 18/06/2016.

McFarlane, 2016. Rooiluise By Angorabokke (online). Available: http://www.angoras.co.za /page/rooiluise. Date accessed: 20/06/2016.

Mohair Review, 2013. (online) Available:  http://www.mohair.co.za/page/industry_review. Date accessed: 09/07/2016.

MSA, 2016. Market Report Catalogue: 201606 (online). Available: http://www.mohair.co.za/uploads/auction/results/201606MarketReport.pdf.  Date accessed: 09/07/2016.

OEKO-TEX, 2016. OEKO-TEX® Standard 100 (online). Available: https://www.oeko-tex.com/media/downloads/Factsheet_OETS_100_EN.pdf Date accessed: 20/06/2016.

Russel, I., 1994. Pesticides in wool: downstream consequences. Wool Tech. Sheep Breed. 42(4), 344-349.

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

Savage, G., 1998. The residue implications of sheep ectoparasiticides. A Report for The Woolmark Company, Canberra, Australia.

Talley, J., 2016. External Parasites of Goats. Oklahoma Cooperative Extension Fact Sheets (online). Available: http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-5175/EPP-7019 web.pdf  Date accessed: 18/06/2016.

 

Published

Grootfontein Agric 16 (1) (22)