- Protocol for selection for resistance / resilience to Haemonchus contortus under South African conditions
PROTOCOL FOR SELECTION FOR RESISTANCE / RESILIENCE TO HAEMONCHUS CONTORTUS UNDER SOUTH AFRICAN CONDITIONS
M.A. Snyman1# & A. Fisher2
1 Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg (EC), 5900, South Africa
2 Queenstown Provincial Veterinary Laboratory, Private Bag X7093, Queenstown, 5320, South Africa
#Corresponding author: Gretha Snyman
Background: The issue of resistance of internal parasite species to worm remedies is widespread throughout South Africa and affects all small stock farmers. Haemonchus contortus is the most important parasite and causes the most losses among sheep in the summer rainfall regions in South Africa. The farm Wauldby, in the Stutterheim district, has a well-documented history of heavy Haemonchus contortus challenge and of Haemonchus resistance to all five major anthelmintic groups on the market prior to 2011. Several anthelmintic resistance trials have been done at Wauldby over the years. The severe anthelmintic resistance problem on the farm has inadvertently resulted in selection of sheep over many years with a high degree of resistance / resilience to internal parasites as drenching with anthelmintics has been largely ineffective. At the end of 2011, a project aimed at selection for resistance to Haemonchus was implemented at this farm.
Aim: The aim of this study was to develop protocols for selection for resistance / resilience to Haemonchus contortus under South African conditions.
Methodologies: Data on faecal egg counts (FEC), Famacha© score (FAM) and body condition score (BCS) recorded from 2011 to 2015 during the parasite resistance trial done on the Wauldby Dohne Merino stud were analysed with various univariate, multivariate and repeatability animal models using the AsReml programme. The results were used to assist in the development of protocols for selection for resistance / resilience to Haemonchus contortus under South African conditions.
Results and Discussion: Two protocols were developed; one for stud breeders and one for commercial producers. In the case of stud animals, recording of individual animals should take place. FEC, FAM and BCS of all lambs could be recorded once before weaning, depending on the rainfall and climatic conditions. All lambs could be drenched after data collection. After weaning, FAM and BCS should be recorded every 14 days until the first week of July when Haemonchus challenge has decreased. FEC should be recorded at the beginning (January) and twice during the peak Haemonchus season (March and May). Lambs should only be drenched when they have a FAM of 2.5 or more. Any lamb that was drenched should be noted and culled. Replacement rams and ewes should be selected from the animals that did not need dosing on the basis of a selection index incorporating FEC, FAM and BCS and breeding values for FEC. In the case of commercial animals, pooled FEC could be taken before weaning. After weaning only ewe lambs should be recorded. FAM and BCS should be recorded every 14 days until the Haemonchus challenge has decreased. FEC should be monitored through monthly pooled FEC samples. Lambs should only be drenched when they have a FAM of 2.5 or more. Any ewe lamb that was drenched should be noted and lambs that needed 2 or more drenchings should be culled.
Conclusions: A protocol for selection for resistance / resilience to Haemonchus contortus under South African conditions has been developed and needs to be validated on various farms before implementation on a wider scale.
Proc. 50th Congr. S. Afr. Soc. Anim. Sci. Port Elizabeth, September 2017