This study contrasts bone and body development in puppies that were neutered or spayed at 7 weeks of age with puppies that were neutered or spayed at 7 months of age and pets that were allowed to mature naturally to 15 months of age. It has been used to justify the neutering of infant and juvenile pets - but rarely actually read.
The study was funded by The AVMA and the Winn Foundation who saw an "absolute necessity in controlling" pet populations. and were attempting to generate information that would justify infant spay/neuter programs. It is given a scientific title, but is labeled in each page footer as “Pet Overpopulation”.
Despite the bias of its objective, the sponsors were quite disappointed in the results. The bodies of the pets spayed as infants were noticeably different from the ones spayed at 7 months of age and compared to the unspayed control group, neither the pups spayed at 7 weeks of age nor those spayed at 7 months of age developed normally.
The urinary tracts of both pediatric spay/neuter groups never fully developed and their bones never assumed normal conformation.
The authors end their study with this statement:
"The clinical significance of immature external genitalia in the early castrates and the effects of prepubertal gonadectomy on bone strength, urethral development/function and immunocompetence requires further investigation."
In effect they are saying, "Let someone else deliver the bad news".
J Am Vet Med Assoc. 1991 Apr 1;198(7):1193-203.
Gonadectomy in immature dogs: effects on skeletal, physical, and behavioral development.
Salmeri KR, Bloomberg MS, Scruggs SL, Shille V.
Department of Small Animal Clinical Sciences, University of Florida, Gainesville 32610-0126.
In a 15-month study, the effects of prepubertal gonadectomy on skeletal growth, weight gain, food intake, body fat, secondary sex characteristics, and behavioral development were investigated in 32 mixed-breed dogs. Male and female pups from 5 litters were randomly allotted to 3 groups: group I, neuter at 7 weeks (n = 14); group II, neuter at 7 months (n = 8); and group III, sexually intact dogs (n = 10). Growth plate closure was delayed (group I vs group III; P less than 0.000001; group II vs group III, P less than 0.000001) in all neutered dogs, as compared with sexually intact dogs. Growth plate closure was delayed longer (group I vs group II, P less than 0.000045) in dogs neutered at 7 weeks old, compared with dogs neutered at 7 months old. The rate of growth was unaffected by gonadectomy, but the extended growth period resulted in greater final radial/ulnar length in all male dogs and bitches neutered at 7 weeks. Gonadectomy did not influence food intake, weight gain, or back-fat depth. Penile development was immature in the adult group-I males (mean +/- SEM diameter of pars glandis = 11.1 +/- 1.0 mm), compared with adult group-II (16.3 +/- 0.5 mm) and group-III (21.0 +/- 2.2 mm) males. Subjectively, the prepuce and os penis of the group-I males were immature, compared with those of group-II and group-III males. Vulvar development in group-I and group-II bitches was less mature than vulvar development in the sexually intact bitches. Of 7 behavioral characteristics assessed, only general activity and excitability rated differently among treatment groups. All neutered dogs were judged to be more active (group I, P less than 0.004) than sexually intact dogs. Group-I males were judged to be more excitable (P less than 0.02) than group-III males. It was concluded that with respect to skeletal, physical, and behavioral development, the effect of neutering pups at 7 weeks old was similar to that of neutering pups at 7 months old.
PMID: 2045340 [PubMed - indexed for MEDLINE]
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