Coat Colour. Lakeland Terrier

Transcription

1 A Discussion of Coat Colour Genetics in the Lakeland Terrier Chapter 2 Dog Hair By Ron Punter Page

2 Representation of section of an active hair follicle Topcoat hair The surface Epidermis is confluent with the follicle outer sheath Undercoat hair Sebaceous Gland unit Inner Root Sheath Bulge Erector pili muscle Pheromone Gland Germinal Matrix Bulb Dermal Papilla R Punter Page 2

3 Dog Hair is very different to human hair. Being a frugal sort of a chap, as a teenager, I discovered that mixing together the residue in part used paint cans, whatever the colours going into the amalgamation, always produced brown. Regardless of its precise shade I always refer to it as Sunset Brown. Fifty plus years experience of mixing now -just finished painting a Ginny Pig hutch in a lightish shade which with the addition of more white could easily become Dishwater Blond. Human hair is often Sunset Brown produced by varying proportions of pheomelanin and eumelanin mixed in the hair shafts. Dog s hair colour genes don t generally mix pigment in that way but keep different pigment to separate areas. Again speaking from personal experience some of us are born a shade of Blond but disappointingly as we mature it gradually changes to Sunset Brown, again that doesn t happen with dogs. Lakeland s are double coated. The undercoat is woolly. The top coat hairs Tip Drawing depicting blown hair, plucked from follicle (magnified) Base tend to be stiff -what is known as Wire Hair, a dominant trait that cannot be breed by mating two soft coated dogs together. The undercoat is the same basic colour genetically as the top coat in any particular area of the dog but in the Lakeland it often develops more poorly pigmented and hence lighter in shade. A Hair is not a living substance it is a layered strand of solidified Keratin protein The living organ that produces hair is the follicle buried deep into the skin; the bulb at the bottom of the follicle grows the keratin protein and adds to the length of hair from the base. Melanin producing cells add pigment into it. The hair is continually pushed up the follicle inner sheath as it grows. Once grown from the follicle it cannot change colour biologically though environmental factors such as bleaching by sun light may affect it. In contrast to hair, skin is a living substance and contains Melanin producing cells which are stimulated by sunlight to produce more pigment. Human follicles just have a single hair but the dog Page 3

4 has compound follicles with a main guard hair and numbers of softer hairs (undercoat) all coming out of the same follicle opening in the skin. Sebaceous glands secrete an oily/waxy substance called sebum to lubricate and waterproof the skin and hair, Lakelands tend not to be as greasy as some other Terriers. Cuticle Cortex Medula Hair Shaft Cross Section the skin surface, Lakelands have a fairly flat coat. My drawing provides a key to some major features of the follicle: If the follicle aperture is oval the hair will be crimped and tend to have a rather attractive wave. The hair stands up in response to hormones tensioning the arrector pili muscle. That s when we say he s got his hackles up. The normal stand of the hair is determined by the angle of the follicle shaft to Hair is shed when the follicle enters a resting period known as the Telogen stage of hair growth when the dermal papilla withdraws from the base of the follicle. The growing stage is called Anagen in humans this can last up to seven years for a particular follicle and adults shed only a few hair at any one time. Dogs follicles are more synchronized though Lakelands tend not to moult as such because the follicles linger in the intermediate Catagen phase and add thin unpigmented length to the hair that s when we say the coat is blown. Pulling out human hair is not advisable as it will damage the follicle but in Lakelands stripping out the hair stimulates new stronger, better pigmented growth and is how Lakelands are kept in trim. Although external hair is not living it doses transmit movement to the follicle nerve sensors at its base which gives the impression that hair has feeling Page 4

5 which brings us on to the very stiff Whiskers. Most dogs on a mission to explore a narrow opening ignore the signals from the whiskers connecting sensors and Lakelands are particularly insensitive in this regard but not if they are being groomed and whiskers should never be plucked. The subsidiary follicles start to develop when the pup is a couple of months old and by three months undercoat will be apparent - there will be two to five accessory hairs accompanying each primary hair. Although my drawing just shows a couple of associated follicles, by six months old there are five to fifteen woolly hairs grouped round each guard hair. Ultimately there are between 100 and 300 bundles of hair per square centimeter of coat. Lakelands might tend to a lower number compared to say Welsh Terriers which often have much denser coats (but there could be other reasons.) That density indicates just how thin a hair is on our scale of things and because the width of hair is about at the limit of our vision it is often used as a comparator for smallness ( thin as a human hair ) but on a molecular scale the width of a hair is about equivalent to a million (1,000,000) carbon atoms and hair is a complex micro structure. Wool hairs have no, or just a small, central Medulla. Though present in guard hairs this region is relatively unimportant generally consisting of fairly soft keratin. The main part of hair is the Cortex, it has a complex structure and determines all the main characteristics of hair and contains the pigment. In undercoat the cortex is not as densely packed with dead keratinised cells as wire guard hairs are. The outer protective covering is the hair Cuticle consisting of layers of overlapping more or less transparent scales. Dogs don't lose much water due to sweating and certainly not by the Aporcrine sweat gland which makes for a complete misnomer as they are in fact merocrine. These glands secrete pheromones which it is thought give every dog an individual odour signal that is recognisable by other dogs. It s often said that new hair follicles cannot be grown on scar tissue but this is not strictly correct - stem cells can completely regenerate follicles at a wound site and when this happens the first hair will come in the colour of a new born puppy and then go through whatever development changes are inherited (de novo regeneration). Page 5

6 Pigment Pigmented cells contain Melanin granules. Mammals can have two forms of melanin in their coats. Black, Eumelanin, which can also appear brown/liver or blue-gray when affected by the dilution genes or greying. The second pigment is Yellow, Pheomelanin, which is very variable from pale cream through shades of yellow, tan and red. Page 6