The horse’s coat is a useful indicator of its health. Depending on the time of year and grooming, a healthy horse will have shiny coat. A young, well nourished and active horse will have a naturally shiny coat whilst older horses and those with ailments such as Cushings may have a longer and less shiny coat. Draft types generally have a coarser and less shine coat at any age and of course in winter all horses’ coats become fluffy and less shiny.
There are those times when our pals shed their lovely smooth, glossy coats in favour of their fluffy, winter ones or exchange their fluff for a lightweight summer version. That time of year when everything is covered with a covering of short hairs. It’s on your clothes, in your hair and eyes and in your mouth!
The clocks went forward last month and temperatures are rising. Adagio started losing her coat a couple of weeks ago and I have always assumed that it was to do with temperature. I was wrong. Actually it’s about the number of daylight hours.
It was not obvious to me how the coat can be affected by the number of daylight hours. This is how it works. Eyes contain photosensitive ganglion cells which send information about the amount of daylight to a gland called the pineal gland which is in the centre of the brain. This gland produces melatonin. Melatonin is a hormone that regulates other hormones and maintains the body’s circadian rhythm (an internal 24 hour “clock”) which anticipates the daily onset of darkness and affects reproduction behaviour, coat growth and camouflage colouring as well as sleep patterns. This physiological reaction is known as photoperiodism.
There is plenty of information about why and when a horse will shed its coat but how does the body know whether to grow a winter coat or a spring coat? I haven’t been able to discover any data on this. So putting two and two together I believe that the final length of the hair shaft is determined by both the rate of hair growth and the duration of the active growth phase (anagen) of hair follicles. Increased melatonin production in the lengthening autumnal nights generates a longer anagen phase so hairs grow faster and for a longer period than in the spring when evenings are shortening and days are lighter. Ambient temperature has only a slight influence of the length of the coat.
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