Beware of "scientific studies" regarding link of mammary cancer and skipping heats between breedings

Recently, this discussion came up in our Facebook group: RESPONSIBLE AMERICAN BULLDOGGERS

There was a claim made that there are "scientific studies" regarding a link of mammary cancer and skipping heats between breedings; as in breeding a dog on every heat decreases the risk of mammary cancer.

The following two articles were provided when links to actual studies were requested of the author of the assertion:

Back To Back Breeding of Dams
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By Tanisha Breton on Tuesday, September 10, 2013 at 1:30pm

Recently at an AKC Dog Breeding Symposium held at Michigan State University with key note speaker Dr. Claudia Orlandi Ph.D. (AKC's breeder of the year and author of The ABC's of Dog Breeding) shocked many breeders when it was disclosed that there have been scientific studies to show that it is detrimental for dams to skip heat cycles. It was shared that once you have begun to mate a dam that you should NOT skip any heat cycles until she is completely finished breeding. A dam is said to be "finished" breeding when her litter size is drastically decreased. The study involved following females that were bred every heat cycle and females that were bred every other heat cycle. After they were "finished" breeding, the dams were spayed and their uterus dissected. Those showing most stress, and damage of the uterus were the females that were bred "every other" heat cycle. Part of the rational that skipping heat cycles is harmful stems from the fact that with consecutive heat cycles there is no "flushing action" of the uterus, that normally occurs by having a litter of puppies.The female will go through Estrus no matter if she is bred or not and by breeding a healthy dam back to back,can lesson the chances of the female experiencing pyometra, infections and false pregnancy. The choice to breed or not, should be contingent upon the goals the breeder has and for sure the mental and physical health of the female, above all else. The important information to take away from this study, is that a breeder with healthy females, does have "choices". 2012
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Back to Back Breeding and Pseudopregnancy
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By Debbie Lockhart on Tuesday, February 4, 2014 at 10:43pm

Back to Back Breeding and Pseudopregnancy

The Australian Journal of Professional DogBreeders

February 5, 2011 By Dr Kate Schoeffel

It is frequently claimed that breeding dogs on every heat or “back to back breeding” is bad for a bitch’s long term health and well being. However the research in canine reproduction shows that not breeding a dog when it comes into heat can in fact be bad for its health. Scientist have shown that pseudopregnancy ['phantom pregnancy'] increases the risk of mammary cancers which are the second most common cancer in dogs after skin tumors and are 3-5 times more common than breast cancers in women

1: Pseudopregnancy often occurs when a bitch is not bred. She will show signs such as nesting, weight gain, mammary enlargement and lactation – usually about 6 to 12 weeks after oestrus. Pseudopregnancy represents the extreme of the changes which normally occur during the oestrus cycle and it is suggested that it is a hang over from dogs evolution from wolves. Subordinate nonbreeding pseudopregnant female wolves in a pack can help to raise pups by nursing the litters of other females”

2 In 1994 Donnay and his associates showed that there is a relationship between the number of pseudopregnancies a bitch goes through and the development of mammary cancer


3. Verstegen and Onclin (2006)1 have also studied canine mammary cancer and found that a large number of bitches presented for mammary tumours also show pseudopregnancy, that a large percentage of these females had frequent pseudopregnancies and that the bitches with recurring pseudopregnancy at each cycle tended to develop mammary tumors significantly earlier than other animals. Both of these authors say that there is need formore research but clearly bitches which don’t breed are likely to become pseudopregnant and pseudopregnancy increases the risk of cancer.

Skipping cycles in breeding has been linked to mammary cancer Pregnancy protects against life threatening uterine diseases. The most common uterine disease in the bitch is cystic endometrial hyperplasia. It is linked to several serious uterine diseases including the potentially life threatening disease “pyometra”(literally – a uterus full of pus) which affects nearly one quarter of dogs under 10 years old which are not desexed

4 . According to canine reproduction specialist Dr S. Romagnoli “bitches whelping regularly throughout their reproductive life almost never develop pyometra, while those who whelp rarely or never in their lives have a greater chance of developing this condition”. Furthermore a standard textbook of veterinary internal medicine notes that uterine diseases are less common in kennels where bitches are bred and conceive regularly indicating that pregnancy has a protective effect on the lining of the uterus or “endometrium”

Given that artificially restricting bitches, which haven’t been desexed, from breeding is bad for their health, it is not surprising that many breeding dogs bred have reproductive problems. If they are show dogs they often don’t start breeding until they are three years old, and have finished their show career, and then kennel club rules and even government regulations require that the bitch is only bred on every second season. Frequently older bitches need veterinary intervention to reproduce, and good bitches may end up being bred well beyond 6 years of age when their fertility is beginning to decline.

No responsible breeder who cares about their dogs would breed their bitches until they are exhausted, and rules certainly need to be in place to ensure that irresponsible breeders don’t exploit their dogs, however the current regulations in place in some states do not take into account the biology of the bitch. Breeding should be regulated by limiting the number of litters a bitch can breed or the age at which they should be desexed and retired. Breeding dogs regularly while they are young,followed by desexing and rehoming them early is in the best interest of the bitch and a good pet breeder can use this knowledge to work with the natural biology of their animals. Breeders must be aware of and comply with any government regulations regarding dog breeding in their state and unfortunately in Victoria, NSW and QLD current regulations do not permit this approach to dog breeding.
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First, these are not studies but summaries with no methodology or the actual study results. Details are missing. For example, was genetic cancer controlled for in the study? When you go to the doctor, you are asked if you have history of cancer in your family for a reason. What was the difference of probability of acquisition of cancer between the groups?
Second, does this apply to American Bulldogs? What breed was the study based on and what were the medical histories of the dogs in both groups? Which dogs had a history of mammary cancer in their ancestry?
Third, these findings do not jibe with @Olga 's personal experience of breeding ABs for 16 years, and not a single female that was bred with the method of skipping heats between breedings got mammary cancer.
NOT ONE OUT OF DOZENS OF DOGS.

Mammary cancers are usually caused by hormonal disbalance, which is largely GENETIC.

These summaries are worthless without actual methodology and results.