Early age altering of kittens (Proceedings)

While elective gonadectomy is one of the most common veterinary surgeries performed in North America, little data exist to suggest the optimal age (Kustritz 2007). Prepuberal gonadectomy refers to gonadectomy before the onset of puberty, which may occur in female cats between 4 and 21 months of age and in male cats between 8 and 10 months of age. Early age altering (EAA) refers to gonadectomy between 6 and 16 weeks of age and is more commonly practiced as veterinarians gain experience with pediatric anesthesia and surgery. EAA is one useful approach for control of pet overpopulation as it enables shelters and pedigreed breeders to perform pre-adoption altering and avoids the risk of owner non-compliance with altering contracts. Increasingly, it is recognized there are also health benefits to EAA.

Health Issues

Objections to EAA have included concerns about effects on growth, increased femoral fracture risk, obesity, behavioral changes, increased disease risk, and safety of anesthesia and surgery in pediatric patients.

Testosterone and estrogen assist maturation of the physes in long bones. Growth stops when physeal closure occurs. Intact cats have distal radial physeal closure at 1 year of age or older. Cats altered at 7 weeks and 7 months of age had distal radial physeal closure about 8 weeks later than intact cats (Stubbs, Bloomberg et al. 1996; Root, Johnston et al. 1997). The effect of this delay in physeal closure is unknown, but adult size in cats is not significantly affected by age of altering. It has been suggested that delayed physeal closure may predispose cats to Salter fractures of the femoral capital physes. The femoral capital physis normally closes between 7.5 and 10 months of age. Other risk factors for this type of fracture include obesity and gender/reproductive status (neutered male) (McNicholas, Wilkens et al. 2002). The risk of fracture would be the same for cats altered at any age that results in delayed physeal closure, not just EAA cats. These fractures appear to be rare in the altered cat population. One large study failed to find any association between EAA and physeal fracture risk in cats (Spain, Scarlett et al. 2004).

Obesity is a multifactorial problem involving diet, exercise, age and other factors. Altered cats have a lower metabolic rate than sexually intact cats regardless of the age at gonadectomy. Altered male cats require 28% less calories than intact male cats and altered female cats require 33% fewer calories than intact female cats (Root, Johnston et al. 1996). Clients should be counseled on the dietary and exercise needs of altered cats to avoid obesity.

Compared to altered cats, sexually intact cats show less affection to humans and more aggression to other cats. One study has shown that EAA male cats are less aggressive to vets, and exhibit fewer problems with urine spraying (Stubbs, Bloomberg et al. 1996). Other long term studies have shown there is no difference in the prevalence of significant behavior problems based on age at altering (Spain, Scarlett et al. 2004; Wright and Amoss 2004).

Lower urinary tract disease in cats is a diverse collection of conditions caused by a wide variety of factors such as diet, water intake and stressors. The diameter of the male urethra is no smaller in EAA cats than in intact cats (Root, Johnston et al. 1996). Age at altering does not influence risk of urinary tract disease; in fact, one study showed a lower risk of urinary tract obstruction in EAA male cats (Spain, Scarlett et al. 2004).

Several long term studies have been performed to assess health risks of EAA. These studies confirm that EAA is not associated with any increased risk of disease, but rather is associated with a lower risk of some diseases, such as asthma, gingivitis, mammary carcinoma (Howe, Slater et al. 2000; Spain, Scarlett et al. 2004; Overley, Shofer et al. 2005).

Anesthesia and Surgery

Pediatric patients have unique perioperative, anesthetic and surgical issues (Kustritz 2002). Kittens should have a complete physical exam as well as the first vaccination and treatment for parasites before surgery; postpone surgery if any illness or abnormality is found (including cryptorchidism). Anesthesia and surgery do not affect response to vaccination so that kittens can be vaccinated at the same time as surgery if required (Levy, Reese et al. 2006).

With the use of safe and effective techniques, it has been shown that EAA does not increase morbidity or mortality associated with anesthesia and surgery (Aronsohn and Faggella 1993). In fact, kittens altered at less than 12 weeks had lower postoperative complication rates than those altered at over 23 weeks of age in one study (Howe 1997). Surgical benefits of EAA include less bleeding, improved visualization of organs, shorter surgery times and more rapid recoveries.

Pediatric patients distribute and metabolize drugs differently, so the clinician must be careful with drug selection and doses. Weigh each kitten to the nearest 100 grams and calculate drug doses carefully. Bear in mind that renal and hepatic function does not reach adult levels until about 4 months of age. Certain anesthetic concerns must be addressed:

• Cardiac output is rate dependent in neonates; beware of bradycardia (<150 bpm); use glycopyrrolate to prevent or treat

• Maintenance of breath rate is important as neonates have limited ability to respond to elevated CO2 in blood or tissues and have little O2 reserves in the lungs, yet they have high O2 needs

• Use anesthetic equipment with minimal dead space and resistance such as a Bain circuit

Hypothermia occurs easily due to the greater surface area to volume ratio of the neonate, less subcutaneous fat and reduced ability to shiver. Hypothermia can cause bradycardia and prolonged recovery from anesthesia. The prep, surgery and recovery areas should be kept warm. Ensure kittens are never placed on cold metal surfaces. Use warmed towels, circulating water blankets or other methods to maintain body temperature. Plastic "bubble pack" wrapping is also useful for maintaining warmth. Warm the surgery prep solutions, and replace alcohol with sterile saline. Rectal temperature should be monitored during surgery and post-operatively.

Hypoglycemia occurs easily in neonates due to smaller hepatic glycogen reserves, so patients should not be fasted for more than 2 to 3 hours before anesthesia. Water should never be withheld. Within 1 hour of recovery, patients should be offered a small meal. Kittens unwilling to eat after 1 hour or more can be given oral dextrose to prevent hypoglycemia.

Certain surgical concerns must also be addressed. Meticulous hemostasis is necessary as tissues are more friable than in adults; handle tissues gently. For males, perform closed castration via a single or double scrotal incision, ligate the spermatic cord with absorbable suture or use hemostatic clips. Leave the scrotal incision open. For females, the ovariohysterectomy technique is the same as for a mature cat. Close the skin with subcuticular sutures or tissue adhesive and avoid skin sutures. Note that serous fluid in the abdomen of neonates is normal.

Equipment suitable for EAA is simple, and includes:

• Cuffed/noncuffed endotracheal tubes, 2-3.5 mm

• Clear, snug face mask

• Kit with small surgical instruments

• Stainless steel hemostatic clips for ligation if desired

• Absorbable suture material, such as 4-0 or 5-0 Vicryl® (Johnson & Johnson; New Brunswick, NJ) or chromic gut; nylon may be used for closure of linea alba

Certain anesthetic drugs should be avoided in pediatric patients. Xylazine may cause bradycardia and decreased cardiac output. Thiobarbiturates require IV administration. These drugs are also protein-bound, and neonates are easily saturated as they have lower plasma protein levels than adult cats.

Stress and anxiety may lead to unpredictable results of pre-medication and anesthesia. Decrease stress by keeping litters together before surgery in a warm, quiet environment, minimize patient handling, avoid IV injections, and reunite litters of kittens as soon as possible after recovery.

Several drugs and drug combinations are safe and effective for pediatric anesthesia (Faggella and Aronsohn 1993; Howe 1997; Kustritz 2002).Examples include:

• Midazolam (0.22 mg/kg IM), ketamine (11 mg/kg IM), butorphanol (0.2 – 0.4 mg/kg IM), +/- glycopyrrolate (0.011 mg/kg IM)

• Ketamine/diazepam (0.1 mg/kg IM of 1:1 mixture), butorphanol (0.2 – 0.4 mg/kg IM), +/- glycopyrrolate (0.011 mg/kg IM)

• Tiletamine/zolazepam (11 mg/kg IM) for castration of male kittens

• Acepromazine (0.055 mg/kg IM), butorphanol (0.22 mg/kg IM), glycopyrrolate (0.011 mg/kg IM)

• Medetomidine (0.04 mg/kg) + ketamine (20 mg/kg) + buprenorphine (0.02 mg/kg) combined and given SQ; reverse with 0.5 mg/kitten atipamezole IM

• Oxymorphone (0.07 mg/kg IM) may be substituted for butorphanol

Brief mask induction may be required, then maintenance on isoflurane or sevoflurane (intubate spays, use mask for neuters). An injectable only protocol (MKB) has been described for both spays and neuters: medetomidine (40µg/kg), ketamine (20 mg/kg) and buprenorphine (20µg/kg), combined and given subcutaneously (Robertson, Levy et al. 2003). Atipamezole (0.5 mg IM) is given at the end of surgery.

Anesthetic monitoring is necessary and should include assessment of level of anesthesia, color of mucous membranes, Doppler monitoring of heart rate and blood pressure, pulse oximetry, and breath rate. Prolonged recovery is most often due to hypothermia, but can also be caused by residual effects of drugs or hypoglycemia. Corrective measures for prolonged recoveries include warming, using reversal agents if available and providing 50% dextrose or corn syrup for hypoglycemia.

References

Aronsohn, M. G. and A. M. Faggella (1993). "Surgical techniques for neutering 6- to 14-week-old kittens." J Am Vet Med Assoc 202(1): 53-5.

Faggella, A. M. and M. G. Aronsohn (1993). "Anesthetic techniques for neutering 6- to 14-week-old kittens." J Am Vet Med Assoc 202(1): 56-62.

Howe, L., M. Slater, et al. (2000). "Long-term outcome of gonadectomy performed at an early age or traditional age in cats." J Amer Vet Med Assoc 217(11): 1661-1665.

Howe, L. M. (1997). "Short-term results and complications of prepubertal gonadectomy in cats and dogs." J Am Vet Med Assoc 211(1): 57-62.

Kustritz, M. (2002). "Early spay-neuter: clinical considerations." Clin Tech Small Anim Pract 17(3): 124-128.

Kustritz, M. V. (2007). "Determining the optimal age for gonadectomy of dogs and cats." J Am Vet Med Assoc 231(11): 1665-75.

Levy, J., M. J. Reese, et al. (2006). "The effect of anesthesia and surgery on serological responses to vaccination in kittens." J Vet Intern Med 20(3): 759.

McNicholas, W. T., Jr., B. E. Wilkens, et al. (2002). "Spontaneous femoral capital physeal fractures in adult cats: 26 cases (1996-2001)." J Am Vet Med Assoc 221(12): 1731-6.

Overley, B., F. S. Shofer, et al. (2005). "Association between ovariohysterectomy and feline mammary carcinoma." J Vet Intern Med 19(4): 560-3.

Robertson, S., J. Levy, et al. (2003). Comparison of isoflurane and butorphanol with medetomidine, ketamine and buprenorphine for anesthesia of 7-12 week old kittens for surgical sterilization. Association of Veterinary Anaesthetists. Doorwerth, The Netherlands.

Root, M., S. Johnston, et al. (1996). "The effect of prepuberal and postpuberal gonadectomy on penile extrusion and urethral diameter in the domestic cat." Vet Rad & Ultra 37(5): 363-366.

Root, M., S. Johnston, et al. (1996). "Effect of prepuberal and postpuberal gonadectomy on heat production measured by indirect calorimetry in male and female domestic cats." Am J Vet Res 57(3): 371-374.

Root, M., S. Johnston, et al. (1997). "The effect of prepuberal and postpuberal gonadectomy on radial physeal closure in male and female domestic cats." Vet Rad & Ultra 38(1): 42.

Spain, C., J. Scarlett, et al. (2004). "Long-term risks and benefits of early-age gonadectomy in cats." J Amer Vet Med Assoc 224(3): 372-379.

Stubbs, W., M. Bloomberg, et al. (1996). "Effects of prepubertal gonadectomy on physical and behavioral development in cats." J Amer Vet Med Assoc 209(11): 1864-1871.

Wright, J. C. and R. T. Amoss (2004). "Prevalence of house soiling and aggression in kittens during the first year after adoption from a humane society." J Am Vet Med Assoc 224(11): 1790-5.