Wireworm-resistant – Majobe merinos

Merino breeder Johan Hoffman of Bothaville in the Free State has virtually eradicated wireworm (Haemonchus contortus) from his 800-strong stud flock. He spoke to Annelie Coleman.

Wireworm-resistant – Majobe merinos
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Johan Hoffman nearly lost his stud Merino breeding flock due to wireworm infestation. Johan runs the Majobe Merino stud on the farm Vlaklaagte near Bothaville in the Free State with his wife Marie-Louise and their son Jos. The Hoffmans started breeding stud Merinos 15 years ago and Johan recalls the wireworm infestation. “Sheep died in heaps. We turned the situation around by introducing the Famacha (Faffa Malan Chart) system developed by specialist sheep vet Dr Faffa Malan and a team from the University of Pretoria.”

The system compares the colour of the mucus membrane of a sheep’s lower eyelid, a reflection of the degree of anaemia, to a standard colour-based ‘eye score’ card to determine the degree of wireworm infestation, and the level of treatment required. “Because we only treat infected sheep, it prevents the worms from developing resistance to anthelminthic drugs,” explains Johan.

In summer, sheep are kept in 1ha and 2ha dryland lucerne camps in an intensive grazing system, and in winter they are run mainly on maize stover. “We plant maize in a precision production system,” says Johan. “Sheep thrive on stover and the fact that the animals are able to pick up maize kernels is an added bonus.

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“In summer, the flock is kept in more than 52 small dryland lucerne camps and rotated every six to eight days, depending on the condition of the grazing. Our stocking rate is between 10 ewes/ ha and 15 ewes/ha on the lucerne. Grazing is rotated in six- to eight-week cycles, depending on the rain.”

Johan Hoffman says that one of the biggest mistakes he made was buying rams on visual clues alone, without taking BLUP values into consideration.

Breeding selection
Because of long-term selection, the Majobe flock has wireworm-resistant and resilient sheep. Animals resistant to wireworm will naturally destroy a certain number of parasites in the stomach, having evolved this ability in a similar fashion to game animals. Sheep with resilience can survive and produce despite having high parasite loads. According to Johan, the Majobe stud probably has better wireworm resistance and resilience than most other Merino studs in the country.

The Hoffmans culled sheep that stayed infected after three bi-weekly drenches. It was soon clear that certain genetic lines, particularly ram lines, were naturally more prone to wireworm infections. All mass-drenching was stopped in 1998 and individual sheep were treated according to their Famacha ratings. “This was the tipping point for our business,” recalls Johan. “Profitability increased as mortality and input costs decreased. However, although it was a breakthrough, it could not be scientifically quantified until Dr Jan van Wyk from the University of Pretoria started trials on the farm two years ago.”

The basic trial plan involved 100 sheep on the same pasture. A monthly drench trial group was compared with a targeted, selectively treated (TST) group. This group was dewormed on an as-need basis calculated on clinical signs according to Bath and Van Wyk’s (2009) five-point check system. This consists of nasal examination, conjunctival (ocular mucous membrane) colour, presence or absence of sub-mandibular oedema (water under the jaw), body condition score and diarrhoea score.

In terms of weight, research results indicated that in the Majobe stud case, the differences between the ‘drench’ group and the ‘TST’ group were relatively small and there were no significant differences in production. The following aspects were considered: animal handling and labour involved in monthly drenching, the cost of about R5/ animal for anthelminthic treatment, and the possible consequence of drug resistance.

Famacha system
“Twenty of the ewes in the trial flock were drenched monthly with a new product. By implementing the Famacha system, we started selecting for wireworm resistance and resilience. After each inspection, infected animals were treated,” says Johan. “Two weeks later, those still affected were treated a second time. These animals were re-examined after another two weeks. Those that remained infected were culled. “That’s how we built our flock over the years. The University of Pretoria’s trials validated our selection criteria and confirmed our sheep are wireworm-resistant and resilient.”

Through the use of ocular mucous membrane examinations, the Hoffmans have found that many sheep with extremely high wireworm egg counts can still function optimally. “Breeders often rely only on faecal samplings from a small proportion of a flock. They then treat the entire flock when only some animals have high worm egg counts. “By blanket-treating all animals when a few show signs of wireworm, it’s impossible to select individuals with superior ability to withstand worm challenge. Certain individuals can cope well with faecal egg counts of 20 000/g or more,” explains Johan.

Jos and Marie-Louise record lamb weights. Records are kept up to date so that BLUP values can be established.

Dung beetles
Another disadvantage of blanket-drenching is that the drugs are excreted in the dung, which affects dung beetle populations. These beetles play help to limit the survival of worm and fly eggs as well as larvae in manure. Lambs are treated for wireworm and tapeworm at weaning. Ewes, especially multi-birth ewes, are examined during high rainfall months from January to March and only infected animals are treated.

“We’ve contained wireworm to such an extent that we’ve virtually done away with drenching,” says Johan. “We drenched only one ewe that gave birth to triplets during the March lambing season this year. The only disadvantage of our system is that one has to eyeball the animals and during stressful times the flock has to be inspected fortnightly.

“Training in the application of the Famacha system is essential to learn how to apply it and what its limitations are. It’s only applicable to blood-sucking endoparasites.” He believes the Famacha system ultimately ensures long-term sustainable animal health, resulting in optimum profitability through increased production.

Breeding strategy
Johan follows a staggered breeding strategy and 50% of the flock are mated every eight months. The rams are kept with the ewes for 34 days and the ram-ewe ratio is one ram to 40 ewes. About half of the flock is artificially inseminated and AI genetics are selected according to BLUP. An average birth weight of 4,9kg is maintained and average weaner weight is 22,4kg. The mean inter-lambing period is 262 days, with a weaner percentage of 185% and the mean lambing percentage is 201%.

Johan is a strong advocate of scientific livestock farming practices and keeps his records up to date so that detailed BLUP values can be established. The Majobe flock is regularly inoculated against blue tongue, pasteurella and Rift
Valley fever. To combat the threats of predation and stock theft, the flock is kraaled at night. Licks and supplemental feeding are specifically designed according to the recommendations of an animal nutritionist.

Contact Johan Hoffman on 082 455 8871 or [email protected].