Topical Insecticides and Reproductive Health in Dogs

Be cautious about using topical insecticides on breeding dogs, lest they get “Homer Simpson Sperm” syndrome!

I spent Sunday at a very interesting Canine Reproduction seminar. The session, which lasted roughly two hours, was presented by MiniTube Canada, and was a bargain at $15. Unlike a lot of corporate seminars, this one was not geared solely towards selling you equipment, although there was discussion about the equipment the company makes (primarily semen extenders and shipping containers). Our presenter was Dr. John P. Verstegen DVM, MSc, PhD , DECAR, Minitube’s director of small animal reproduction. Since I’ve recently had my first transcervial insemination done on a bitch (Delilah), it was impressive to hear Dr. Verstegen say that he estimates he has performed more than 19,000 of them over the course of his career.

Dr. Verstegen had a lot of interesting information to share, but something interesting jumped out at me during the portion of the seminar devoted to the topic of managing sperm count in the male dog. Dr. Verstegen mentioned a study he had taken part in examining the effects of topical insecticides (ie; flea and tick treatments) on the reproductive health of the male dog.

During the study, 3 groups of dogs were given –

1) the normal recommended dosage of topical insecticide

1) 3 times the normal recommended dosage of topical insecticide

1) 5 times  the normal recommended dosage of topical insecticide

Even when given the normal dosage, 4 out of ten dogs developed some form of sperm abnormality. At five times the recommended dose, almost the entire control group developed sperm abnormalities. This is quite shocking, especially when one consider the wide variance of weight recommendations on the packaging for most topical insecticides. Revolution for “small dogs”, for example, has a weight variance of 11 – 22 pounds, meaning that a dog double in size is receiving the same dose as a dog half as large. Dr. Verstegen mentioned that similar effects had been seen on oocytes (egg cells).

For our male dogs, it takes 75 days for a sperm to be produced and become viable. This means that simply stopping application of topical insecticides on breeding males when the female is due to come into heat will not help to offset the effects of the insecticide on sperm production, because the sperm which will be used to inseminate the bitch will have been produced during the period when the insecticide was still being applied.

Instead, it seems apparent to me that we must consider using an alternative approach to flea and tick management in our breeding dogs, if we want to maximize the chances of successful conception.

Dr. Verstegen told me that the study he mentioned, and which I refer to above, has been published, so I’ll link to it as soon as I hear back from him.

In the meantime, I did find this information on imidacloprid, an insecticide found in Bayer’s Advantage family of topical flea medication –

Neonicotinoids (imidacloprid, dinotefuran), a relatively new class of pesticides, are also associated with organ damage, and neurotoxic effects. Dinotefuran, a broad spectrum insecticide, causes decreased motor activity seen after acute dosing and increased motor activity after repeated dosing.8 It may also be responsible for endocrine-related toxicity manifested in the reproductive toxicity studies (in rats) as decreases in primordial follicles and altered cyclicity in females, abnormal sperm parameters in males. Changes in testes and ovary weight were also seen in several species, including dogs.9 Similarly, imidacloprid is linked to reproductive and mutagenic effects, – it has been determined that imidacloprid increased the frequency of genetic damage by chemically binding to DNA – as well as neurotoxic effects as manifested by tremors, uncoordinated gait and decreased activity.

Be VERY CAREFUL about using so-called “alternative” remedies for treating fleas! One common recommendation you’ll find on the internet and on home remedy mailing lists is a suggestion to use “Sevin”, a commercially sold powdered form of garden insecticide.

Sevin has a well documented history of being associated with reproductive hazards in pets (and in people).

From CAP –

A 1980 U.S. Environmental Protection Agency (EPA) review cited four studies (three in rats, one in another rodent) showing decreases in sperm numbers, an increase in sperm abnormalities, and a decrease in sperm mobility caused by carbaryl exposure.38 A 1986 review cited three other studies of rats with similar results.29 Some of these studies found effects at low doses. For example, 7 mg/kg per day (about 1/35 of the LD50) given over a period of nine months reduced sperm mobility and the numbers of sperm-forming cells.39

Females: Female laboratory animals of a number of species fed carbaryl suffer from reproductive problems. A 1986 review summarized 25 studies that had found reproductive problems caused by carbaryl in eight different kinds of animals. These problems included reduced fertility, increased fetal mortality, low birth weights, reduced growth and survival of babies, and birth defects.29 Some effects occur at surprisingly low doses. For example, rats fed carbaryl in doses equivalent to 1/35 of the LD50 for one year had estrous cycles significantly longer than unexposed control rats39 and pregnant monkeys given daily doses as low as 1/100 of the acute lethal dose had increased rates of spontaneous abortions.40

Not only would I not use it on pets or breeding dogs, I would not even use it in my garden.