[gemy]

IMO there is no overwhelming health reason to neuter a dog before 6months old. Furthermore in the case of Yorkies, I would want to wait to insure all adult teeth are in and then of course to see how many baby teeth are still present. Then you can combine teeth extraction with a neuter. And beyond that I want to wait until the growth plates close, which is easily verified by a lateral Xray view of the Tibia.

While the article below is geared towards the Canine Athlete it is easily understandable and for the most part applicable to the regular kind of pet owner.


The timing of a neuter or spay, is best done through intelligent discussion between you and your vet. An informed pet owner does their research up front, and enters into this discussion with their vet with some understanding of the issue(s) involved.


EarlySpay-Neuter Considerations for the Canine Athlete

© 2005 Chris Zink DVM, PhD, DACVP
http://www.caninesports.com/SpayNeuter.html

Those of us with responsibility for the health of canine athletes need tocontinually read and evaluate new scientific studies to ensure that we aretaking the most appropriate care of our performance dogs. This article providesevidence through a number of recent studies to suggest that veterinarians andowners working with canine athletes should revisit the standard protocol inwhich all dogs that are not intended for breeding are spayed and neutered at orbefore 6 months of age.

Orthopedic Considerations

A study by Salmeri et al in 1991 found that bitches spayed at 7 weeksgrew significantly taller than those spayed at 7 months, who were taller thanthose not spayed (or presumably spayed after the growth plates had closed).(1)A study of 1444 Golden Retrievers performed in 1998 and 1999 also found bitchesand dogs spayed and neutered at less than a year of age were significantlytaller than those spayed or neutered at more than a year of age.(2) The sexhormones, by communicating with a number of other growth-related hormones,promote the closure of the growth plates at puberty (3), so the bones of dogsor bitches neutered or spayed before puberty continue to grow. Dogs that havebeen spayed or neutered well before puberty can frequently be identified bytheir longer limbs, lighter bone structure, narrow chests and narrow skulls.This abnormal growth frequently results in significant alterations in bodyproportions and particularly the lengths (and therefore weights) of certainbones relative to others. For example, if the femur has achieved itsgenetically determined normal length at 8 months when a dog gets spayed or neutered,but the tibia, which normally stops growing at 12 to 14 months of age continuesto grow, then an abnormal angle may develop at the stifle. In addition, withthe extra growth, the lower leg below the stifle likely becomes heavier(because it is longer), and may cause increased stresses on the cranialcruciate ligament. In addition, sex hormones are critical for achieving peakbone density.(4) These structural and physiological alterations may be thereason why at least one recent study showed that spayed and neutered dogs had ahigher incidence of CCL rupture.(5) Another recent study showed that dogsspayed or neutered before 5 1/2 months had a significantly higher incidence ofhip dysplasia than those spayed or neutered after 5 1/2 months of age, althoughit should be noted that in this study there were no standard criteria for thediagnosis of hip dysplasia.(6) Nonetheless, breeders of purebred dogs should becognizant of these studies and should consider whether or not pups they bredwere spayed or neutered when considering breeding decisions.

Cancer Considerations

A retrospective study of cardiac tumors in dogs showed that there was a 5 timesgreater risk of hemangiosarcoma, one of the three most common cancers in dogs,in spayed bitches than intact bitches and a 2.4 times greater risk ofhemangiosarcoma in neutered dogs as compared to intact males.(7) A study of3218 dogs demonstrated that dogs that were neutered before a year of age had asignificantly increased chance of developing bone cancer.(8) A separate studyshowed that neutered dogs had a two-fold higher risk of developing bonecancer.(9) Despite the common belief that neutering dogs helps prevent prostatecancer, at least one study suggests that neutering provides no benefit.(10)There certainly is evidence of a slightly increased risk of mammary cancer infemale dogs after one heat cycle, and for increased risk with each subsequentheat. While about 30 % of mammary cancers are malignant, as in humans, whencaught and surgically removed early the prognosis is very good.(12) Luckily,canine athletes are handled frequently and generally receive prompt veterinarycare.

Behavioral Considerations

The study that identified a higher incidence of cranial cruciate ligamentrupture in spayed or neutered dogs also identified an increased incidence ofsexual behaviors in males and females that were neutered early.(5) Further, thestudy that identified a higher incidence of hip dysplasia in dogs neutered orspayed before 5 1/2 months also showed that early age gonadectomy wasassociated with an increased incidence of noise phobias and undesirable sexualbehaviors.(6) A recent report of the American Kennel Club Canine HealthFoundation reported significantly more behavioral problems in spayed and neuteredbitches and dogs. The most commonly observed behavioral problem in spayedfemales was fearful behavior and the most common problem in males wasaggression.(12)

Other Health Considerations

A number of studies have shown that there is an increase in the incidence offemale urinary incontinence in dogs spayed early (13), although this findinghas not been universal. Certainly there is evidence that ovarian hormones arecritical for maintenance of genital tissue structure and contractility.(14, 15)Neutering also has been associated with an increased likelihood of urethralsphincter incontinence in males.(16) This problem is an inconvenience, and notusually life-threatening, but nonetheless one that requires the dog to bemedicated for life. A health survey of several thousand Golden Retrieversshowed that spayed or neutered dogs were more likely to develophypothyroidism.(2) This study is consistent with the results of another studyin which neutering and spaying was determined to be the most significant gender-associatedrisk factor for development of hypothyroidism.(17) Infectious diseases weremore common in dogs that were spayed or neutered at 24 weeks or less as opposedto those undergoing gonadectomy at more than 24 weeks.(18) Finally, the AKC-CHFreport demonstrated a higher incidence of adverse reactions to vaccines inneutered dogs as compared to intact.(12)