According to a new study, dogs born between June and August are more likely to suffer from heart disease, with dogs born in July specifically at risk.
The study, which was carried out by researchers at the Perelman School of Medicine at the University of Pennsylvania, believe they have identified why - pollution.
To reach their conclusions, scientists studied data from the Orthopaedic Foundation of Animals on 129,778 canines made up of 253 different breeds - some which are known to be predisposed to heart disease and some which aren't.
On the importance of learning more about heart disease in dogs, Mary Regina Boland, PhD, an assistant professor of Informatics in Biostatistics, Epidemiology, and Informatics says, "It's important to study dogs because the canine heart is a remarkably similar model to the human cardiovascular system.
"Also, humans and dogs share their lives together and are exposed to similar environmental effects, so seeing this birth season-cardiovascular disease relationship in both species illuminates mechanisms behind this birth-season disease relationship."
Dog breed v birthday: Which poses the greater threat?
Since some dog breeds are known to be more likely to develop heart disease than others, when studying dogs who are genetically predisposed to heart disease, scientists found that the dog's birth date had a marginal impact on the dog developing the disease - perhaps because they were already predisposed to the disease - leading researchers to suggest that heart disease acquired later in life may have broader links to the dog's birth month, among all breeds.
When studying dog breeds not genetically predisposed to cardiovascular disease - the Norfolk Terrier, Berger Picard, American Staffordshire Terrier, English Toy Spaniel, Bouvier des Flandres, Border Terrier and Havanese - were found to be most at risk, with Norfolk Terrier and Berger Picards puppies at a greater disadvantage of developing heart disease when born in July.
Overall, scientists working on the study found that dogs have a 0.3-2% risk of developing heart disease, depending on breed, and have revealed that the risks are at their greatest for dogs born in July, where dogs born during this month have a 74% greater risk of developing the disease.
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So, why does Summer pose a threat to a dog's heart health?
Researchers working on the study believe the answer to why dogs born between June-August are at a greater risk of developing cardiovascular disease lives in the environment as it is a peak period for exposure to 'fine air particles, such as those produced by factory pollen'.
On the connection between dogs and humans, researchers say, "Outside air pollution during pregnancy and at the time of birth appears to play a role in later development of heart disease."
In a previous study, the team alaysed data from 10.5 million human patients around the world and noted that there was a definite link between first-trimester exposure to fine air particulates and nine percent increased risk of the heart rhythm irregularity known as atrial fibrillation (Afib) later in life.
Afib afflicts two percent of people under 65 in the United States (5.5 million people) with those exposed to peak air pollution during the first trimester of their mother's pregnancy found to be at a 9% higher risk.
When reviewing both the canine and human studies side by side, the canine study's authors believe that the link to heart disease and birth months should be investigated further, adding, "Because dogs' pregnancies are shorter then humans, the proposed mechanism is still thought to be through the mother's inhalation of air pollution effecting the uterine environment, which in turn effects the developing cardiovascular system of the baby or puppy."
The team believe that future studies may reveal more about other diseases linked to birth months as well as why specific breeds are more susceptible to cardiovascular disease.