Gene marker test pioneers

BREEDING FOR footrot resistance has the potential to save sheep producers up to 11m a year, with just one round of selection having the potential to save £2.7m.

Footrot costs UK flocks £24m a year, so breeding footrot-tolerant sheep could yield huge financial and welfare benefits, reckons MLC geneticist Gert Nieuwhof.

“A breeding programme will not initially lead to a reduced prevalence, but it can reduce the costs of treatment and lost performance – with an estimated saving of about £11m a year.”

Breeding footrot-resistant sheep depends on being able to identify tolerant sheep. A genetic marker test developed in New Zealand and commercially available there since 2000 allows such sheep to be identified, says its creator, Jon Hickford, of Lincoln University, Christchurch.

“On one farm that has been using footrot tolerance as a selection criteria for rams for the past four years, the costs of footrot control have fallen by nearly 75%, with Footvax and antibiotics no longer needed. The time spent trimming feet has also fallen by a similar amount.”

Despite these reductions, Dr Hickford says this flock is only in a footrot control phase and will save more in future. “The producer is confident that after another four years of similar action and one particularly dry year, it will be possible to eradicate footrot entirely from the flock.”

The genetic marker test works by assessing the level of immune response a sheep will direct at the footrot-causing bacteria. It does this by identifying which particular copy (allele) of a gene related to footrot tolerance a sheep is carrying, he explains. “So far, 30 alleles have been found, but we only test for 18 of these as we are confident that the other 12 are of little relevance.”

Sheep are then ranked according to their level of footrot tolerance on a scale of 1-5, with one being the most tolerant and five the least tolerant. “Sheep receive two scores, recognising that they inherit genetic material from both parents and can pass either version of the gene to their offspring.”

A typical score from the test would be shown as 2, 4, demonstrating that one side of the allele is relatively footrot tolerant, while the other is highly susceptible. “The best possible score would be 1, 1, and the worst is 5, 5. But all combinations in between are possible.

“While the test does not guarantee sheep will be footrot resistant or free, it does allow better genetics to be used in flocks that will in time impart greater tolerance to footrot.”

Progeny tests using rams with known footrot tolerance status on ewes with unknown status have borne out the test results. The most resistant rams sire progeny with high levels of footrot tolerance, explains Dr Hickford (see table).

However, he cautions against selecting for footrot resistance at the expense of other traits. “Breeding solely for footrot-tolerant sheep could compromise other traits. Breeders must not lose sight of the main purpose of their breeding programme, whatever that may be.”

While Dr Hickford is confident the test will be available in the UK shortly, he does have concerns about its use without UK validation. “I’m fairly confident we won’t find any different genotypes in UK sheep because most New Zealand breeds are based on UK breeds. But the different production systems may mean the technology has to be used in different ways.”

It is also possible the test will need updating in future years as the footrot bacteria may mutate to be able to affect tolerant sheep. “When the bacteria comes under severe challenge of survival, it will find a way out of the situation.”

But having developed one test it should be relatively simple to develop another to cope with future mutations, he adds.

With any selection process the greatest benefits will come through the maternal breeds, reckons Dr Nieuwhof. “These breeds will have the greatest influence as they are the foundation stock for the industry.”

In the UK, Hamphsire Down breeder Mike Adams is keen to make use of the test. “Having visited a farm in New Zealand that has been using it, I am convinced it will benefit the UK industry and is worth spending time and money on.”

Mr Adams has yet to make use of the test, but he has semen in store from a ram tested in New Zealand. “We hope to use this semen this year and will see how his lambs perform in relation to foorot,” he adds.