A Comparison of Aggression During Pre-Pregnancy and Three Gestation Periods in Canines

Aggression is caused by a variety of different stimuli, which yields a hostile response in animals. This type of behavior is well-studied in canines, especially since humans often take on dogs as companions. This experiment proposal suggests conducting research on twelve different dog breeds. Initial tests would include submitting the dogs to both a female and male intruder on separate occasions. Then the dogs would be artificially inseminated and be submitted to both tests again during three periods of their gestation (early- 20 days, mid- 40 days, and late- 60 days). The purpose of the study would be to test aggression before and during gestation and compare amounts of aggression throughout all four periods. Additionally, the study would look at aggression towards a male and female intruder to see if aggression is higher towards like-sexed or opposite-sexed individuals. This study could offer insight into aggressive behavior of dogs, thus giving valuable information to breeders, veterinarians, animal control officers, and others people who work with canines on a daily basis.

Introduction:

Aggression is a hostile behavior that is elicited by a stimulus, with different types of stimuli leading to different types of aggression (Knutson 1973). Aggression is especially common and well studied in domestic dogs (Canis familiaris). Aggression can often be observed by dogs biting or growling (Farago et al. 2010; Maragliano et al. 2007). Numerous factors influence canine aggression, including environmental factors; a game of tug-o-war, food guarding, and other approaching dogs can elicit an aggressive response (Farago et al. 2010). There are also biological factors that affect aggressive behaviors; smaller dogs, older dogs, male dogs, and dogs that are not spayed or neutered tend to be more aggressive (Hsu et al. 2010). Another example of a biological factor is the increasing and decreasing of hormones during gestation.

Aggression in pregnant animals has been studied before in golden hamsters (Giordano et al. 1986; Wise 1974), rats (Rosenblatt et al. 1982; Erskine et al. 1978), and mice (Buhot-Averseng 1983). Aggression in pregnant female dogs is common, but it is not as well studied and information regarding hormone-induced aggression is mainly reported from dog owners and veterinarians who have had experience with gestating dogs (Clemons 2010). In golden hamsters, rats, and mice there are correlations between the pregnancy stage (early, mid, late) and aggressive behavior towards female intruders (intrasexual aggression). Graphs from the studies (Giordano et al. 1986 [figure 1]; Wise et al. 1982 [figure 2]; Rosenblatt et al. 1994 [figure 2]) show an increase in aggression (attacks and chases) through early pregnancy, with aggressive behavior peaking at mid-pregnancy and then decreasing after.

Aggression throughout pregnancy is correlated with hormonal changes. Giordano et al. (1986) explains that aggressive behavior peaks the same time (mid-pregnancy-11 days) as estrogen levels do. When aggressive behavior is at the lowest point (day 15) for the gestation period, estrogen begins to decline. In this same study, progesterone levels remain constant throughout early and mid-pregnancy. Progesterone rises sharply just before aggressive behavior reaches its lowest point and then decreases.

Aside from hormonal changes, Wise et al. (1982) citing Marler (1976) suggests that aggression during pregnancy reflects competition of resources (such as food, water, and space) and competition should be greater for like-sexed individuals than opposite-sexed individuals. In the studies involving rats, mice, and golden hamsters there was more aggression towards female intruders than male intruders.

For my potential experiment, I wish to study aggressive behavior in female dogs during the different periods of pregnancy, including early (20 days), mid (40 days), and late-pregnancy (60 days). I would also like to test aggressiveness towards male intruders and female intruders throughout the gestation periods. In order to evaluate aggression, the female dogs will be subjected to two tests: an encounter of a female intruder and of a male intruder (as modeled in the mouse, rat, and golden hamster experiments). All female dogs will be tested before their pregnancy in addition to each of three gestation periods. Aggression will be measured by the time span of a growl and number of times the dog attempted to bite at the female intruder and the male intruder within a one-minute test period. Based on the previous research done on rats, mice, and golden hamsters, including hormonal changes and the difference in aggressive behavior towards male and female intruders, I predict that the gestating dogs will be more aggressive during the mid-pregnancy period than any of the other three stages (post, early, mid, and late). I also predict that the dogs will display more aggressive behavior towards the female intruder than the male intruder in all three stages of pregnancy.

Methods:

Dog Selection

For my study I will choose female, non-spayed purebred dogs. According to Hsu et al. (2010), temperament in dogs is often based on size. The study cites Chihuahuas and Shih Tzus as being the most aggressive towards other dogs and Golden Retrievers as being the least aggressive. I will use the same breed dogs as this previous experiment (minus the other breeds and mixed breeds) in order to get a pool of different dogs with different known temperaments. The dog breeds will include Golden Retriever, Labrador Retriever, Siberian Husky, Toy Poodle, Chihuahua, Miniature Schnauzer, Dachshund, Beagle, Maltese, Yorkshire Terrier, Pomeranian, and Shih Tzu. In order to replicate the experiment, we will choose three female dogs from each breed. Dogs will be from local breeders and will be full grown and aged between 2-3 years, which is an ideal age for breeding canines.

Pre-pregnancy trials

All 36 female dogs will be submitted to the first aggression test prior to breeding. The test will take place in an 18x20 enclosed room with a window through which the observers can record the dogs' behavior. Inside the room will only be the certified dog trainer who will handle each individual dog during the test. The test dog will be allowed to sit in the room for three minutes in order to acclimate to the settings. After three minutes, another trainer will enter the room with another female dog (a mixed breed dog that is also 2-3 years of age). The intruding female dog will be allowed to approach the test dog until it is three feet away (to prevent either dog from actually being bit). The two dogs will be in each other's presence for a minute. A day after the test with the intruding female dog, the experiment will be repeated using an intruding male dog instead. During both tests data will be collected (see Data Collection and Comparison below).

Breeding and Care

Each female dog will be artificially inseminated while in heat, which will most likely range from a few days to a few weeks after the initial test. The breeding will take place under the care of certified dog breeders in a laboratory setting. During the periods from the initial test to breeding to the parturition day, each individual dog will be kept and taken care of in a laboratory setting in order to keep the dogs under similar control conditions. They will be allowed two hours of exercise outside in an enclosed yard everyday with a certified dog trainer and will also be fed dry dog food twice a day and have constant access to fresh water. The dogs won't be allowed any interaction with one another, as to prevent any aggressive behavior between each other that might alter results. Pregnancy will be confirmed and tracked using ultrasonography as described in Luvoni et al. (2006). A crew of three certified veterinarian technicians and one veterinarian will oversee the group of 38 dogs (the 36 gestating female dogs and the one intruding female dog and the other intruding male dog). Dogs that are not impregnated during the insemination process will be excluded from the experiment.

Pregnancy Trials

After each dog starts the normally 65-day gestation period, the two tests will once again be performed during each period of the pregnancy, including early-pregnancy (20 days), mid-pregnancy (40 days), and late-pregnancy (60 days). The exact same two tests will be conducted as described in the Pre-pregnancy Trial section.
Data Collection and Comparison

Data collected during the trial will include the number of bites and the collective growl time for the one-minute test period per each of the 36 impregnated dogs. In this specific study, the amount of bites and the total growl time will be compared to the amount of bites and total growl time for all four tests (pre-pregnancy, early pregnancy [20 days], mid-pregnancy [40 days], and late pregnancy [60 days]) for each of the two intruding dog tests.

Results and Discussion:

There are numerous potential outcomes to our proposed experiment. My original prediction is that there would be more signs of aggressive behavior (longer collective growl time and higher bite occurrence) during the mid-pregnancy period. Results that would support my prediction include data that shows more biting occurrences and longer growl length time during the mid-pregnancy test than any of the gestation period tests. This would also agree with previous research on hormonal changes and aggression in pregnant mice, golden hamsters, and rats, which showed an increase in aggression during mid-pregnancy. It could suggest that there are similar hormonal changes that occur in canines as well. Also, results that show more aggression towards the intruding female dog than the intruding male dog would also support my prediction and the theory that intrasexual aggression can occur during gestation due to the competition of resources (Wise et al. 1982 cites Marler 1976).

However, other outcomes are always possible. I could find that any of the tests at the different pregnancy periods showed higher bite occurrences and longer growl length times than the other tests. This could indicate that hormonal changes are different among canines and that there are different increases and decreases in hormones during the gestation period. I could also find that the growl length times and bite occurrences are the same among each dog for every single test. This could simply indicate that certain dogs are just more or less aggressive in general than others. Similarly, dogs can be equally as aggressive towards both intruders or more aggressive towards the male intruder. This could indicate that some dogs are just aggressive towards any intruder or that something about the male intruder creates a bigger stimulus for aggressive behavior.

Studying aggressive behavior in dogs can be extremely helpful to veterinarians, breeders, animal control officers, and other people who work with dogs on a daily basis. Understanding temperament of dogs can also help reduce aggressive behavior from dogs towards humans as well. I believe my potential study could help people who work with dogs on a daily basis better understand temperament of dogs, especially dogs that are impregnated.

References

Buhot-Averseng, M. 1983. A Graphic Representation of the Effects of Cohabitation Upon Aggression in Pregnant Mice. Aggressive Behavior. 9, 253-258.

Clemons, G. L. 2010. Canine aggression: The development and correction of canine aggression. Canis Major Publications.

Erskine, M. S., Barfield, R. J., & Goldman, B. D. 1978. Intraspecific fighting during late pregnancy and lactation in rats and effects of litter removal. Behavioral & Neural Biology. 23, 206-218.

Farago, T., Pongracz, P., Range, F., Viranyi, Z., & Miklosi, A. 2010. 'The bone is mine': affective and referential aspects of dog growls. Animal Behaviour. 79, 917-925.

Giordano, A. L., Siegel, H. I., & Rosenblatt, J. S. 1986. Intrasexual Aggression During Pregnancy and the Estrous Cycle in Golden Hamsters (Mesocricetus auratus). Aggressive Behavior. 12, 213-222.

Hsu, Y. & Sun, L. 2010. Factors associated with aggressive responses in pet dogs. Applied Animal Behaviour Science. 123, 108-123.

Knutson, J. F. 1973. The Control of Aggression. Aldine Publishing. Chicago, IL. 12-13.

Luvoni, G. C., Beccaglia, M. 2006. The Prediction of Parturition Date in Canine Pregnancy. Reproduction in Domestic Animals. 41, 27-32.

Maragliano, L., Ciccone, G., Fantini, C., Petrangeli, C., Saporito, G., Di Traglia, M., & Natoli, E. 2007. Biting dogs in Rome (Italy). International Journal of Pest Management. 53, 329-334.

Rosenblatt, J. S., Factor, E. M., & Mayer, A. D. 1994. Relationship Between Maternal Aggression and Maternal Care in the Rat. Aggressive Behavior. 20, 243-255.

Shimatsu, Y., Yuzawa, H., Aruga, K., & Nakura, M. 2007. Effect of Time for Mating and Gestation Length on Reproductive Efficiency in Dogs. Reproduction of Domestic Animals. 42, 664-665.

Wise, D. A. 1974. Aggression in the female golden hamster: Effects of reproductive state and social isolation. Hormones and Behavior. 5, 235-250.

Wise, D. A., Ferrante, F. 1982. Effect of Conspecific Sex on Aggression During Pregnancy and Lactation in Golden Hamsters. Aggressive Behavior. 8, 243-251.