Developing a genetic test for footrot
Footrot is a disease that costs New Zealand sheep farmers over $80 million a year to treat. Selective breeding using a Footrot Gene-Marker Test (FGMT) could significantly reduce the amount of footrot on farms.
What is footrot?
Footrot is a contagious disease affecting ruminants, especially sheep. It is caused by a bacterial infection in the hoofs of the animal, causing swelling, redness, decay and pain in the foot and eventually causing lameness.
At its worst, footrot can cause an infected hoof to fall off. Infected sheep will also lose weight, wool quality decreases, and the sheep become more susceptible to other infections. Sheep may die from the disease or be culled by the farmer.
Fine-wool breeds such as merino and mid-micron are particularly prone to footrot.
The bacterium that causes footrot in sheep is called Dichelobacter nodosus, or D. nodosus for short. Footrot is more common when the weather is warm and wet, as the D. nodosus bacteria thrive in these conditions.
Collecting the data
In 2004, Glen Greer from Lincoln University undertook a study to find out more about the costs of footrot to the sheep-farming community and the impact that the FGMT was having on it.
Glen collected her data by carrying out case studies of two of the first farms in the FGMT programme, interviewing 11 stud ram breeders using FGMT and by means of a postal survey of the 2,200 merino and mid-micron sheep farms in New Zealand. There was about a 50% response rate to this survey. She then did a postal survey of all of the stud ram breeders using FGMT (there were 76). 48 sent back valid responses
The cost of footrot on fine-wool sheep farms
More than half of the merino and mid-micron sheep farms surveyed had experienced footrot. 35.5% of merino sheep farms and 33.8% of the mid-micron sheep farms had problems with it in every year. Traditional footrot treatment and prevention for the average merino costs $0.78/year, while for the average mid-micron sheep it costs $0.48/year.
However, costs can get as high as $4.93/merino sheep/year and $3.09/mid-micron sheep/year on badly affected farms.
On top of this, farmers suffer a loss in production (wool, sheep and lambs). Loss of production due to footrot is estimated to cost merino farmers $0.99/sheep/year and mid-micron farmers $0.50/sheep/year.
Animal welfare is also of prime concern to sheep farmers. Footrot is a debilitating disease that causes much suffering.
It is also time consuming and unpleasant to treat. Footrot therefore causes much distress amongst the sheep-farming community. Almost 80% of surveyed farmers consider footrot to be one of the top three threats to animal health on their farm. (The other consistently highly ranked threat was gut parasites.)
What is the Footrot Gene-Marker Test (FGMT)?
Cost of footrot
The cost of footrot on New Zealand sheep farms.
In 1997, Dr Jon Hickford and a team of researchers at Lincoln University isolated a gene that was linked to susceptibility to footrot. This gene has at least 26 different alleles, each related to different levels of susceptibility or resistance. The scientists used their discovery to develop the Footrot Gene-Marker Test (FGMT) for use on farms.
The farmer makes a tiny nick on the sheep’s ear, collects a dab of blood on a piece of card, and sends it off to Lincoln University. There, the DNA is extracted from the blood and analysed to identify the particular allele combination present in that sheep. The farmer is sent back a score between 1 and 5, with 1 and 2 indicating high resistance, and 4 and 5 signalling high susceptibility.
Because sheep carry two copies of each gene (i.e. two alleles), they get two scores. Either one of these alleles could be passed on to each offspring, and so a sheep with a score of 2/2 might be a better breeding sheep to have in your flock that a sheep with a score of 1/5. The sheep with a 2/2 score will pass on pretty good resistance to footrot to all their lambs. The sheep with a score of 1/5 will have a 50% chance of passing on the allele for footrot susceptibility to each lamb.
Read more about Genes involved in footrot: Patterns of inheritance.
The FGMT programme
The FGMT programme was established in 2001. New Zealand was the first country to trial this technology. It uses the FGMT to identify rams with high genetic resistance to footrot. The aim of the project is to selectively breed stud rams with high resistance to footrot so that, in time, fewer sheep will suffer from the disease. This could potentially lead to a reduction in costs to the farmer and an increase in farm productivity.
The first farmers to join the programme were ones who were having huge problems with footrot on their farms. For some, the problem was so bad that they were planning to stop farming sheep with fine wool. They were very keen to find a less drastic solution to their problem.
Funding for the programme was supplied by MAF’s Sustainable Farming Fund, MerinoNZ Inc. and Mid-Micron Wool NZ Inc.
What impact is the FGMT having?
A third of the sheep farmers who used FGMT results when selecting their breeding rams had seen a reduction in footrot on their farm. These tended to be the farmers who had previously had a high incidence of footrot, and consequently high related costs.
Farmers that have seen a significant impact from the FGMT breeding programme estimate that it has reduced their footrot-related costs by between 50% and 80% and increased production by 60% to 80%. For example, where footrot was costing $4.93/merino sheep/year it dropped to $2.02/merino sheep/year. Where it was costing $3.09/mid-micron sheep/year it dropped to $0.73/mid-micron sheep/year.
The other two thirds of farmers reported seeing no significant impact of the FGMT programme on the rate of footrot on their farms. This could be because they did not use the FGMT results when selecting their rams, or because footrot was less common during the three years of the programme even in farms that were not using FGMT. This could have been due to drier weather. Therefore there has been no significant difference in the decrease of cases of footrot on farms breeding footrot resistant sheep and those that are not. This is a bit like trying to see who is the better tennis player – you or Roger Federer? – without giving either of you tennis racquets.
Ram breeders still see FMGT as being a useful tool and one that their customers, the sheep farmers, will grow to appreciate more and more as they begin to see the benefits in action on their farms. This may not happen until a change in recent weather patterns brings on more warm, wet weather and the incidence of footrot rises again.
The research
This research was carried out by Glen Greer of Lincoln University's Agribusiness and Economics Research Unit, (AERU), in order to report to the Sustainable Farming Fund managers about the impacts that FGMT is having on sheep farming in New Zealand. The Sustainable Farming Fund supplied funding for the FGMT programme, read this report here.
