I submitted my original question on this subject to IRS via email shortly after posting it here. I didn't anticipate a timely IRS response. To my surprise, an IRS email arrived today! Here is the "official" IRS answer (or at least the official response of one IRS employee):
The Answer To Your Question Is:
Thank you for your inquiry of March 19, 2008. I understand you have a question concerning the depreciation of a working dog.
A working dog is an asset of the business. Dogs are not listed separately in the publications because many people would try to depreciate or deduct the costs of the family pet. A family pet is not deductible.
You will be able to depreciate the cost of obtaining a working dog. The recovery period of an asset used in animal husbandry is 7 years under the general depreciation system and 10 years under the alternate depreciation system.
You will also be able to deduct the ordinary and necessary expenses of keeping a working dog. These costs include the cost of food and veterinary care.
References
- Publication 946, How to Depreciate Property