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Local study published on developmental malformations in deer

 

By Michael Howell

According to local wildlife rehabilitator Judy Hoy, the elk and deer and other ruminants in the Bitterroot Valley have something more to worry about than wolves, and that is endocrine disrupting chemicals in the environment.

A study, conducted over a 14-year period between 1996 and 2010, and authored by Hoy, her husband Bob, local biologist and taxidermist Gary Haas of Big Sky Beetle Works, and Dr. Pamela Hallock, a researcher and professor at the University of South Florida, was recently published in the journal Wildlife Biology in Practice.

In the study, entitled “Observations of Brachygnathia Superior in Wild Ruminants in Western Montana, USA,” over 1000 white-tailed deer, and small samples of other hunter-killed grazing animals, including elk, mule deer, pronghorn antelope, bighorn sheep and two domestic species, calves and goats, were examined for facial bone and tooth malformations. This long-term study was done with no funding, as a public service.

The study was done because of observations of brachygnathia superior, the underdevelopment of the premaxillary bone and other facial bones, resulting in underbite on elk calves, mule deer fawns and white-tailed deer fawns cared for at the Bitterroot Wildlife Rehabilitation Center (BWRC). According to numerous studies, brachygnathia superior is a definitive symptom of fetal hypothyroidism during the development of a fetus. Other bone malformations and underdeveloped organs as a result of fetal hypothyroidism have not been observed to be as common as brachygnathia superior/underbite. The first observations of bone malformations, including brachygnathia superior, in wild and domestic animals was in spring of 1995. The study data indicate this condition appeared abruptly in multiple species and has greatly exceeded any previously documented prevalence of cranio-maxillary malformations in wild ruminants. Photos on the web, in hunting magazines and samples of ruminants examined from other states indicate brachygnathia superior is now widespread in wild and domestic populations throughout North America, including Alaska and Canada.

A study done by the eminent wildlife biologist, Dr. Bart O’Gara, in winter of 1991-92 on 100 white-tailed deer and 32 fetuses collected on the Lee Metcalf Wildlife Refuge north of Stevensville, documented no malformations of any kind. No malformations were observed on mammals at BWRC prior to 1995. An extensive study of bone and facial malformations on over 36,000 white-tailed deer done by L.A. Ryel in Michigan in 1969, found no deer with brachygnathia superior or underbite. These studies show brachygnathia superior was not a normal variation in wild ruminants or at all common prior to 1995.

Since 1995, brachygnathia superior has been observed and documented with photos on multiple species of bird in Western Montana by Hoy at the Bitterroot Wildlife Rehabilitation Center, other rehabbers and many bird photographers. This bone malformation has become fairly common on puppies and kittens and has been observed on wolf pups. It is also reported to be a problem throughout the world on human newborns.

In spring of 1996, to determine prevalence of underbite, Hoy began measuring the anterior facial bones on accident-killed ruminants collected by Bob Hoy as game warden for Northern Ravalli County and on hunter-killed heads provided by hunters.

The Hoys teamed up with independent biologist Gary Haas of Florence, who began observing a noticeable increase in bone and tooth malformations on multiple species of hunter-killed game animals in 1998. Dr. Hallock joined the team because of observations of malformed shells on forams, a one celled ocean animal, in the same time period as the high prevalence of facial and limb bone malformations on ruminant species in 2001.

The percentage of underbite on the team’s main study animal, white-tailed deer, increased each year until it peaked in 2001 at 56%. The rate of underbite then went down each year through 2006 to 33%.

Alarmingly, the underbite prevalence in white-tailed deer fawns born spring of 2007 spiked to over 70%, more than double the 2006 rate and has averaged around 70% each year since. Underbite makes it difficult for a grazing animal to procure enough nutrition, the primary reason many of the females are unable to produce viable young and young animals fail to grow properly and gain weight after weaning.

The authors attribute the widespread deformations to endocrine disrupting chemicals in the environment that are associated with fetal thyroid dysfunction that results in such deformations.

“The prevalence of brachygnathia superior on ruminant species we are reporting,” states the report, “is far higher than has previously been reported (to our knowledge) for a bone malformation in a wild mammal population and likely greater than previously found in any ruminant species. The study concludes that underbite and the other serious symptoms of fetal hypothyroidism are likely a significant factor in the decline of wild ruminant populations in Montana and other western states.

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