Guidelines for ovine miticides efficacy submissions
Guideline 22
Contents:
1. Introduction
These guidelines apply to acaricidal substances to be submitted to the National Registration Authority (NRA) for clearance where claims are made for the control of itch mite (Psorergates ovis) infestation of sheep. If claims are to be made for other species of mites, comparable data should be presented.
The applicant must show that, using the examination methods and intervals described herein, the product is capable of controlling infestations of mites on all sheep in a treated mob.
No part of these guidelines should be taken to be an alternative to recognised statistical design and analytical methods, but should be used as a basis for the design of trials.
It is the responsibility of the applicant to devise the appropriate experimental procedures which will yield significant, repeatable results. Any departures from the guidelines should be discussed well in advance with the NRA secretariat.
If a claim is made for control of fleece derangement, unequivocal evidence must be presented in the submission that fleece damage caused by infestations of itch mites was significantly reduced over a specified time period in treated sheep compared with untreated controls.
2. Trials
For each new product at least four pen trials are required, two in late winter - spring and two in late summer - autumn.
The following information should be detailed for each trial:
- location;
- date;
- officer-in-charge and other staff or co-operators involved;
- product identity;
- formulation and batch number;
- breed of sheep used;
- season of the year;
- nutritional status of the sheep;
- time since last shearing and length of wool;
- the method of application (dipping, jetting, backline or others) and any departures from label recommendations proposed for the product;
- where artificial rainfall is used to test the efficacy of the product after heavy rain, the method of wetting used and the equivalent in terms of natural rainfall should be stated (eg artificial rain applied via inverted sprinklers, equivalent to a rainfall of 20mm in a storm lasting 30 minutes);
- any other chemical treatment or medication of the treated sheep during the course of the trial;
- use of animals in trials must be in accordance with the principles set down in the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes (1990) and the requirements of any State or Territory legislation controlling the use of animals in research.
2.1 Purpose of the trials
- to demonstrate that the minimum dose rate or concentration of the product that is recommended for commercial use, is capable of reliably controlling itch mites on all sheep that are treated under the proposed conditions for use. Control means reduction of the mite population to non-detectable levels at all post-treatment examinations of treated sheep, in the presence of normal seasonal fluctuations in the population on untreated sheep kept under the same conditions. This could involve trials to show product efficacy under a variety of conditions of use (breed, length of wool, type of equipment, quality of water used as diluent etc);
- to identify peculiarities, contraindications, side effects etc when the commercial formulation of the product is used on sheep;
- to demonstrate that heavy rainfall immediately before or after treatment does not effect the efficacy of the product.
2.2 Establishment of trials
- presence of fleece derangement is not always a good indicator of sheep with detectable infestations of mites. Presence of skin scurf is a fair indicator of infestation and sheep to be examined for suitability in trials should be selected in the first instance on the basis of moderate to heavy deposits of scurf on the skin;
- each trial should consist of an untreated control group and treated groups including at least one treated at the recommended rate with the proposed commercial formulation;
- each group should contain at least 5 sheep with a naturally acquired or stable, artificially induced infestation of itch mites. Sheep included in these groups should be acclimatised to their environment for at least 14 days before the trials begin and, when subjected to skin scraping, should have a mite infestation of ³ 10 mites/200 cm-2 of skin examined.
- the groups of sheep should be kept in pens which allow them normal exposure to prevailing weather;
- all groups in each trial should be fed a standard maintenance ration which will preserve, but not increase, body condition;
- the treated and control groups should be kept under the same conditions, but isolated from direct contact with each other for the duration of each trial.
2.3 Overseas trials
While results of pen trials conducted outside Australia may be submitted and can be used in support of the submission, they will not be considered as alternatives to the Australian trials. Sufficient Australian trials which demonstrate efficacy are necessary.
3. Techniques
3.1 Detection of mites
In all trials, to determine the level of infestation, at least 2 sites on the body should be examined by removing the fleece to skin level from an area measuring about 10cm x 10cm. The sites selected should be on the side of the sheep between a line joining the top of the shoulder and point of the hip and a line joining the bare areas of skin inside the forelimb and hindlimb.
An electric small animal clipper, fitted with a size 40 number 80 blade removes the wool efficiently close to the skin and facilitates scraping. Clippers should be cleaned between sheep by brushing out the comb and cutter and rinsing off accumulated wax with a small quantity of acetone or absolute alcohol. Approximately 2 to 5ml of light medicinal oil or paraffin oil is spread over the skin and the area is scraped using a fixed, blunt blade until an erythematous reaction develops, but no capillary bleeding occurs. The oil and debris from each site is placed onto microscope slides for immediate examination or into a 5ml plastic vial for examination later. If the examination cannot be done within 4 hours the material may be deep frozen. The disadvantage of this is that any mites present will be killed and there will be no movement to assist examination. Adult and immature mites with visible internal detail should be counted and the numbers recorded for each site. Shells and bodies of mites lacking internal detail can be counted separately. Counting can be done with the aid of a stereo or compound microscope.
Mites should be counted as late as possible before treatment. If the period between examination and treatment is more than 24 hours then the interval should be stated.
These techniques may be varied by the applicant. In all cases the methods used should be fully described and the reliability demonstrated in the submission.
3.2 Detection and scoring of skin scurf
Presence of scurf on the skin is a useful indicator of changes in mite infestation after treatment. Scurf can be readily seen when the fleece is parted and is clearly revealed when the wool is removed prior to skin scraping. Presence of scurf should be scored on the basis of 0 - no visible deposit on the skin, 1 - sparse scattered deposit, 2 - a uniformly spread powdery deposit, 3 - a thick deposit with obvious flakes.
3.3 Treatment of sheep
(a) Plunge or shower dips
Sheep should be treated in the manner recommended on the draft label. After charging the dip at the recommended rate the concentration of active ingredient in the dip fluid should be measured by appropriate analytical techniques before, during and at the end of dipping.
The method of application should be clearly detailed:
For plunge dips: the length, depth, number of times sheep are dunked after entering the dip, range of times in the dip and average time in the dip should be recorded. Sheep should be dunked at least twice.
For shower dips: the brand and model of dip used should be stated together with the operating pressure and output of the pump. The length of time that sheep are showered and the combination of upper and lower nozzles used should be stated.
For plunge and shower dips: the method of mixing the chemical in the sump, the method of addition of fresh chemical and amounts added should be recorded.
(b) Backlines
The MLD 100 should form the basis of the proposed treatment regime, taking into consideration the disposition of the chemical as a consequence of the delivery system (solvent and hardware). Claims made in respect of this point should be supported by appropriate data.
(c) Insect growth regulators (IGRs)
Applicants wishing to register IGR based products or any product based on compounds that work over a protracted period must nominate the period of time required to control mites on treated sheep. The time nominated must be based on valid scientific data.
(d) Other systems
Submissions for the registration of other classes of pesticides applied in other ways will be based on these guidelines except where the applicant is of the opinion that the new chemical or treatment method cannot be properly assessed in this way. In such cases discussions should be held with the NRA before the application for registration is completed.
3.3 Inspection of sheep
Skin scrapings from treated and control sheep should be examined and skin scurf scores should be recorded within 24 hours before treatment and at 1, 3, 6, 9 and 12 months after treatment.
4. Formulation changes
All formulation changes require NRA clearance. All such submissions require stability data.
4.1 Minor formulation changes
For example changes in inert ingredients (apart from any that control the disposition of the active) or changes in the concentration of active ingredients require:
- Stability data; and
- Pen trials.
4.2 Major formulation changes
For example, changes to a solvent system controlling the disposition of the active ingredient require:
- Stability data;
- Pen trials;
- Residue data to demonstrate compliance with existing MRLs.
Please Note: Any change of isomers of active ingredients or changes of active ingredients, constitutes a new product and requires a complete submission for registration of a new end use product. This would incorporate data covering all sections of these guidelines.
4.3 Dye changes
Require:
- Stability data;
- Scourability data based on fleeces from at least 5 sheep.
5. Adverse Reactions
In addition to the class of adverse reactions related to the user or the animal treated (data required for all products), the following should also be examined for all products:
(a) Wool staining or damage
The scourability using normal commercial processing for any stains and the extent of any wool damage affecting woolen or worsted processing.
(b) Hide/skin damage
Examination of sheep in pen and field trials should include thorough inspection of the wool and skin for any apparent reaction to the product. If any reaction is seen, the effect of factors such as breed, age, climate, geography and repeated treatment should be investigated and histopathological examinations of affected skin should be made (Britt et al, 1984).
Sheep with visible or palpable reactions should be slaughtered and the affected skins tanned and processed. The effects of treatment should be assessed following scouring, woolskin tanning and processing and fellmongering. This assessment should reflect the variety of processes used commercially. At least 30 tanned and processed woolskins from at least 4 different farms should be examined. The applicant should seek to define the aetiology and pathogenesis of any adverse effects of the product and the duration of damage (eg time for skin to return to normal).
6. References
Australian Code of Practice for the Care and Use of Animals for Scientific Purposes (1990)
Australian Government Publishing Service, Canberra
Britt A G, Cotton C L, Trask J A and Pitman I H (1984)
Effects of a pour-on insecticidal formulation on sheep skin.
Australian Veterinary Journal 61: 329-330
7. Terminology
As in Appendix V Labeling Requirements of Ectoparasiticides for Sheep and Goats
Control
Reduction
of the mite population to non-detectable levels at all post-treatment
examinations of treated sheep, in the presence of normal seasonal fluctuations
in the population on untreated sheep kept under the same conditions.