Genetic gains help cut sheep worm resistance

Having selected sheep for parasite resistance, Richard Chantler has reduced anthelmintic use by half.


One of the UK’s leading New Zealand Romney breeders, who is making significant progress towards worm resistance in his flock, says breeders may soon be in a position to sell certificated sheep with a given level of resistance.

Richard Chantler says research scientists in New Zealand are close to identifying the genes for worm resistance.

“I believe it won’t be long before we will be able to sell certificated sheep with a given level of resistance, be that single copy or double,” says Mr Chantler who, with his wife, Penny, runs a flock of 300 pure-bred New Zealand Romneys at Hill Farm, Llanigon, Hay-on-Wye.

Worm resistance has been a priority as the Chantlers have developed their flock, using semen from Murray Rohloff’s Awereka stud in the South Island. For the past 15 years this New Zealander has been breeding for worm resistance.

Mr Chantler selects sheep for their parasite resistance. By collecting sheep droppings, he has successfully reduced by half the reliance on anthelmintics for internal parasites. This year, the average worm count a sheep has dropped from about 800 eggs/g of faeces to 200 eggs/g.

“We believe drenching sheep is an unnecessary chore,” he says. “Drench resistance is too common around the world; drugs are becoming unpopular and it is harder to find new ones.

“When we first started on the worm-resistance trail we hadn’t drenched any adult sheep for 15 years, we just culled the daggy ones. We were already doing regular worm counting with our own Fecpak on-farm faecal egg count kit, so going a couple of steps further wasn’t a problem.”

His protocol is to mob-count, then drench before carrying out another mob count. He expects a clean result and then repeats the mob count every five days until the result is up to 800 eggs/g. He then takes individual samples, with repeat samples eight days later.

At this point, the two samples accrue to allow a FEC Effective Breeding Value to be calculated. “When we started five years ago we only got about six ram lambs with a minus FEC, but now the best 10% are minus 35%. In fact, we only drenched the lambs in 2009 for the FEC protocol,” says Mr Chantler.

The Chantlers established the flock in 1986 when they bought ewes from the Wye College Romney Development Group. These were high fecundity “Kent” Romneys and New Zealand Romneys. Two years later they inseminated the ewes with semen from the New Zealand Romney Development Group, using a ram with the highest score for fecundity. With 3m ewes in the Group at that time the genetic base was large. The Chantlers were also impressed with the effort the Kiwis had put into genetics and selection.

The ewes are mated using the Animate selection programme, which matches ewes to selected rams for specific traits without the risk of inbreeding.

This allows the Chantlers to make even faster genetic gains for selected traits, including worm resistance, weaning percentage, growth rate, carcass quality and wool. “I still believe wool is worth it,” says Mr Chantler. “Only once has wool not at least paid for the shearing and we shear twice a year, in May and October.”

The sheep graze off-farm on winter tack between October and March. If there is no grass when the ewes return for lambing, they are fed cake and hay. At 1100ft, grass growth doesn’t kick in until the end of April.

The triplets are mostly lambed inside, but left as triplets so they can be looked after as well as possible. “We want them to prove they can rear three,” says Mr Chantler.

He tries to keep all rams and shearlings away until May. “By then we have enough grass to feed 300 ewes, their lambs and the shearlings, so no sheep sold as breeding stock has had anything to eat but grass,” he says. “By managing the youngstock this way they are fit not fat. Our rams regularly serve 150 ewes and keep growing.”

All ram lambs are kept entire for recording and only when the results come back in October does he cull about half of them.

These are finished either on keep or in a shed after Christmas. The top 50% of the ewe lambs are kept either as replacements or to sell as shearlings.