Prenatal development and in utero influences

The influence of the environment on behavior may actually come into play even before birth. While studies in dogs are limited, there are many studies in other species such as humans, rodents, and production animal species to suggest that the in utero environment is important for puppy development. Many studies in humans support the effect of prenatal stress on cognition and behavioral fearfulness in human infants.^2,3 The importance of neurodevelopmental influences on the mental and emotional well-being of children is a subject of intensive review.^4–6 The influence of experiential, biological, and genetic factors on the developmental variation in fearfulness and anxiety in humans during infancy and early childhood has been explored based on animal studies. In rodent studies it has been found that, if a pregnant animal is subjected to stimuli that maintain a constant state of fear, the offspring are more reactive or emotional later in life.⁷ In addition, emotional females tend to give birth to more emotional offspring. Decreased learning ability of offspring has also been associated with disturbances during the latter term of pregnancy in rats. High levels of stress during pregnancy might also lead to changes in reproductive behavior of offspring when they become adults.⁸ Similar results have been reported for guinea pigs.⁹ It is therefore likely that excessive stress on the canine mother could have deleterious effects on her offspring and so should be avoided, especially during the third trimester of pregnancy. Conversely, providing the mother with a friendly environment that affords positive social contact may facilitate desirable emotional development of her offspring.

There may also be a relationship between fetal position and the behavior of the adult animal. In rats and mice, in utero exposure of females to androgens leads to increased urine marking and mounting, and decreased reproductive success on reaching adulthood, while males located between two females may be less aggressive on reaching adulthood.¹⁰ This effect may be due to the secretion of androgens on adjacent fetuses, or from the androgens transported in the blood flow from a male fetus caudal to the female in the same horn. A similar effect may be seen in dogs, since prenatal exposure of the fetus to testosterone has been shown to prime the central nervous system (organizational effect), so that male behaviors such as leg lifting begin to emerge with maturation, independent of testosterone levels at the time of onset of the behavior.¹⁰

Neonatal stage

During the neonatal period, the puppy spends most of its time nursing or sleeping. Puppies have limited motor ability and, up until about 5 days, movement is on the belly by paddling and stroking with the limbs. By 6–10 days, the forelimbs are capable of supporting weight and by 11–15 days the hind limbs can support weight and walking begins.¹¹ The rooting reflex is present from birth and begins to wane after about 14 days.¹² A slow and sustained pain response to toe pinch is present from birth, but withdrawal and escape from pain do not develop until early in the transition period.¹³ Eyes and ear canals are closed at birth and open by 10–14 days, by which time the palpebral reflex to touch and light and the pupillary responses have already developed.¹² Being unable to hear or see, neonatal puppies are effectively shielded from most psychological effects of the environment. Defecation and urination are reflexes that are elicited by the mother’s licking and cleaning of the perineal region.¹² Temperature regulation is poor at birth and puppies huddle together. They exhibit intense distress and vocalize if they become cold.¹⁴

An important consideration during development is the effect of handling and strong stimuli on the behavioral and physical development of the puppy. One study showed that puppies that have been exposed to short periods of handling from birth to 5 weeks of age were more confident and exploratory than controls.¹³ Handled puppies had increased nervous system maturation, more rapid hair growth and weight gain, earlier opening of the eyes, and enhanced motor development. Thus, early handling may lead to improved learning ability and a more emotionally stable puppy. Similar results were found in a study of kennel-raised and home-raised dogs, with the interesting difference that handled, kennel-raised puppies were better able to handle the stress of isolation.¹⁵ It has been suggested that mild stressors such as early handling affect the pituitary-adrenocortical system in a way that helps the puppy cope better with stress later in life. See also role of mother, Chapter 4.

Transitional period

Toward the end of the second week, the pup enters the transitional stage of its neurological and behavioral development. During this period, the puppy changes from a condition of complete dependence upon its mother to one of increasing independence. The transitional period begins with the opening of the eyes and ears. The auditory evoked startle response usually emerges by 18 days and the puppy may begin to localize sound.¹⁶ The brainstem auditory evoked response also attains the characteristics of the adult at this time.¹⁷ The electroretinogram has the basic features of the adult pattern by 15 days and is fully developed by 28 days.¹⁸ Visual and auditory orientation develops around 25 days.¹³

During the transitional period, the puppy begins to walk rather than crawl, both forward and backward. Puppies begin to exhibit voluntary control of elimination, but the mother still continues to clean their excreta.¹⁹ By the end of the transition period, the puppy begins to interact with other individuals and many of the patterns of adult social behavior appear. Play mouthing by puppies begins to develop and by 4 weeks of age, nipping can be quite painful.¹⁹

Gently exposing the pups to all types of stimuli for short periods each day during this period is likely to enhance physical and mental development. A simple exercise involves allowing pups to crawl or walk on surfaces with differing textures and temperatures. Objects of varying shapes can be moved in front of them in order to promote visual acuity and motor skills. Providing a variety of noise stimuli at low decibels and varied frequencies may facilitate auditory development. Whistles, rattles, music, recordings of environmental noises, and the human voice can be used to provide a variety of auditory stimulation.

Socialization period

The onset and early stages of the socialization period are closely associated with the maturation and myelination of the spinal cord. All sensory systems are functional during this period and learning capacity increases. Although the puppy can support itself and becomes more mobile during the transitional period, normal sitting and standing develop by about 28 days.¹⁹ Teeth erupt and the pups begin taking solid food for the first time. A puppy’s performance in classical and operant conditioning exercises reaches adult levels at about 4–5 weeks, but vision and brainwave function do not reach adult levels until about 8 weeks.¹³ By 4 weeks of age, puppies tend to sleep in groups and at 6 weeks, they start to sleep alone. Weaning begins around 4–6 weeks of age. At first, the puppy begins to show an interest in food, and the mother will begin to decrease nursing contact and may regurgitate food for her young.¹⁹ This is a good time to begin offering appropriate food to puppies. Most puppies are weaned and eating solid foods by about 60 days of age. By 8–9 weeks of age, puppies are attracted by the odors of urine and feces to specific areas for elimination and begin to avoid soiling their den (sleeping quarters).¹⁹

This period is one of rapid development of social behavior patterns.²⁰ At the beginning of this period, the puppy begins to respond to the sight or sound of persons or other animals at a distance. The behavior of puppies during the early socialization period is characterized by a willingness to approach novel objects and, in particular, moving stimuli. Investigative behavior becomes apparent and puppies begin exploring away from the nest area. Social following and early signs of affiliative behavior emerge. During this time, there is a marked increase in interaction with littermates, the mother, and the environment. Distance decreasing and increasing social signaling begin to appear. Gradually, as the mother spends less time with the puppies, the interaction and relationship between littermates strengthen.²⁰

The socialization period is an important time for puppy development. The puppy’s experiences and social familiarity during this period establish the general pattern that will affect almost every social or situational response in later life. By the end of this period, the puppy has formed patterns of response to the situations to which it has been exposed – for well-socialized pups, this should include most things they are likely to encounter later in life.²¹ During the socialization period, the puppy develops attachments to its own and to other species that it encounters socially. It is also a time when the puppy begins to become familiar with and make attachments to places (localization or site attachment), and adapts to many of the stimuli to which it has been exposed (habituation). Because this is the time when social relationships are established, it is essential that puppies have contact with a wide variety of future social partners (people and animals). Neither reward nor punishment needs be involved, although excessive stimuli, whether positive or negative, before 7 weeks of age appear to increase attachments.²²

Besides being a time for the development of social relationships, this also appears to be a period of sensitivity to psychological stress. The sensitivity necessary to facilitate the formation of social relationships also seems to make the puppy vulnerable to psychological trauma. Fear postures begin to emerge at about 8 weeks of age,²⁰ and by 12 weeks sociability begins to decrease and the undersocialized puppy may become increasingly fearful of novel situations and people.¹⁶ Startle reactions to sound and sudden movement become much more pronounced. With time, the puppies learn to discriminate between stimuli associated with dangerous situations and those that are insignificant. Frequent gentle handling has been found to be important for kittens in order to decrease the fear response shown to humans, and the same is probably true for puppies.²³

During the socialization period, social play and exploration become increasingly important.¹³ Play between puppies not only aids in physical development but also provides practice in the development of appropriate adult behaviors, including communication, predation, and sexual relationships. Pups that have the opportunity to interact with other dogs also learn from them by observation. Although solitary play does occur, most play is social, with biting, barking, chasing, pouncing, and mounting being the most frequent components.

It appears that extreme behavior can develop in pups during this period. In a pilot study, puppies were observed during their routine veterinary visit. Each puppy was observed while free in the room, during the physical exam and after the examination, and the preliminary findings suggest there was a set of extreme behaviors displayed by 10% of the puppies in this study. These “extreme” puppies displayed active avoidance, flattened ear position, excessive motor activity, less exploration, lip licking, panting, and extremes of locomotion (increased activity or prolonged inactivity).²⁴

Juvenile period/adulthood

The juvenile period extends from the end of the socialization period to sexual maturity. By 12 weeks, basic learning capacities appear to be fully developed. While object and environmental exploration increase during this period, it is also a time of increasing avoidance, so few, if any, new social contacts are likely to develop. The speed of learning begins to slow by about 4 months, perhaps because previous learning begins to interfere with new learning.¹² By 4–6 months, males begin to show greater attraction to females showing signs of estrus.¹⁹ The final period, adulthood, begins at puberty, which is around 7 months or older in males and 6 months or older in females. Dogs are generally considered to be socially mature at about 18 months of age and fully mature by about 2 years.¹⁹

The wolf as a model to understand the behavior of the dog

Wolves are group-living social hunters who work cooperatively to prey on animals larger than themselves. The understanding of wolf biology and behavior comes from two different sources of information, which often lead to contradictory results: wild packs and captive packs. Classical studies on wolf behavior were done in captive packs where aggression seems to be more frequent and intense than in the wild. More recent research revealed that wolf packs are better described as a family unit consisting of the breeding pair and offspring from successive breeding seasons.²⁷ Experts on wolf behavior currently describe the role of the wolf leaders as parents – guiding, teaching, and caring for their pack members. A parent–family model better describes wolf–wolf relationships than a competitive hierarchy model, which is more typical of captive packs.²⁸ Most social interactions within the pack are affiliative and social conflict is usually resolved through ritualized displays or by dispersion of one or more pack members. Overt aggression is very infrequent between group members in wild wolf packs.

With canine domestication, elements of lupine body language have been lost and there is retention of juvenile characteristics.²⁹ Further complicating matters is the wide diversity in physical and behavioral traits between breeds which may compromise an individual dog’s ability to communicate. In fact, with insufficient socialization with a variety of breeds, some conflicts between dogs may be due to a “failure to communicate” (miscommunication). Studies of both urban and suburban feral dogs have also demonstrated that they do not form packs, nor do they breed cooperatively.^30,31 Studies evaluating this concept have concluded that the theory that canine social groups are organized by a dominance hierarchy “is a human projection that needs replacing.”³²

Canine social groups

Dogs form social groups with rules for interaction based on deference, with individuals giving way to each other based on their history of interaction (previous experience) and individual motivations. For example, a young dog, using aggressive displays, may keep a bone from an older larger dog if the younger dog is sufficiently hungry to risk the fight (resource-holding potential). In fact, dog–dog interactions have been characterized by a combination of resource-holding potential and learning, and not as a result of some form of dominance hierarchy.³³ Genetics, socialization, age, availability of resources, and problem-solving skills (and perhaps which dog was first in the home) might also play a role as to which pet defers in a situation of resource competition. On the other hand, it is not uncommon to find social asymmetries between dogs living together in a household, where one dog is more competent in controlling resources and social interactions. Owners that try to equalize these asymmetries can therefore alter what otherwise might be a healthy social relationship between dogs.

Regardless of the current understanding on wolf social behavior, the many studies showing differences between wolves and dogs, and the lack of any data to support a pack social structure in dogs, the concept of a hierarchical relationship between dogs in a household and dogs and humans continues to be perpetuated.²⁷ Furthermore, training techniques based on dominating the dog through direct confrontation are still favored by some professionals, based on outdated models to explain wolf behavior.

Dogs communicate with each other using body postures, facial expressions, physical interactions, and vocalization as appeasement to avoid confrontations. Therefore, when humans use physical techniques (e.g., pinning, alpha rolls, grabbing the collar) or verbal corrections, this is not the visual, odor, pheromone, and vocal “language” with which dogs communicate. Instead the dog reacts to the person’s actions and emotional state.³⁴ Genetics and temperament, previous experience, the dog’s emotional state, and the level of perceived threat influence how it responds. It should not be surprising therefore that studies have demonstrated that positive training, consistency, and rule structure led to significantly higher levels of obedience, fewer behavior problems, and lower levels of aggression and avoidance behaviors, while punishment led to significantly higher training problems, lower obedience scores, and an increase in avoidance behaviors and aggression toward unfamiliar people and dogs.^35–37 Confrontational techniques, such as hitting, growling, alpha rolls, or even yelling “no,” do nothing to encourage desirable behavior and, in fact, can lead to aggression, especially in dogs that are already aggressive to people.³⁸ Relationships with dogs should not be based on some ill-conceived concept of trying to achieve a dominant status. Instead, they focus on effectively communicating what you want the dog to learn by consistently and predictably rewarding those behaviors that are desirable while ignoring or preventing those that are undesirable. See the avsabonline.org guidelines on dominance for more details.

Vision

Dogs and wolves have a visual system that has been shaped by different evolutionary pressures than those of the human system. Dogs inherited a visual system specialized to hunt at dusk and dawn. They see very well in low levels of light due to the presence of a tapetum behind their retinae which reflects light back to the retinae. They are very sensitive to movement within their visual field. However, dogs are less able to distinguish fine details and have a more limited color perception. Dog vision is dichromatic, so dogs can distinguish some pairs of colors, like blue from yellow, but not others, like green from red.³⁹ These characteristics make the dog better able to hunt small, fast-moving animals that are active in dim light.⁴⁰

Hearing

In terms of the frequency of sound, dogs are able to hear a wider range of sounds compared to humans. The exact range of canine hearing is not clear due to differing results from early studies.⁴¹ However, the best estimate seems to be from 15 000 to 60 000 Hz. They are able to maximize sound capture and localize sounds by moving their pinnae and tilting their heads.⁴²

Olfaction

Dogs have an extremely sensitive sense of smell, which appears to be their primary sense – dogs have been shown to use this over their visual senses when light is adequate as well as when it is poor.⁴³ Dogs have helped, and continue to help, humans in a variety of activities, many of them directly related to their outstanding olfactory perception, from hunting to drug and explosives detection. Over the last few years research has been focused on the potential value of specially trained dogs in the detection of some human diseases, particularly cancer.

Taste

Dogs have taste buds, similar to people, but there are fewer of them, and there are differences in types and distribution. In people, the main types of taste discrimination include sweet, salty, sour, and bitter. Dogs probably do not have a craving for salty foods, based on their taste bud patterns. They can certainly detect bitter tastes, but those taste buds are mainly distributed at the back of the tongue, so a quick lick or gulping could entirely bypass those taste receptors. Dogs also have receptors for meats, fats, and meat-related chemicals, as well as having receptors on the tip of the tongue for water.

Touch

Dogs have sensory nerves across their body surface, just as people do, and touch is as important to dogs as it is to humans. In fact touch may be one of the first senses developed in dogs, and dams start nuzzling and licking puppies soon after birth. Canines have many specialized touch receptors, including vibrissae on the face that can sense air flow. Most dogs enjoy being petted, an endeavor that often brings nearly as much pleasure to their owners.

Auditory communication

Dogs can produce a wide range of vocalizations. Nevertheless, from a practical perspective, there are four that deserve some mention.

Visual communication

Body postures, movements, and facial gestures enable information to be passed quickly between the emitter and the receptor of the signals. Visual communication is useful when dogs are in close proximity but both emitter and receptor must be present. It usually produces a fast response.

When analyzing a dog’s postures and gestures, the most relevant features are considered to be the following: general body posture, and tail and ear position; the gaze and the size of pupils; the lips; movement; and general attitude. All of these must be considered in concert, depending on the context and sequence of their appearance; usually they must be read together since the dog seldom uses an independent signal to communicate. Between group members potential fights are generally resolved by displaying ritual signals and only when there are communication problems do conflicts escalate into aggression.

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