You might discuss Ovariectomy rather than Ovariohysterectomy with your vet as OE has several advantages:
Making a Rational Choice Between Ovariectomy and Ovariohysterectomy in the Dog: A Discussion of the Benefits of Either Technique
BART VAN GOETHEM, DVM 1 , AUKE SCHAEFERS-OKKENS, DVM, PhD, Diplomate ECAR 1 , and JOLLE KIRPENSTEIJN, DVM, PhD, Diplomate ACVS & ECVS 1
1 From the Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
Conclusions—OVH is technically more complicated, time consuming, and is probably associated with greater morbidity (larger incision, more intraoperative trauma, increased discomfort) compared with OVE. No significant differences between techniques were observed for incidence of long-term urogenital problems, including endometritis/pyometra and urinary incontinence, making OVE the preferred method of gonadectomy in the healthy bitch.
The American version
A Spaying Dilemma: Laparoscopic Ovariectomy as an Alternative to a Traditional Ovariohysterectomy
A fun little on-topic blog
Unfortunately both OE & OVH affect bone growth/density with bone loss ocurring as estrogen levels disappear; a calcium deficient diet should be avoided.
One of the overriding concerns given for determining "when to spay" is the oft quoted risk of mammary neoplasms:
A beautifully presented article appears in the Irish Veterinary Journal (January 2009) Mammary tumours in dogs
The earliest study to recognise an increased risk of mammary neoplasia associated with remaining sexually entire was performed by Schneider et al. in 1969. This study yielded data that indicated that the relative risk of mammary neoplasia development was as low as 0.5% for bitches undergoing ovariohysterectomy before their first oestrus when compared to bitches that remained entire. While the original data from 1969 have not been superseded, it must be stated that the conclusions drawn are based upon remarkably few cases from the younger neutering age groups, as shown in Table 3. This study has led to early neutering practices in many countries, in particular the USA where it is commonplace to per form neutering surgery as early as 12 weeks of age.
<u>Age of neutering and relative risk of the development of mammary neoplasia in the bitch compared to intact individuals and number of cases from which statistics are derived.</u> From Schneider et al. (1969)
Age at neutering Relative risk of mammary neoplasia
<span style="color: #FF0000">n</span>
Before 1st season 0.5%
<span style="color: #FF0000">n=1</span>
Between 1st and 2nd seasons 8%
<span style="color: #FF0000">n=3</span>
2 or more seasons 26%
<span style="color: #FF0000">n=20</span>
2 or more seasons but <30months old 6%
<span style="color: #FF0000">n=2</span>
2 or more seasons but >29 months old 40%
<span style="color: #FF0000">n=18</span>
<span style="color: #FF0000">n: number of corresponding cases in study from which statistic is derived</span>
No wonder so many subsequent articles which list the percentages (but not the n number) also go on to state that the risk is very low if bitches are spayed before 30 months.
There are a number of other risk factors which increase in spayed females eg, cardiac tumours, osteosarcoma, bladder and urethral tumors, hypothyroidism, acute pancreatitis, urinary incontinence ... (this is not meant to be a comprehensive list - if you wish references, most have been discussed in earlier threads on this topic) BUT mammary tumours are the most common tumour in female dogs:
In entire bitches, the ratio of benign:malignant tumours is approximately 50:50. Neutering, however, appears to preferentially reduce the incidence of benign mammary neoplasia. Therefore, while the overall incidence of mammary cancer is considerably less in neutered bitches, the likelihood of malignancy is greater than 50 per cent.
The right time to spay YOUR dog is something you should discuss with your vet, taking into consideration the breed of the dog & your ability/desire to manage your dog through heat cycles; it is much better to spay early than have an accidental litter (you <u>can</u> choose to do a spay~abortion: this should be done as early as possible)