Hormones and Moulting

Animals living in seasonally changing environments must accurately time yearly events, like migration, moult, hibernation and reproduction in order to survive, and successfully rear their young. Animals resident in highly seasonal environments with short growing seasons are more likely to evolve seasonal phenotypes than conspecifics whose niches provide more evenly distributed food resources throughout the year (Concannon et al 2009). In some cases these events occur in direct response to seasonal changes in the external environment such as alteration in ambient temperature or day length.  This adaptive reactive strategy allows the necessary physiological changes to occur rapidly.  In many instances physiological adaptations need to begin well in advance of the environmental change.  This means there will be for many mammals an internal seasonal adaptation, that is; they occur in the absence of changes in environmental time and are endogenously generated (Thrun et al 1995).

In most vertebrates, neuroendocrine functions are organized in regular cycles of different periodicity, which may range from minutes to months. Cycles of approximately 12 months are known as circannual rhythms, while periods of approximately 24 h are called circadian rhythms. Cycles that occur more frequently than once daily are termed ultradian  cycles (Johnsonn 2009).
The seasonal adaptation is controlled by the biological pacemaker, but it can be difficult to distinguish between externally and internally regulated rhythms.  However, if the animal  is isolated and deprived of all external signals including the daylight variations that can provide time information,  and the physiological rhythm then shows a period deviating from the 24 hour cycle it is possible to conclude that the rhythm is internally controlled (Johnsonn 2009; Mustonen2003 ).
Seasonal changes in photoperiod adjust the period duration of circannual cycles, which is typically 9–10 months under constant conditions, to 365 days. Thus, the expression of circannual rhythms involves an interaction between an endogenously generated signal and environmental cues  (Duncan 2007 ).

Hormones serve as a mechanism for mediating seasonal changes in physiology.  Two photo-dependent hormones are Prolactin and Melatonin. Prolactin is synthesised in the anterior pituitary gland but also in the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviours and it  plays a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role (Freeman  et al 2000). Melatonin is primarily synthesised in the pineal gland. Prolactin and melatonin have a synergistic effect, the melatonin secretion pattern is an inverse function of day length, and circulating melatonin levels correlate inversely with Prolactin levels. Melatonin secretion occurs during the hours of darkness, so the amount of melatonin biosynthesis is directly related to the length of the daily dark period. The quantity continues to increase in autumn until winter solstice (Mandel 2012).

Most studies on circannual rhythms in mammals is done on humans or wild animals, there are very few of the domestic dog, however studies that have been done,  have shown a circannual rhythm which shows seasonal fluctuations in line with wild and human studies ( Kreeger et al 1992; Corrida et a 2003; Gobella et al 2002).

Mink exhibit a seasonal fur growth cycle regulated by photoperiod. As the length of the photoperiod decreases; an increase in melatonin concentration and a decrease in Prolactin results.  Which initiate growth of the winter pelage, which begins in September in northern latitudes. In spring, the opposite occurs: the length of the photoperiod increases, resulting in an increase in Prolactin concentration and a decrease in melatonin, initiating the spring moult (Valtonen 1995). Mink treated with implants of melatonin in June, when natural melatonin production is low; are exposed to an artificial melatonin they have suppressed Prolactin production and exhibit an early onset of autumn moult and produce prime winter pelage 6 to 8 weeks earlier than normal (Rose 1984).

Belyaev (1979) demonstrated a destabilizing effect on the loss of strict circannual rhythm through the domestication process.   Food generalists like the domesticated pet dog that exploit diverse diets, and generally are kept sheltered from the weather tend to be less subject to seasonal pressures than specialists reliant on a few seasonally variable foods (Concannon et al 2009.  But despite that domestic dogs do moult in autumn and develop a winter a coat, and they have been shown to have a circannual rhythm.  It seems likely that the increasing endogenous melatonin secretion after the summer solstice triggers the autumn moult of the domestic dog .

Therefore the start of the winter coat in domestic dogs will begin after the summer solstice predicting the oncoming winter, due to the decrease of Prolactin as a result of increased melatonin secretion.

References
Belyaev, D. 1979. Destablising selection as a factor in domestication Journal of Heredity (1979) Vol 70 No 301 pp 301-308.

Concannon, P Castracane v. Temple, M Montanez, A. (2009) Endocrine control of ovarian function in dogs and other carnivores Animal  Reproduction., 178 v.6, n.1, p.172-193, Jan./Mar. 2009

Corrada, Y. Castex,G. Sosa,Y. Gobello, C. (2003) Secretory Patterns of Prolactin in Dogs: Circannual and Ultradian Rhythms Reproduction in Domestic Animals Volume 38, Issue 3, pages 219–223, June 2003

Duncan, M (2007) Circannual prolactin rhythms: calendar-like timer revealed in the pituitary gland TRENDS In Endocrinology and Metabolism Vol.18 No.7 August
2007.

Freeman,M.  Kanyicska , B.   Lerant, A. Nagy, G. (2002)  Prolactin: Structure, Function, and Regulation of Secretion Physiological Reviews Published 10 January 2000 Vol. 80no. 1523-1631 Avaliable from: http://physrev.physiology.org/content/80/4/1523>

 Gobello,C.  Corrada,Y  Castex,G . de la Sota, R and  Goya R (2002) Secretory patterns of growth hormone in dogs: circannual, circadian, and ultradian rhythms Canadian  Journal of  Veterinary Research. Apr 2002; 66(2): 108–111.

Johnsonn A. 2008. Light, circadian and circannual rhythms in Solar Radiation and Human Health .Espen Bjertness, editor. Oslo: The Norwegian Academy of Science and Letters, 2008. Available from: http://www.dnva.no/geomed/solarpdf/Nr_5_Johnsson.pdf

Kreeger,T. Seal,U. (1992)  Circannual prolactin rhythm in intact dogs housed outdoors.  Chroniobiologia (1992), Vol 19(1-2): pp1-8.


Mandel, F(2012). Textbook of Animal Behaviour Second edition PHI Learning Private Limited, New Delhi.

Mustonen, A. (2003). Seasonality, photoperiod and nutritional status in the control of endocrinological weight- regulation. – University of Joensuu, PhD Dissertations in Biology, n:o 18. ISSN 1457-2486

Thrun,L. Moenter,S. O’callaghan,D. Woodfill,C. Karcsh,F. (1995) Circannaula Alteranions in the circadian rhythm of melatonin secretion. Journal of biological rhythms Vol 10 March 1995 pp42-54.


Valtonen M, Vakkuri P, Blomsted L:  (1995) Autumnal timing of photoperiodic manipulation via melatonin to winter pelage development in mink. Journal of Animal  Science 61:589, 1995.

Your needs; the dogs needs; a simple formula to alter the behaviour of your dog, and your relationship with the dog.

Diagram: an adaptation of Maslow’s hierarchy of needs (1943)

According to Maslow  (1943) all  human beings have a hierarchy of needs, it is displayed as a pyramid and before an individual can go up in the pyramid each need needs to be fulfilled, The first part is physiological needs this is the need of survival:  the need to breathe; have food and water;  able to excrete;  sleep; and  the need to procreate. After all these needs are met  individuals  go up in the triangle to the next level; which is safety needs, in order to feel safe there is a need for good health, all resources readily available to sustain physiological needs like: warmth; a place to live; stability, cleanliness; safety within the family; and a role within the family.  Once these needs are met and sustained ‘beings’ progress up another level to  love and belonging : love from the family; relationships;  and a sense of belonging and sexual intimacy; once these needs are met further progress to the next level esteem : here individuals seek self-esteem; confidence; achievement and respect, fun and play.  After the esteem needs have been met  you progress to self-actualization  which means fulfillment, where you reach for your actual potential this is a constant process, and provided that all the needs in the lower levels are being met you constantly strive to develop.

The dog has the same needs as you, in the wild a dog will seek his needs himself and a domestic dog will seek to satisfy his own needs, so in order to prevent the dog seeking satisfaction that might not fit in within  the  family home it best to provide those needs.  Just providing those needs can prevent bad behaviour developing or even eliminate  a behaviour that is undesirable. On the whole a bad behaviour develops not because it is wrong in the dogs mind but that need has not been provided by the owner.

If you provide a dog with food, water, a place to excrete,  and allow them to sleep, and not get to hot or cold the dog will survive.  So having given the dog a chance to survive you need to provide the dog with his safety needs, in order for the dog to feel safe he needs to know that all of his physiological needs will always be fulfilled, your need to ensure he is in good health, a safe place to live and sleep, warmth, stability, his role within the family is safe.

It does not take much for a dogs feeling of safety to be undone. A move of house, a new member of the family,  a change in routine, a new dog or cat, even a new dog moving in to house up the road can threaten the dogs feeling of safety.

Once the dogs physiological and safety needs are met they progress to love and belonging, all dogs have a need to belong whether it is within a pack of dogs or within the family home, a building of relationships is very important for good behaviour.  It is at this point that  If you have an entire dog or bitch and their need for procreation is not fulfilled the dog is going to have difficulties progressing to the next level of need, its not impossible but there might be a  certain amount of frustration and distraction. 

So now you have a dog that is surviving, feels safe, and has a sense of belonging, the dog then needs his esteem addressed. Ensuring that the first three levels are sustained will give the dog confidence, however life is unpredictable and there confidence can be quickly dented.  This can be overcome by ensuring that the dog  makes achievements, this is when training comes into its own.  Each new skill a dog learns boosts his self esteem, the more he learns the more tools he has at his disposal to deal with the unpredictably of life and ensuring that his confidence carries on developing.  A dog is a dog and needs to do dog things for his own esteem;  to smell the air, feel  freedom, run, play,  and chase. At this level bad behaviour is replaced by good behaviour.

Now the dog that was just surviving, is now safe, feels that he belongs, he is confident with a high self esteem, he is now ready to embark on the journey of fulfillment whereby he can maximize his potential, with the support of his owner. The journey is only just beginning.