FE mys­te­ri­ously af­fects NZ, but nowhere else

NZ Lifestyle Block - - Country Smile -

In the late 1930s, fa­cial eczema was decimating sheep flocks in the greater Waikato, with farmers reg­u­larly los­ing 1000 sheep each year, es­pe­cially hoggets. The dry coastal hill coun­try from Port Waikato down to Raglan was es­pe­cially hard hit.

Things got so bad that Fed­er­ated Farmers de­manded that re­search be started to find the cause and a cure. The govern­ment re­sponded and Dr CP Mcmeekan moved from Massey Col­lege to start a new An­i­mal Re­search Sta­tion at Ruakura.

The an­swer would take 30 long years to find. The break­through came when the grounds­man at Claude­lands in Hamil­ton no­ticed black dust on his boots when mow­ing the grass. That dust turned out to be the fun­gal spores of Pithomyces char­tarum which was shown to pro­duce the toxin sporidesmin.

Few could be­lieve that a fun­gus could be the cause, when so much time and money was spent in­ves­ti­gat­ing all sorts of other daft sug­ges­tions and quack cures which MAF was com­mit­ted to test­ing.

This fun­gus is present in other coun­tries, but the spores are not toxic any­where else. Why they would be so dam­ag­ing in NZ con­di­tions has never been ex­plained. It was a pity that so much en­ergy was wasted by Ruakura sci­en­tists ar­gu­ing with Te Aroha farmer and for­mer den­tal nurse, Gla­dys Reid. She dis­cov­ered zinc was the best preven­tion for the liver da­m­age caused by FE back in the late 1940s, thanks to her work in the den­tal in­dus­try and years of re­search. Gla­dys would throw zinc salts into farm water troughs, even test­ing her live­stock by dos­ing some and not oth­ers to check her (cor­rect) hy­poth­e­sis.

While farmers in NZ and the USA fol­lowed her lead and raved about her work, the Ruakura team never liked it and a point­less ar­gu­ment over who was first to ‘dis­cover zinc’ went on for 30 years. Be­fore Gla­dys died in her 90s in 2006, I got her to put a col­lec­tion of her pa­pers in the Hamil­ton City Li­brary archive. Gla­dys al­ways be­lieved that she was awarded her OBE to pla­cate her over the way MAF had treated her. What Ruakura did do was iso­late the best zinc dose rates which was very im­por­tant work as too much zinc can be toxic and dam­ages the ru­men.

Zinc ox­ide was used as a drench, which was easy for dairy farmers as cows al­most opened their mouths when they saw the drench gun. But it was a dis­as­ter for sheep farmers who had to mix the pow­der and water in the wool­shed (an old wash­ing ma­chine was good) and dose them twice a week. The whole place and the staff would get cov­ered in the stuff.

Zinc could also be put into the water trough, but it had to be zinc sul­phate, and there was al­ways the prob­lem of con­trol­ling the amount in­di­vid­ual an­i­mals were drink­ing.

In the late 1970s the team at Ruakura came up with a bo­lus to solve the prob­lem. This could be ad­min­is­tered by mouth and would last in the ru­men for about a month be­fore the an­i­mal needed an­other one. Some sheep farmers started notic­ing that af­ter the dec­i­ma­tion of their flocks, there were al­ways some sheep that sur­vived to keep on per­form­ing. Two drivers of

the be­lief that there must be a ge­netic com­po­nent were farm ad­vi­sor (and for­mer All Black cap­tain) Andy Dal­ton and his col­league, the late Colin Southey.

They be­lieved some stock were ge­net­i­cally more re­sis­tant to FE. To test this con­cept, Ruakura staff started by breed­ing a line of highly-re­sis­tant sheep, a line of low-re­sis­tant sheep, and a con­trol line. These lines were formed by drench­ing sheep with the sporidesmin toxin har­vested from fungi at Ruakura, then mea­sur­ing the ef­fect on the liver us­ing a GGT test de­vel­oped in hu­man medicine to check the state of the liv­ers of al­co­holics. Spec­tac­u­lar progress was made in both di­rec­tions of se­lec­tion, prov­ing FE re­sis­tance (or tol­er­ance) had a clear ge­netic base.

This led Colin Southey to de­mand that toxin drench­ing be­fore se­lect­ing rams was made avail­able to farmers in his area, and flocks have now been on that pro­gramme (called Ram­guard) for over 40 years, with spec­tac­u­lar re­sults. Com­mer­cial farmers buy tested rams and their genes flow through the flock to spread the re­sis­tance genes. Some farmers who have spe­cialised in test­ing for the long­est pe­riod to guar­an­tee their sheep have now de­vel­oped the re­cent ‘Fe­gold’ brand.

Breed­ing cat­tle for FE re­sis­tance has been sadly ne­glected, even though re­search at Ruakura some years ago showed the trait in cat­tle was also some­thing ge­net­i­cally in­her­ited. Dairy breed­ing or­gan­i­sa­tions have been slow to recog­nise that half the calves born are males reared for beef, and drench­ing them for FE as they grow large is a chore that beef farmers and small block own­ers want to avoid. FE spores are easy to see down a mi­cro­scope, look­ing like tiny brown hand grenades. Early on, staff at Ruakura de­vel­oped a ‘wash method’: they would cut a sam­ple of grass and dead lit­ter at the pas­ture base, mix it with water in a jar, shake it, then count the spores from a drop of it on a spe­cial cal­i­brated slide. This is still the way it’s done by vet clin­ics, and kits can be pur­chased for farmers to use them­selves.

It’s the young, rapidly-grow­ing spores that pro­duce the toxin. Old dead spores that look black and solid down the mi­cro­scope are harm­less.

The trou­ble with spores is that their num­bers are not con­sis­tent over a whole farm, or even in the same parts of the pad­dock. Counts are high in shel­tered ar­eas and on dif­fer­ent types of slope, de­pend­ing on sun­shine. If you are go­ing to count spores, then sam­ple dif­fer­ent ar­eas of the farm or you risk er­rors by re­ly­ing en­tirely on a gen­eral spore count. When spore counts are down in the low hun­dreds and con­di­tions are cold, cur­rent wis­dom is that there’s no prob­lem un­til there’s a spike of say a mil­lion spores/g of grass. This usu­ally oc­curs when rain ar­rives af­ter a long dry spell in the warm hu­mid days of late sum­mer and early au­tumn. But it’s im­por­tant to re­alise that dan­ger can start with a se­ries of low counts be­cause an an­i­mal’s liver be­comes sen­si­tised. It means when a high level of tox­i­c­ity is reached, it doesn’t take a very big spore count to have a re­ally dan­ger­ous ef­fect, and the level of pro­tec­tion the an­i­mals have been given will not be enough for ef­fec­tive pro­tec­tion. It quickly be­comes a cri­sis which needs ur­gent ac­tion, but by that stage it may be too late. Get­ting min­er­als into the liver is like charg­ing a bat­tery. It takes at least three weeks af­ter the start of zinc treat­ment for it to be ef­fec­tive, and this is al­ways a prob­lem for a lot of peo­ple as you need to start dos­ing stock on 1 Jan­uary. In some places now, even this may not be early enough as FE cases are be­ing found be­fore Christ­mas.

Ad­min­is­ter­ing zinc is a chore that many farmers hate, but don’t de­lay things un­til you hear about spore counts ris­ing on some other lo­cal farms.

On small blocks, to ad­min­is­ter a bo­lus – your best bet – you’ll need some good yards, prefer­ably a head bail, and you’ll need to get an ex­pe­ri­enced per­son to do it so that the bo­lus stays in the ru­men and no dan­ger is done to man and beast. That often means bring­ing in your vet.

When to end zinc treat­ment is get­ting trick­ier with cat­tle as long pe­ri­ods of zinc treat­ment are needed right into May as sea­sons stay warmer for longer. But pro­longed zinc treat­ment is known to strip cop­per from the liver, so vet­eri­nary ad­vice is needed on this one, to work out how much cop­per is needed. This is not an is­sue with sheep. Spray­ing the whole farm or se­lected ar­eas is still rec­om­mended, and can be an easy

op­tion. But again, know­ing how ef­fec­tive it has been will mean you need reg­u­lar spore count­ing to keep an eye on things, and it may not be to­tally ef­fec­tive if there is a mas­sive spike of spores, when zinc drench­ing will also be needed.

Fun­gal spores end up on and in the soil, so there is ad­vice around about how a fer­tiliser pro­gramme can af­fect spore num­bers and re­duce the risks of FE. Sci­en­tific opin­ion varies on this claim, but plenty of farmers who have ap­plied lime and used fer­tilis­ers high in trace el­e­ments can claim not to have had FE in their stock. It is worth study­ing for fu­ture man­age­ment to avoid all the work and cost of an­i­mal treat­ment. Sheep suf­fer more than cat­tle as their eyes and ears swell. They then rub them un­til they are red-raw, and un­til they can­not see. You won’t see great lay­ers of skin come off as you do in cat­tle. Sun­shine drives stock mad as it must in­crease the itch­ing.

Newspapers in English

Newspapers from New Zealand

© PressReader. All rights reserved.