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When do puppies develop their sense of smell? Interestingly, puppies are capable of using their sense of smell even before they are born! 

What's even more interesting though is that there seems to be an evolutionary advantage as to why a pup's sense of smell is present so soon.

 And this isn't exclusive to puppies, it's something that apparently occurs in human infants too! Read on to learn more.

aniseed study puppies

The Aniseed Study

In a study conducted by Peter G. Hepper and Deborah L. Wells and published on Oxford Journal, 16 pregnant dogs were divided into four groups composed by four dogs.

The first four pregnant dogs were fed a diet flavored with aniseed, a spice known for its aromatic scent and for being safe to use in dogs. The pregnant dogs were fed this diet during the last 20 days of gestation. 

The second group of four dogs were fed the aniseed flavored food the day after giving birth for the duration of 20 days. The puppies were expected to be indirectly exposed to the aniseed scent/flavor when suckling for the first 3-4 weeks. 

The third group of pregnant dogs were fed the aniseed flavored food both before the birth of their puppies and afterward. Finally, the fourth group of pregnant dogs were fed a normal diet with no aniseed flavor added.

The Intriguing Results


During the study, the puppies stayed in their owner's home and none of them were exposed to aniseed other than indirectly from the mother's diet.

All puppies were weaned from milk to solid food at around 4 to 5 weeks of age, and at 10 weeks, when the puppies were tested, all of them were eating solid food.

In the test, the puppies were tested by offering them a choice between some minced chicken with a drop of aniseed and some minced chicken with distilled water. These foods were offered over the course of several days.

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The strongest preference for the aniseed flavored chicken was observed in the puppies who were exposed to aniseed both prenatally (in the womb through amniotic fluids) and postnatally (from the mother's milk).

Little interest for the aniseed flavored chicken was shown in both the puppies exposed to aniseed exclusively when in the womb or exclusively when nursing.

Practicing Breathing Muscles

Further proof of puppies using their sense of smell when still in the womb comes from taking a peek at them via ultrasound. Through an ultrasound, scientists were capable of gaining an "inner view" of what goes on in the womb two weeks prior to the puppies being born.

The scientists found that the puppies were "exercising" their breathing muscles during this time. 

It's likely that this "breathing time" provides puppies the opportunity to learn more about their mother's distinct odor and the odor of the food she has been eating, suggests animal behaviorist John Bradshaw in the book "Dog Sense: How the New Science of Dog Behavior Can Make You A Better Friend."

An Evolutionary Role

Why would puppies rely on their sense of smell when they are still in the womb? Interestingly, there may be an evolutionary advantage.

This form of chemosensory prenatal learning may aid the puppy in learning what foods are safe to eat when weaning time is around the corner.

With smells passing through the amniotic fluid, and then flavors passing in the milk, puppies may rely on their mother's knowledge to learn about which foods are safe to eat and this can influence the puppy's future dietary preferences.

These two types of prenatal and postnatal exposure, provide the puppies with a longer period of experience on what's safe to eat, important factors that aid in promoting their survival, further explain Peter G. Hepper and Deborah L. Wells in the study. Quite fascinating, huh?


  • Perinatal Olfactory Learning in the Domestic Dog, Peter G. Hepper, Deborah L. Wells, Oxford Journal, Chem. Senses (March 2006) 31(3): 207-212.
  • Mennella, J.A., Johnson, A. and Beauchamp, G.K. (1995) Garlic ingestion by pregnant women alters the odor of amniotic fluid.Chem. Senses, 20, 207–209.

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