In 1986, Dr Leyden Baker and colleagues at Ruakura Research Station evaluated the inheritance of foot and jaw abnormalities in ewes.
Five traits were scored on each individual foot on some 2250 Romney, Coopworth cross Romney and Border Leicester cross Romney ewes at nine months, 18 months and again at five years of age.
The five foot traits scored were foot placement (straight-, pigeon- or splay-footed), toe placement (straight, crossed or spread), foot roll (straight, or rolled inwards or outwards), pastern angle (straight or angled) and hoof growth (hoof wall length that would require trimming or not).
At the time of foot-trait scoring, the distance between the front teeth and the front tip of the dental pad (whether undershot or overshot) was also measured. All ewes remained in the flock for the duration of the trial.
As nine-month hoggets, the heritabilities for all foot traits except hoof wall growth were low. That is, only a small proportion of the observed variation in the foot traits was genetic in origin.
At 18-months and again at five years of age, the heritabilities for all foot traits were low to moderate. The heritabilities for undershot or overshot teeth were also low to moderate.
Additionally, all foot and teeth traits recorded at nine or 18-months of age were poorly correlated with the hogget traits of weaning weight, 12- and 18-month weight and fleece weight. The same applied for the foot and teeth traits recorded at 18-months or five years of age in relation to ewe weights, fleece weight and numbers of lambs born or weaned.
So, what do these results tell us in practice? Hoof wall growth and to some extent teeth placement appear to have some medium-level genetic component, accounting for say 20-30% of the variation observed. In contrast, genetics accounts for probably less than 20% of the variation seen in the other foot traits.
Functionality gives us the confidence that our animals will move freely around the hills and get the job done.
The fact that teeth and some foot conditions in ewes (and rams) have some moderate expression in a flock is not necessarily a valid reason for culling. If available, information on productive-trait EBVs indicating future flock productivity should be taken more into account than minor variations in teeth or foot structure.
When individual EBV information isn’t available – for example, in the commercial ewe flock – excessive attention to minor deviations in foot and teeth structure is unwarranted since they’re a part of the natural variation that exists in any flock. Certainly major deviants from this norm would warrant culling but they should only make up a very small proportion of the flock.
Let’s face it, if there was a strong genetic component to these functional traits, previous generations of breeders and farmers would’ve removed these animals from their flocks and we wouldn’t have the structural faults we seem to be culling for still. Maybe our perception of functionality needs to be reconsidered.
Functionality gives us the confidence that our animals will move freely around the hills and get the job done. When looking at our animals then perhaps we should adopt a mindset of the retention of functional “soundness”, accepting a small range of natural variation rather than looking for and culling all possible functional “faults”.
• Dr Geoff Nicoll was head of Landcorp’s Genetics Unit for nearly 40 years before retiring in 2013. He is now director of Geoff Nicoll Genetics.
