One of the best traits a bitch can have in the eyes of a breeder is good mothering ability. Unfortunately, it is not a trait often considered when choosing a bitch to breed; or the female relatives (especially mothers and daughters) of the stud dog to be used. Mothering ability has a strong hereditary aspect, but other factors exert influence as well.
There are four hormones that trigger aspects of mothering behavior: estrogen, progesterone, prolactin and oxytocin. Estrogen is the most active hormone in reproduction from its primary actions in stimulating the physical and behavioral changes associated with estrus (swollen vulva, bloody vulvar discharge and pheromones to attract male dogs), to its secondary role as it also acts as a priming hormone for the other three in preparation for mammary development, lactation and maternal behavior. In order for the estrogen molecule to trigger a response, the target tissue must have estrogen receptors on the cell membranes. The location of the receptors within the brain, and the concentration of the receptors, will determine the type and strength of the response. Progesterone is recognized as the pregnancy hormone. The ovarian follicular cells start to change after ovulation and secrete progesterone to maintain pregnancy. It has some effect on inducing maternal behavior, particularly when its receptors are primed with estrogen. Just before birthing progesterone levels drop abruptly, with a concurrent rise in prolactin. The combination seems to be largely responsible for stimulating immediate mothering behavior such as nesting, and protective maternal aggression. Prolactin's function is largely stimulatory for lactation. Both actions of prolactin, maternal behavior and lactation, are enhanced if estrogen has "primed" the tissues. Lastly, oxytocin is released from the pituitary gland in response to the physical pressure of a puppy against the cervix during labor. One of the actions of oxytocin is to synchronize contractions of the uterus in birthing, and to stimulate the let-down of milk. In conjunction with the other hormones, it stimulates maternal recognition of her pups and care behavior.
Other than the behavior exhibited in the estrous cycle and breeding, there are not behaviors specifically associated with pregnancy until the dam nears labor and delivery. At that time she will exhibit nesting behavior, typically searching out a protected, private place where she can feel safe.
Once the puppies are born, if appropriate hormonal activity has occurred, the dam will begin her mothering by licking them. Initially it is the scent of her amnionic fluid that communicates that the puppies are her's. The dam performs the licking in order to stimulate breathing, and dry the pups' coats. Later she will lick the genitalia of each pup to stimulate urination and defecation since the pups won't eliminate on their own until about 3 weeks of age. The bitch will also use licking on the heads of the pups to guide them nurse.
Some behaviors post-partum are undesirable. Dams may be aggressive to their pups, especially when the pups are making noise. Causes of this aggression can be varied. The first consideration is if the bitch is in pain. Mastitis is a condition that can cause pain, which can trigger aggressive behavior towards the pups. Sometimes the problem is that the bitch does not recognize the pups as her own. Inadequate levels of oxytocin can influence this, as the hormone makes the brain receptive to the amniotic fluid smell immediately after birth and pheromone secretion. Another factor is if the pups are removed as soon as they are born and cleaned up so thoroughly that when returned to the bitch they don't have the amnionic fluid scent to identify them as hers.
Aggression can escalate to cannibalism of one or more of the pups. This type of cannibalism is called kronism. Again, pain can be the cause, and as before, mastitis needs to be considered. Pre-eclampsia, a condition where the bitch's blood calcium (unbound) is too low, but she isn't yet exhibiting the classic signs of seizures, fevers and weakness - can be triggering the aggression. Other causes can be hereditary (lack of estrogen receptors which would negatively impact the action of other hormones), psychological (first time mom, very nervous, etc), and physiological (too much noise, too much foot traffic in the nursery, over-crowding in the nursery area, etc) that results in continued neurotransmitter release.
On a less aggressive level, rejection of the pups can be a problem. If it is just one or two pups, it may indicate something is wrong with those particular pups, whereas if it is the entire litter, the problem usually lies with the dam. It can be more common in first litter bitches. Usually if it involves just one or two pups, they may be cold, or too still. The three big threats to the survival of neonates is hypothermia, hypoglycemia and dehydration. If caught soon enough, the pup can be slowly warmed, or if dehydrated, bottle fed to stimulate activity. Do not attempt to feed a cold puppy. They are not capable of swallowing and may aspirate the milk into their lungs instead. Once the puppy has reestablished a normal body temperature, the dam will accept it. It is important to note that occasionally rejection will escalate to cannibalism.
In summary, lack of appropriate maternal behavior can be a result of hormonal imbalance, pre-labor caesarian surgery (lack of pressure on cervix during labor), genetic propensity for inadequate hormone receptors, lack of experience, elevated neurotransmitter release due to stress, or in reaction to pain.