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 == Early Spaying in Dogs == 
 On another note, does anyone have any good scientific studies supporting spaying female dogs prior to the first estrus cycle to prevent the mammary gland from being stimulating by hormones and therefore also prevent breast cancer. I have heard vets and read many things over the internet, but never have seen any definitive study. Can anyone help. 

     I think whether ""bitch"" has been losing favor depends a great deal on one's experiences. As I mentioned below, the vast majority of people I know use the term freely; others obviously have different experiences. 

     At any rate, I actually wanted to address your question about ovariohysterectomy (spay) preventing mammary tumors. The study everyone references was done in 1969 - here is the citation: 

         Schneider, R, Dorn, CR, Taylor, DON. Factors Influencing Canine Mammary Cancer Development and Postsurgical Survival. J Natl Cancer Institute, Vol 43, No 6, Dec. 1969 

     That study showed that the fewer estrus cycles a bitch had before she was sterilized, the lower her risk of mammary tumors. There are a couple of papers which review the medical literature on sterilization and long-term health effects (both are .pdf files): 

         http://www.naiaonline.org/pdfs/LongTermHealthEffectsOfSpayNeuterInDogs.pdf 
         http://avmajournals.avma.org/doi/pdfplus/10.2460/javma.231.11.1665 

     Hope that helps! Newcastle (talk) "