CLEARDALE IS ONE OF THE TOP PERFORMING FLOCKS FOR FOOTROT RESISTANCE IN NEW ZEALAND.
ASBV FOR SUSCEPTIBILITY TO FOOTROT (FR) - TRAIT DEFINITION
The trait ‘susceptibility to footrot’ is quoted as FR.
FR describes a sheep’s susceptibility to footrot using it’s genetic difference in footrot score.
This score measures how well a sheep retains foot health under a challenge with virulent footrot.
What do the numbers mean?
The less susceptible a sheep is to footrot, the lower it’s FR ASBV is.
ASBVs for FR are reported as the weighted average foot score deviation from the FR NZ research database baseline (which is 0).
For example; an animal with a FR ASBV of -0.4 has a weighted average footrot score 0.4 of a score lower than the database baseline. A ram with an ASBV of -0.4 for FR will pass half of his genetics onto his progeny, which will be -0.2 of a weighted average footrot score less affected.
Susceptibility to footrot is moderately heritable (approximately 25%) meaning that a substantial proportion of the trait variation is explained by genetics.
How is it measured?
Sheep get footrot if they are genetically susceptible and exposed to virulent forms of the footrot bacteria. If the conditions are right the bacteria first infects the skin between the claws before progressing from the interdigital skin and soft horn to underrun the sole of the foot and ultimately to the hoof wall. When a footrot disease challenge has progressed enough to differentiate between unaffected and affected animals, the mob can be scored for footrot.
All four of a sheep’s feet are scored on a six-point scale from 0 - 5, with score 0 being an unaffected foot and score 5 being a foot with severe footrot progressed to the entire foot.
Sheep can only be inspected during an active, virulent outbreak of footrot when the disease is spreading and is not residual chronic untreated footrot from a previous outbreak. Therefore scores are only collected from young sheep (age 6 months – 2 years of age) in large mobs. Older sheep may have been infected and treated before.
Before foot score data is accepted by Sheep Genetics to estimate the ASBV for FR, the following challenge thresholds must first be met (for score definitions refer to figure 1 ‘Foot scores (0-5 scale)’ below):
1. 10% of animals have at least one foot that is score 3 or greater
2. 50% of animals have at least one foot that is score 2 or greater
Feet are scored at the appropriate stage of the footrot challenge and by an accredited footrot scorer.
For complete information on how you can challenge and have an accredited foot scorer score your stud sheep, contact Sheep Genetics at firstname.lastname@example.org or Footrot Breeding Value Project lead, Dr. Mark Ferguson at email@example.com.