As of this moment, this is a hot topic, and solid answers are hard to come by. There have been new studies, and revisiting of old studies.. Unfortunately, this makes it difficult to give exact guidelines.
Currently (as of September, 2018, these are our recommendations:
Cats: 5-6 months.
Dogs: General recommendations listed first, followed by breed specific recommendations Spay- Female (ovariohysterectomy)- 7-12 months of age Neuter- Male- 16-18 months
Golden Retrievers, Labrador Retrievers, Rottweilers: Females- 10-12 months Males- 16 months
Vizlas: Males and Females- 10-12 months
Female dogs tend to have their first heat cycle anywhere from 7-13 months of age. The “heat cycle” of the female dog lasts 21 days. There is usually about 10 days of blood tinged vaginal discharge. This is the only time the female dog is receptive to the male, and open to reproduction.
The above recommendations are based off our doctors current best assessment of the literature available.