I am interested in the experience and approach by others when selecting for low WEC and the correlated response in 'hyper sensitivity scouring' in sheep in a winter rainfall environment.
This relationship has been debated for many years. A statement often made has been animals with genetically lower WEC scour more when challenged with nematode larvae. Although some would say a flock of more resistant animals also lower the larval challenge on pasture and the nett result is little different or even better at a mob level.
To my knowledge the accuracy of many of the experiments conducted have suffered from two issues: a) large standard errors of the estimated genetic correlations or b) in WEC selection line studies the error term of the between line comparisons have not included founder effects and genetic drift.
We suspected the early reports suffered from some form of hidden bias as larger studies on broader populations generally had much lower estimates.
This observation led us to do a comprehensive study: the largest to our knowledge ever done to date and used New Zealand dual purpose sheep in an environment where nematode larvae are typically present on pasture year round with a peak in late autumn Pickering et al 2011 http://www.ncbi.nlm.nih.gov/pubmed/22100586
There were ~130,000 records of what Australians call WEC in summer and autumn as lambs and 45,000 records of dag score using animals born over a 20 year period. Dag score is essentially a cumulative trait of scouring and is highly correlated.
The results? Well all parasite egg and dag traits were heritable. For the strongyle egg traits (summer and autumn) and lamb dags at ~the same times the genetic correlations between the WEC and dag ranged from -0.04±0.05 to 0.10±0.06. Pretty clear evidence of very low or zero genetic correlation between the two traits. For Nematodirus eggs they ranged from -0.17±0.06 to 0.01±0.05 which provides a little support for on investigation for less dags at younger ages for this infection but the relationships are very low and its at weaning not autumn!
My summary is that a large amount of scientific literature has been written about the negative genetic relationship between scouring and WEC but the largest study done to date with the lowest standard errors provides little or no evidence to support this relationship. However, that said including both traits in a selection index is a sensible option.
http://www.journalofanimalscience.org/content/90/5/1411.long
Can yo please read the article on 'The use of sheep breeds resistant to internal parasites' at www.aces.edu. It may assist you on the protocol. Good day
Kindly see the following RG links and PDF attachment.
Article Breeding for worm resistance - Whole farm benefits
Article Breeding Sheep in New Zealand for Resistance or Resilience t...
Article Merino ewes bred for parasite resistance reduce larval conta...
https://www.google.com/url?sa=t&source=web&rct=j&url=https://pubmed.ncbi.nlm.nih.gov/15484935/&ved=2ahUKEwjT_uC4kL7wAhUs4zgGHaQUAiIQFjABegQICBAC&usg=AOvVaw0x8BMW1De4SoHdHBkgxn01
https://www.google.com/url?sa=t&source=web&rct=j&url=https://pubmed.ncbi.nlm.nih.gov/29635633/&ved=2ahUKEwjT_uC4kL7wAhUs4zgGHaQUAiIQFjACegQIDhAC&usg=AOvVaw3SZDyfKCV5P4jMMULn7PcJ&cshid=1620615902154
https://www.google.com/url?sa=t&source=web&rct=j&url=https://pubmed.ncbi.nlm.nih.gov/29635633/&ved=2ahUKEwjT_uC4kL7wAhUs4zgGHaQUAiIQFjACegQIDhAC&usg=AOvVaw3SZDyfKCV5P4jMMULn7PcJ&cshid=1620615902154
Hi Dear John Leif Jan-Erik Karlsson
You can read this paper:
Article Signatures of selection in sheep bred for resistance or susc...
You can read this paper:
https://gsejournal.biomedcentral.com/articles/10.1186/1297-9686-22-2-205
Dear John Leif Jan-Erik Karlsson
Article Quantitative trait loci for internal nematode resistance in ...
Article Resistance of livestock to viruses: mechanisms and strategie...
John Leif Jan-Erik Karlsson
This article is also interesting:
Article Detection of genomic regions underlying resistance to gastro...
- Badges
- Science topic
- Similar topics
- Clinical Pharmacology
- Dosing