TO WormMail mailing list (recip. undisclosed)
WRML.20120726.why lambing ewes are susceptible to worm infection (periparturient relaxation of resistance) – REDUX 2 (Kahn, Leathwick and Karlsson
‘Some more information, this time from John Karlsson (Western Australia). This wraps up these WormMails (three) on this topic for now.
For information on Rylington Merinos and selection for worm resistance, see: http://www.agric.wa.gov.au/PC_91868.html?s=0
Rylington Park is located in the Western Australian Shire of Boyup Brook
. – SL.
A few comments from a winter rainfall environment based on ‘Rylington Merino’ (Australia’s most worm resistant Merino flock).
1. A. R. Williams, J. C. Greeff, P. E. Vercoe, R. J. Dobson and L. J. E. Karlsson (2010) Merino ewes bred for parasite resistance reduce larval
contamination onto pasture during the peri-parturient period. Animal 4:1
, pp 122–127.
This reports on; host and parasite genotype effect, fecundity effects, in a set stocking environment.
2. J. Greeff, L Karlsson and Noreen Underwood (2006) BREEDING MERINO SHEEP FOR WORM RESISTANCE INCREASES
PROFIT IN A MEDITERRANEAN ENVIRONMENT. 8th World Congress on Genetics Applied to Livestock Production, August 13-18, 2006, Belo Horizonte, MG, Brasil
This paper follows the progeny of the ewes reported on in Williams et al. above through to hogget age and is one of the first effort to derive an economic value of resistance to worms and a lower periparturient rise.
3. K.E. Kemper, D.G. Palmer, S.M. Liu, J.C. Greeff, S.C. Bishop, L.J.E. Karlsson (2010) Reduction of faecal worm egg count, worm numbers and worm fecundity in sheep selected for worm resistance following artificial infection with Teladorsagia circumcincta and Trichostrongylus colubriformis. Veterinary Parasitology 171
This paper is also based on the Rylington sheep but using males and artificial challenge in a pen trial. Again shows both host and parasite genotype effects. It also shows important parasite species differences in their ability in coping with the host immune response with Teladorsagia in the best position to exploit a suppression of the host immune response.
4. S. M. Liu, T. L. Smith, D. G. Palmer, L. J. E. Karlsson, R. B. Besier and J. C. Greeff (2005) Biochemical differences in Merino sheep selected for resistance against gastro-intestinal nematodes and genetic and nutritional effects on faecal worm egg output. Animal Science 81:
This paper as the title describes looks at biochemical differences in the sheep referred to by Kemper et al above. The relevance to this discussion is that under immune challenge there is a strong demand from the immune system for the sulphur-containing amino acids and they are also in high demand from wool production. This may explain some of the apparent differences in the periparturient rise comparing the Merino and NZ sheep.
John K jkarlsson[AT]agric[dot]wa[dot]gov[dot]au "
Previous two WormMails on this topic follow:
Monday, 16 July 2012 1:42 PM
Subject: WRML. why lambing ewes are susceptible to worm infection (periparturient relaxation of resistance) – REDUX (Kahn and Leathwick)
To WormMail mailing list (recip. undisclosed). WRML.20120716.why lambing ewes are susceptible to worm infection (periparturient relaxation of resistance) – REDUX (Kahn and Leathwick)
Further to the WormMail of 6 July [ https://wormmailinthecloud.wordpress.com/2012/07/06/wrml-why-lambing-ewes-are-susceptible-to-worm-infection/
], with Dr Lewis Kahn’s article on periparturient relaxation of resistance (P(P)RR), here are some further comments from Dr David Leathwick of Palmerston North, New Zealand and Dr Lewis Kahn of Armidale, NSW, Australia.
Comments from D Leathwick (Agresearch, Palmerston North, NZ)
Steve, I would like to point out that the situation below (see article of 6 July below)
only applies (I believe) to Merinos.
This issue was raised some years ago when we proposed, based on modelling, that anthelmintic treatments to ewes around lambing would significantly increase selection for resistance.
When the equivalent drenching scenarios were run through the Australian Wormworld (computer)model by Ian Barger, the answers were quite different. Ian’s conclusion was that the different outputs from the models was a direct reflection of the assumptions regarding the relaxation of immunity around lambing – the Australian model (for Merinos) used a large and protracted loss of immunity until late in lactation, while the New Zealand model (Romneys) allowed for only a very limited relaxation of immunity in the weeks either side of lambing.
This story can be found in:
Barger I.A. Models as a guide to sustainable worm control. Chapter 16 in Barrell G.K. (Ed.) Sustainable control of internal parasites of ruminants. Animal Industries Workshop, June 1997, Lincoln University, Canterbury NZ, 203-213.
We subsequently measured the establishment of challenge infection in Romney ewes after lambing and found that establishment rates, although relaxed for a short interval, returned to low levels (<1%) within a few weeks of lambing – this can be found in:
Leathwick D.M., Miller C.M., Brown A.E. & Sutherland I.A. 1999. The establishment rate of Ostertagia circumcincta and Trichostrongylus colubriformis in lactating Romney ewes. International Journal for Parasitology 29: 315-320.
Not surprisingly this results in a different picture of worm dynamics than that described below (L Kahn’s article
We subsequently tested the model hypothesis that drenching ewes pre- or post-lambing would accelerate the development of resistance in a 5 year field trial, which showed that the hypothesis was true for Ostertagia, T. colubriformis and H. contortus, thereby supporting the structure of the model. See:
Leathwick DM, Miller CM, Atkinson DS, Haack NA, Alexander RA, Oliver A-M, Waghorn TS, Potter JF, Sutherland IA. 2006 Drenching adult ewes: Implications of anthelmintic treatments pre- and post-lambing on the development of anthelmintic resistance. New Zealand Veterinary Journal 54 (6): 297-304
Anyway, I think you should clarify that the description of immunity relaxation outlined below is unlikely to represent all countries and/or breeds of sheep; it is certainly not the case in New Zealand.
Response from L Kahn (UNE, Armidale, Australia)
Hi Steve and Dave,
Thanks Dave for your email which is very timely as we are just embarking on some new work with crossbred (Border Leicester (BL) x Merino (Mer)) ewes and so I have been thinking about breed differences in worm resistance.
When writing the article for WormBoss
I did indeed have Merino ewes in mind and I should have made comment that the Merino represents the most extreme example of the loss of immunity at parturition and during lactation. Having said that, loss of immunity associated with reproduction has also been reported in other species (pig, cow, mouse, etc) and so the periparturient effect has some general basis. I did not have a copy of your research note and this very nicely contrasts the situation with your Romney ewes and what has been reported for Merinos. It is interesting that an early report on the PPR came from Romney ewes:
Brunsdon R.V. (1964) The seasonal variations in the nematode egg counts of sheep: a comparison of the spring rise phenomenon in breeding and unmated ewes. New Zealand Veterinary Journal 12:75-80.
We are expecting our BL x Mer ewes to be more worm resistant than Merino ewes (Donald A.D., Morley F.H.W., Waller P.J., Axelsen A., Dobson R.J., Donnelly J.R. (1982) Effects of reproduction, genotype and anthelmintic treatment of ewes on Ostertagia spp. populations. International Journal for Parasitology 12:403-411
), but as few BL studs in Australia place any emphasis on worm resistance, and because there is still 50% Merino, we are also expecting considerable within-cross variation. We are only just starting with the new project but already we have recorded worm egg count values in BL x Mer ewes comparable to the range that we would expect for Merino sheep.
On the matter of linkage between host resistance and drench resistance: even though I was writing principally about susceptible Merino ewes, we too are concerned about the potential for pre-lambing treatments to select more strongly for drench resistance (whereas Barger et al were not). In our case, where lambing typically comes in Spring and at a time of year where L3 on pasture are at a low point (and made lower through deliberate management in the previous Autumn) I suspect that the effect of the pre-lambing drench may be more similar to the situation of a resistant breed, where there are few incoming L3 to address the selective bias in favour of resistant worms. In our case we look to manage this potential through within-farm quarantine practice at weaning (see more below-Ed.
) as part of the drench choice annual strategy.
I also have an obvious eye to management of H. contortus evident in the WormBoss article and Steve has already (thank you) clarified this with readers.
As an aside, one of the things I find intriguing from Brunsdon’s work is that the relaxation of immunity seems to be specific to some species. The best example for us (in NZ) would be Nematodirus which is extremely rare in the PPR (periparturient relaxation of resistance). Also the intestinal Trichostrongylus sp occur but are less dominant than Trichostrongylus axei, yet in lambs it is the reverse.
I agree that the species specific nature of the PPR (periparturient relaxation of resistance) is intriguing. For example, there are reports that the rise in Haemonchus contortus WEC with lambing is due principally to increased fecundity but we have demonstrated high establishment rates of incoming Haemonchus contortus 3rd
stage larvae (L3) – in Merino sheep.
Some extra comments and notes:
"within-farm quarantine practice at weaning": this has been included in the revamp of WormBoss, of which Lewis Kahn of course is a part. Essentially this entails treating lambs and ewes when they leave the lambing paddock (usually at weaning) with an effective short acting drench or combination of drenches unrelated to that which was used as a pre-lambing drench (if one was used). So, if a macrocyclic lactone drench was used pre-lambing, the ‘quarantine’ drench at weaning to ewes and lambs (weaners) might be, for example, an organophosphate-based combination (if highly effective on the property).
The other part of the strategy is to then dilute the ‘resistant’ worms’ left behind on the lambing paddock post-weaning. Most people assume this means putting cattle into the lambing paddock post-weaning to reduce numbers of sheep worm larvae. But, while this will reduce overall numbers, the proportions of resistant and susceptible worms will remain the same. The better option then is to put into the lambing paddock relatively wormy sheep that preferably were not last/recently drenched with the same or related drench active that was given to ewes pre-lambing. After a period during which resistant worms on pasture are ‘diluted’, then cattle can be put into the paddock to reduce numbers of sheep worm larvae.
‘lambing times’ Spring is indeed a common lambing time in much of Australia, not least in the summer rainfall zone of north eastern NSW and SE Queensland where Haemonchus (and haemonchosis) is endemic. However autumn and early winter lambing is also frequently encountered in other sheep raising areas for various reasons. In some districts, spring and autumn lambing can both be common.
Haemonchus contortus: barber’s pole worm
Trichostrongylus spp. (intestinal species): black scour worm. Trichostrongylus axei: stomach hair worm
Ostertagia (Teladorsagia) circumcincta: (small) brown stomach worm.
‘Low worm-risk paddocks’: clearly this is relative. You might also call them ‘clean paddocks’ which could be misleading, especially as a ‘clean’ paddock in say the New England region of NSW in a wet summer has many more worm larvae on it than say a cereal stubble in December in parts of Western Australia or the Riverina of NSW.
Can we infer that Australians are generally more relaxed than their uptight cousins across the Tasman ? 🙂
John Cleese and Palmerston North
Somehow, I don’t think Cleese is smarting at all.
The WormMail of 6 July:
Subject: WRML: why lambing ewes are susceptible to worm infection
To: WormMail list (recip. undisclosed) WRML.20120706. why lambing ewes are susceptible to worm infection
immunity, Kahn, lambing ewes, periparturient relaxation of resistance (PPRR), sheep, worms, McClure, WormBoss redevelopment
WormMails have been a bit thin on the ground of late as I have been tied up with other things.
By way of recompense, here is a nice article on ‘PPRR’ by Lewis Kahn, a nice follow on from Dr Sue McClure’s article on immunity.(See here: https://wormmailinthecloud.wordpress.com/2012/06/06/wrml-sheep-immunity-to-worms-mcclure/
Some of you have had the good sense to subscribe to WormBoss Monthly News, and would have seen this article there in the June issue:
The article is republished here with permission.
"Why are lambing ewes susceptible to worm infection?
Dr Lewis Kahn, Associate Professor, Animal Science, University of New England, Armidale NSW, Australia
Adult sheep typically have reasonable levels of immunity to most types of round worm with their greatest struggle often being immunity against barber’s pole worm. A reasonable level of immunity will mean that no more than 5% of infective larvae are able to establish as adult worms in the sheep. For the lambing ewe, this situation starts to change as early as three weeks before lambing when ewes start to lose immunity. Loss of immunity gets continually worse over the next 8-12 weeks (until lamb marking or a little after) which makes lambing ewes highly susceptible to worm infection. Ewes that rear twin lambs suffer an even greater loss of immunity.
During this time 30-40% of infective larvae can establish as adult worms causing high worm egg counts in the ewes, lower milk production and higher worm challenge for lambs.
Over the years a number of reasons have been put forward to account for the loss of immunity in the lambing ewe. Research has demonstrated that rather than hormonal changes associated with lambing and lactation it is the supply of protein and energy that is most important for maintaining immunity. The energy and protein requirement of the lambing ewes increases two and threefold respectively in the 4 week period between lambing and peak milk production. It is common for increased requirements to outstrip the supply of energy and protein from pasture and the gap contributes to a loss of immunity. The larger the gap the bigger the loss of immunity and this explains why twin-rearing ewes are much more susceptible to worm infection.
The most effective ways to manage worm infection in lambing ewes are to ensure ewes have:
1.low worm egg count (by conducting a WormTest) prior to lambing or receive an effective drench;
2.access to low worm-risk paddocks which have not been contaminated with infected faeces for 2-5 months (shorter for warmer months and longer for colder months) prior to lambing;
3.increased genetic worm resistance by using worm resistant sires in a breeding program;
4.achieved target condition score 3 for lambing."
The times mentioned above (2-5 months) relate particularly to barber’s pole worm (Haemonchus contortus) and the New England region of NSW.
‘WormTest’ is faecal worm egg counts (with or without larval culture/differentiation (‘worm type’)).
‘Infected faeces’ in point 2 above refers of course to faeces containing sheep worm eggs. i.e. grazing with cattle, for example, is not excluded.
By the way, WormBoss is undergoing redevelopment, part of which involves a new and better WormBoss website. ‘Shouldn’t be too long now…..