Neuroendocrine regulation of maternal behaviour in dogs

Table of Contents

1.0 Abstract
2.0 Introduction
2.1 Maternal behaviour and examples
2.2 Hormonal influence on maternal behaviour
2.3 Milk production and secretion
2.4 Comparison of maternal behaviour in altricial species vs precocial species
2.5 Abnormal maternal behaviour
3.0 Conclusion
4.0 Bilbiography
4.1 Other Referenced Materials
4.2 Figures

1.0 Abstract

This paper examines how the regulation of maternal dogs’ neuroendocrine system can affect their behaviour. Maternal behaviour in dogs is portrayed by licking, grooming, nursing and behavioural correction. Keywords that were used include; maternal, behaviour, hormonal, neuroendocrine, dog, milk, secretion, altricial, precocial, abnormal, puppies. During this paper we discuss basic maternal behaviours and sample, the hormonal influence of behaviour, milk production and secretion, the comparison of maternal behaviour in altricial species vs precocial species and abnormal maternal behaviours found in dogs. We were able to conclude that the neuroendocrine system heavily affects the behaviours portrayed, with the main hormones being prolactin, oxytocin and progesterone.

2.0 Introduction

The link between the brain and endocrine systems in the control of maternal behaviour has become a topic of scientific interest in recent years. In animals, certain hormones, neurochemicals, and brain areas have been linked to the induction, maintenance, and retention of maternal care. These chemical processes and anatomical substrates are examined in relation to development and the reproductive life history of female mammals.

The actions of hormones from the pituitary and other peripheral endocrine tissues play a crucial role in feeding back upon sites within the central nervous system, many within the hypothalamus, to regulate the female's responses to young and related stimuli as we will discuss within this paper. As a result, maternal behaviour control is as much an endocrine neurological process as it is a solely neuroendocrine mediated one. The goal of this paper is to describe the existing framework of the underlying neuroendocrine basis in maternal behaviour control and we will hope to achieve this by providing surrounding information to show a fair and well informed correlation between the topics.

2.1 Maternal behaviour and examples

Maternal behaviour is defined as “the collection of behaviours by the mother that can increase offspring survival” by (Krasnegore and Bridges, 1990). This behaviour starts when the bitch delivers her litter at the stage known as parturition and these mannerisms will usually continue until the puppies have been weaned off the mother. There have been studies and research to show the effect of the mothers maternal care in the pups during their first years has shown impact on the wellbeing and behaviour in the future. This becomes an important interest to dog breedings in an attempt to cut these unfavourable behaviours out. The most commonly observed behaviours include licking, grooming, nursing and behavioural correction. These mannerisms aid the bonding between the mother and her offspring and also play a key role in the survival and protection of the puppies due to the fact that during the first few weeks they have very little movement and are born deaf and blind so rely on the mothers care for development.

When puppies are born they are usually born surrounded by the amniotic sac and if they are not released from this quickly after birth they will die from asphyxiation. Naturally this is the bitches role to break the foetal membrane and will then proceed to lick both the mouth and the head of her puppies in order to stimulate respiration. Anogenital licking are observed shortly after birth and are essential during the first 3 weeks of life to stimulate urination and defecation in puppies, this was shown by (Scott and Fuller, 1965). The frequency of the licking is seen to decline slowly over time and after around 3 weeks the puppies should be able to urinate and defecate without the stimulation from the mother.

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Figure 1 (a)The bitch, provides warmth and protection to the puppy and stays with it most of the time. (b) The bitch nuges the puppy with the snout to mammary glands to facilitate its nursing. (c) Since the puppy fails to move around by itself, the bitch helps it by gently grabbing the neck of the puppy to move it

Feeding and nursing of the puppies plays a large role in the interaction between the mother and her offspring. The physiology behind nursing is due to hormonal influxes and the CNS which will adapt to the needs of the puppies and will generally decrease over time as the puppies rely less frequently on the nursing. During the first 3 weeks the suckling is initiated by the bitch, the puppies will latch to the nipple and the duration of the nursing is regulated by the pups themselves who will simply delatch from the nipple once they are fed.

The maternal behaviour during the first few weeks postpartum will alter the hypothalamic-pituitary-adrenal axis or stress responsiveness pathways of the neonates, and will continue to change during the development and ageing of the offspring. For example in a study conducted by (Guardini et al, 2016) proved the link between the behaviour of the puppies at 2 months and the amount of maternal care provided by the bitch and concluded that there was a correlation showing the influence of care on the coping strategies of the puppies at a later stage. It also showed that there is a huge environmental impact of adaptation to new environments and socialisation with humans as well as lower levels of anxiety and fear.

2.2 Hormonal influence on maternal behaviour

The exact factors that play a role in the onset of maternal behaviour in dogs is still unknown. However it has been thoroughly studied in rodents (Numan, 2012) which has provided a further insight into some of the hormones that play a vital role in encouraging maternal instincts both during and after the birth. Studies show that the blood concentration of oestrogen and prolactin increases during pregnancy. The combined increased production of these two hormones causes the medial preoptic area (MPOA) in the hypothalamus to become active which inhibits the mothers antisocial defence circuit and recognises the offspring as her own. One study showed the significant importance of prolactin in preparing for delivery, lactation and after care of the litter. The study used inhibitors to prevent the use of prolactin during the pregnancy which allowed researchers to prove the hormone's role in maternal behaviour.

Oxytocin is another one of the main hormones that is credited with encouraging maternal behaviour specifically in the first twenty-one days postpartum. Oxytocin is secreted by the posterior pituitary gland and is stimulated by one of two events; Ferguson’s reflex and suckling stimuli. Ferguson’s reflex occurs due to the sudden increase of pressure in the cervix caused by the crowning of the puppies head. This also causes the concentrations of estradiol and progesterone to increase further building a stronger maternal instinct in the mother. The suckling stimuli is caused by the puppies drinking from the mammary glands.

Dopamine is the most well researched neurotransmitter linked in maternal care in animals. Research has been held which have proved the positive correlation between increased dopamine concentrations and increased mother-pup interactions. As well as the decrease in interactions between the mother and pups when dopamine concentrations were decreased. These finds would strongly argue that the hormone Dopamine does have a positive effect on maternal behaviour in dogs.

A prominent hormone during pregnancy is progesterone. The highest blood concentration occurs mid pregnancy but it is vital from implantation through till birth. During the pregnancy, progesterone prevents preterm contractions. However, progesterone concentrations in the plasma have to decrease in order for labour to be induced. Following this decrease, concentration of prostaglandin F2 increases which further results in an increase of oxytocin in the mother. These hormones encourage the mother to portray nesting habits in preparation of labour.

Immediately after birth the mother will secrete a pheromone from her breast area known as Dog Appeasing Pheromones (DAP) . This supplies the puppies with the sensation of calm and comfort and in turn encourages the pups to nurse.

2.3 Milk production and secretion

In the last stage of pregnancy mammary epithelial cells convert into active sensory cells to allow the process of lactogenesis to occur. Lactogenesis is the initiation of milk secretion. Colostrum, which is the first secretion from the mammary glands after giving birth that is rich in antibodies, is produced and accumulated in the alveoli before parturition. Galactopoesis is the continued production of milk, and it is dependent on appropriate udder emptying. Both the transformation of epithelial cells into secretory cells and the continued production of milk require hormonal signals. The main hormones that have a role in regulating lactogenesis are Prolactin, Oestrogen, Progesterone and Cortisol

Prolactin concentration increases significantly during the final stage of pregnancy, in some mammals as much as a 5-10 fold increase is recorded before birth. Prolactin is a hormone responsible for binding to receptors located on the surface of epithelial cells. This generates a response resulting in the synthesis of secondary messengers which in turn increases the transcription of mRNA molecules used to code for milk proteins such as casein. Prolactin also is involved in the production of α-lactalbumin which is secreted from the mother via the milk to the offspring.

The maintenance of the metabolic apparatus in epithelial cells is regulated by a hormone called Oestrogen. Studies show that cows that were given a treatment of Oestrogen combined with Progesterone, milk production is increased by 70% only after seven days. It is suggested that the oestrogen most likely causes a slight increase in the production and secretion of Prolactin which further results in mammary cells being converted into active sensory cells and milk production beginning.

Around the time of childbirth there is an increase in the concentration of Cortisol in the plasma. Cortisol is responsible for the growth and the differentiation of the rough endoplasmic reticulum (RER) and the Golgi apparatus. Both of these organelles are involved in not only the synthesis of mammary epithelial cells but also the secretion. Competitive inhibition occurs between Cortisol and Progesterone for receptor proteins. However, Cortisol becomes significantly more effective after birth due to the sharp decrease in concentration of Progesterone that occurs before labour.

2.4 Comparison of maternal behaviour in altricial species vs precocial species

Altricial is defined as “being hatched or born having young that are hatched or born in a very immature and helpless condition so as to require care for some time”. Examples of altricial species include birds such as owls,herons, woodpeckers and mammals such as dogs, cats and primates such as humans. They are usually unable to move on their own and therefore rely on the mother during the first few stages. The ability to survive and grow in the environment they are introduced to is reliant on the maturation of the vital organs at birth. Some neonates may require the mother to feed them or hatch. Behaviours of altricial species included building nests for the birth of their offspring to protect them as they will have limited movement.

Precocial species are “those in which the young are relatively mature and mobile from the moment of birth and hatching”. Examples of precocial species include horses, ducks, deer. Due to being more mature from birth they thus require less maternal care and can usually feed themselves or forage for their food whilst still being nursed by their mothers. In contrast to the altricial species their organs are far more developed meaning they can keep vital functions independently such as thermoregulation. In reviewed data (Scheiber et al, 2016) showed that maternal behaviour is less intense in precocial species than in altricial ones.

2.5 Abnormal maternal behaviour

The main issues with maternal behaviour include aggression, cannibalism, rejection and pseudocyesis. Aggression in bitches postpartum is usually only temporary and should pass when the puppies get older as they need to protect their offspring from potential threats entering the nest. There is a link between the changes related to lactation and the bitches ability to perceive possible threats. Aggression may also be caused by an underlying issue such as mastitis. Cronyism is the state in which the bitch consumes the offspring after killing them. It is an uncommon trait but the bitch may be trying to reduce the little quantity or to destroy any offspring that has come out defected or dead. There are biological factors that may impact the lack of maternal behaviour such as oxytocin and blood lipid levels being lower than they should be. In an experiment conducted and investigated by (Kockaya et al, 2018) they measured the oxytocin levels of 15 bitches with cannibalistic traits and 15 without from the same breed. The results of the experiment show a substantially lower level of oxytocin in those who had the cannibalistic trait as well as a lower level of cholesterol. This led the researchers to conclude that oxytocin is thus an essential neuroendocrine factor in bitches to develop maternal behaviour.

Some bitches may fail their maternal duties and leave their offspring without providing the warmth, nutrition and care to help them urinate and defecate. This rejection may be caused by issues with the pregnancy and the removal of the pups away from the mother and holding them. If the mother only rejects one or two of the puppies it may be due the mother thinking the puppy is not good as it may be too cold and thus rejecting it. However, if the bitch rejects the whole litter this may indicate a medical issue with the bitch and this will need special attention. If this is the bitches first little she may be anxious and this may cause her to reject a little however when she has another litter later she should be a good mother.

Pseudocyesis is the condition which involves a non-pregnant bitch experiencing the same hormonal changes as a pregnant bitch would undergo. This condition is caused by a rise in prolactin concentration when the progesterone levels drop and this triggers the mammary development, producing milk and displaying maternal behavioural mannerism. This may include mothering of inanimate objects or a rise in aggression levels. This also causes swelling in the mammary gland the same as it would in a pregnant bitch.

3.0 Conclusion

The behaviour of maternal dogs both before and after delivery is influenced by neuroendocrine regulation. The hormones oxytocin, prolactin, and progesterone are thought to have the most impact on behaviour, albeit each has a somewhat different effect and outcome on the mother. We've gone over the most frequent and anticipated forms of maternal dog behaviour, as well as some unusual deviant behaviours. There is still a lot more study that needs to be done on this topic in order to prove a more accurate link between regulation and maternal behaviour. If this research was expanded upon, it could help breeders identify features that should be avoided and the methods they could aid in the deterrence during the critical stages with the mother and her pups

4.0 Bibliography

4.1 Other Referenced materials

4.2 Figures

  1. (Photo MVZ Gibran Olivera Rodríguez) (CC BY 4.0)

maternal_behavior_dog (last edited 2022-05-15 08:59:43 by IstvanToth)