Rat-Tail Syndrome (RTS) in Highlands
What RTS Looks Like
It is a syndrome of mis-shaped, curly and sparse hair coat over the body, and, of note, an absence of switch tail hair (the long hairs on the tip of the tail), giving rise to the name – “rat tail” syndrome.
As can been seen in the images below, the short, curly coat & lack of tail hair, appears to improve as the animal gets older. Of note, is that the RTS gene only affects pigmented hairs (not white hairs), and so the dun Highland steer with “frosting” (see more on frosting or the mahogany coat colour) in the images in this article, has a tail switch as an adult, because these hairs on the tip of his tail are white.
Images of a suspected RTS Highland
(** Suspected because of the look / phenotype, although there is no commercially available specific genetic test for RTS currently. **)
Problems Associated with RTS
It appears to be mostly cosmetic. The syndrome in Highland cattle does not appear to cause any physical, performance or reproductive problems, although research suggests that there are problems with thermoregulation, and so RTS cattle may struggle a bit more in extremes of temperature – eg one research paper showed reduced weight gains post-weaning in winter. (2)
The Most Likely Genetics of RTS in Highland Cattle
An autosomal additive model of inheritance for RTS is suggested (1). Of note with this particular syndrome in Highlands is that it is only seen in dun animals (ie black animals with one dilution gene). The RTS gene appears to be dominant, but can be present in Highlands but not manifested (a carrier), if they are any other colour than dun.
There appears to be 3 genes that work together (1) to have a rat-tail animal exhibit the disorder. They are:
- “E-Locus” – >1 black gene (ED/-) (on BTA18 chromosome)
- “D-locus” – only one dilution gene (Dc/-) (on BTA5 chromosme)
- “RTS locus” – > 1 RTS gene (RTS/-) (on BTA5 chromosome – but a different location to the D-locus above)
The interaction of these 3 genes is known as epistaxis, which means “when at least two different genes interact together to affect the same trait”.
Not to be confused with ……
As well as the RTS gene identified in the most recent paper on the topic (2), there appears to be at least two other genes that are reported to be responsible for variations in hair length or structure that can appear very similar to RTS (1). This syndrome is known as Congenital Hypotrichosis.
* HEPHL1 gene on BTA29, reported in Belted Galloways.
* KRT71 gene on BTA5, reported in Herefords with a dilution gene on their base red colour, inherited in a recessive mode.
Congenital hypotrichosis, is an inherited disorder that can look very essentially the same as RTS in Highland cattle (calves are born without much hair, and then grow a sparse hair coat that is short and curly).