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In addition, intact (not neutered) adult male rats normally secrete fluids from the accessory sex glands that act as an energy source for sperm, contribute to the mobility and viability of sperm, help to lubricate the urethra and clear it of urine prior to ejaculation, and serves as a means of transporting the sperm in the female tract and creating a copulatory plug to help ensure fertilization. Secretions called smegma, composed of oils, moisture, and shed epithelial cells help to keep the glans moisturized. Under normal circumstances the healthy male rat is able to adequately clean the penis and sheath, and prevent the buildup of secretions. However in the aging or ill male rat, or those males with paresis, the ability or flexibility to groom may decline causing these secretions to become firm and large blocking or plugging the urethra. These urethral proteinaceous plugs can interfere with urination and/or lead to infection if not removed. In male rats where an orchiectomy (neuter) has been performed the development of urethral plugs is significantly decreased or eliminated.
The procedure for neutering a male rat is considered, by veterinary surgeons experienced with rats, to be easier, less traumatic, and associated with less morbidity and mortality than performing an ovariohysterectomy on a female rat. (Bennett, Rodents:soft tissue surgery, 2009; Bennett, Soft Tissue Surgery, 2012)
The following descriptions in each section is presented to provide the rat owner with how to prepare their male rat for day of surgery and the type of care, prep, procedure(s), and recovery the veterinarian may follow. There are sections also for home care recommendations and additional comments which may be helpful.
For rats with a history of respiratory illness, or for those rats that are elderly and where the pain and stress of a procedure can further suppress the immune system, it is advisable for the veterinarian to place the rat on an antibiotic with coverage for mycoplasma as a prevention to relapse. The antibiotic should be started a few days prior to surgery and continued until the surgical incision site has healed.
Ideally, a baseline minimal screening (hematocrit, total protein, blood glucose, blood urea nitrogen, urine specific gravity) may be advised preop. However, there is a wide range of normal lab values reported in rats, and depending upon the procedure and age of the rat – unless the rat has a previous health history - it may not always be necessary. (Bruce & Olsen, Ovariectomy, ovariohysterectomy and orchidectomy, 1986)
The pet rat should be brought in a small one level cage or carrier where the rat can be easily observed from all sides of the carrier by the veterinarian and staff. It is helpful to attach a small tag to the carrier with your rat’s name, sex, age, color/markings, type of surgery, as well as your name and a phone number where you can be reached. Also note whether or not the rat can be handled safely. Some rats may become frightened around unfamiliar humans, such as: semi-wild rats, or rats that may have been abused and rescued.
Provide non-ravel cloth (e.g., fleece or t-shirt type material) for bedding, preferably white or light-colored, so that signs of urination or bleeding are easily visible. In addition, provide an extra clean set of bedding if the rat is expected to wait awhile before the surgery (the bedding may become soiled).
A filled water bottle and the rat’s food – including fresh fruit and small treats – should accompany and be accessible to the rat. Note that the water bottle may need to be lowered during the recovery period, if the rat cannot sit up comfortably. In addition it is advisable to include high caloric foods (e.g., pasta, porridge, oatmeal, farina, etc.) in the diet during a few days leading up to day of surgery. Doing so can aid metabolic function, reduce hypoglycemia, and may improve healing time.
Making sure the rat is well hydrated helps to prevent dehydration throughout the perioperative period. Note that the maintenance fluid volume for rats is approximately 100 mL/kg/day. Warmed, IV or SQ, crystalloid fluids (e.g. lactated Ringers or Hartmann’s solutions or normal saline) may be required to maintain hydration perioperatively.
Since rats possess serum atropine esterase, which rapidly hydrolyzes atropine, administering atropine for secretion reduction or for its vagolytic effects may not be that effective. In cases where secretion reduction is necessary, and depending upon the procedure, the veterinarian may elect to use glycopyrrolate. (Bruce & Olson, 2008; Harkness, et al, 2010 )
Preemptive analgesia should be used cautiously in rats. Although it may be desirable to reduce effects of pain upon arousing in recovery, and provide the ability to reduce the percentage of gas anesthetic when giving an opioid such as buprenorphine prior to the anesthetic, both opioids and particularly NSAIDs (such as Metacam or carprofen) are best used postoperatively when blood pressure is more stable and the side effects less. Note, that the use of NSAIDs alone does not require reduction of gas anesthetic. (Flecknell & Richardson, 2009; Bennett, 2012)
Providing oxygenation to the rat prior to intraop (along with providing oxygen intraop and postop) will significantly help prevent hypoxemia and hypocapnia.
Minimizing the area of fur shaved at the site for incision, prepping with warmed surgical scrub such as chlorhexidine and avoiding use of alcohol prep, and providing absorptive towels to prevent the rat from becoming wet will help to decrease development of hypothermia.
It is important for the veterinarian to be prepared for emergencies prior to anesthetizing the rat. Any emergency drugs should be prepared and ready, at the correct dosage.
While some anesthetic agents are not appropriate for use in rats due to an increased risk of anesthetic death, the following are those with the widest margin for safety:
Isoflurane or Sevoflurane are considered the safest and most effective anesthetics for use in rats. The advantage is that each of these inhalation agents permits a quicker induction and recovery, being only minimally metabolized in the liver with the majority being eliminated through exhalation. This is particularly helpful in older rats or those rats with subclinical hepatic issues. While these inhalant anesthetics do have the effect of hypothermia and drying of respiratory mucous membranes, these effects can be countered by the use of a recirculating warm water pad or warm air blanket and monitoring the rat’s temperature, and keeping the rat hydrated, respectively. (Flecknell & Richardson, 2009 ; Girling, 2013)
When administering injectable anesthetic agents those that allow for a specific antagonist to be used when the agents must be reversed quickly provide a better margin of safety. Agents such as xylazine and medetomidine can be reversed with atipamezole. Using either xylazine or medetomidine in combination with Ketamine allows for lower dosage of the drugs to be given, decreasing unwanted side effects. IV or IP administration is preferred over IM or SQ. IV administration allows the effects of the drugs to be seen quickly and for the dosing to be adjusted. Since these substances are irritating to tissue, giving them SQ or IM can result in nerve irritation and/or muscle necrosis at the injection site, as well as self-mutilation, if care is not taken when injecting. Injecting into thigh muscle should be avoided for this reason. A disadvantage of injectable anesthetics is that reversal and recovery take longer because they are required to be metabolized before being eliminated by the body, and the fact that they can cause severe hypotension. (Flecknell & Richardson, 2009)
It is important to prevent hypothermia from developing. Anesthetic agents suppress the body’s ability to regulate temperature. Rats physically have a large body surface area to volume ratio and when inactive due to being sedated or anesthetized they can rapidly become hypothermic. When performing surgery on the rat it is therefore important that it be performed on a recirculating warm water pad, or warm air blanket. In addition, draping the rat as soon as possible while in surgery can decrease heat loss. (Mayer, 2013) While warm water bags and heated pads regulated to 30-35 degrees centigrade (85-95 degrees Fahrenheit) and covered by a towel before placing the rat on it may also be used, this should be done carefully so as not to cause burns to the sedated rat. The temperature should also be carefully monitored throughout the surgery and recovery to ensure that the rat does not become overheated. Hyperthermia in the rat can be just as deadly as hypothermia.
Sperm are produced in the testes and then are transported by a series of ducts until they exit the penis via the urethra.
In male rats, the testes normally descend from the abdomen into the scrotum approximately 15 days following birth, although it is not uncommon for them to descend, in a young male rat, between 4-6 weeks of age. Testes that have not or do not descend may be retained in the abdominal cavity or the inguinal canal. It is important to note that throughout life male rats normally have open inguinal canals with a functional cremaster muscle that allows the testes (testicles) to migrate easily in and out of the abdominal cavity for both protection and temperature control.
The testicles, in male rats, are large in comparison to the size of their body and are oval and smooth in shape. They are contained in two muscular sacs within the scrotum. In addition they have a large pad of epididymal fat as well as a pad of fat on each side of the lower abdomen which aids in preventing herniation into the intestine. Noted also are the large seminal vesicles that aide in partially occluding the internal inguinal ring, and helps to prevent visceral herniation. (Flecknell & Richardson, 2009) (Bennett, Rodents:soft tissue surgery, 2009; Bennett, Soft Tissue Surgery, 2012)
Castration (neuter, orchidectomy) involves the removal of the testicle, epididymis, and part of the vas deferens.
Various techniques and approaches are described, but it must be remembered that in this species the inguinal ring remains open, making it imperative that the vaginal tunic is closed following removal of the testicle. Following proper procedure with each approach can prevent catastrophic intestinal or visceral herniation, tearing of the vaginal tunic or testicular vessels, or damage to the prepuce. In addition it is also important to prevent pulling the testicles to far from the body, in the male rat, when performing surgery so as not to tear the vessels. Inadequate control of subcutaneous vessels and those within the tunics can be cause for incisional and scrotal hemorrhage. (Bennett, Rodents:soft tissue surgery, 2009)
The types of techniques used to perform a castration (neuter, orchiectomy) are the following:
The rat is placed in a dorsal recumbancy (lying on its back) position. The fur is clipped around the scrotum and the penis, and the area is prepped aseptically. The vaginal tunic is incised and the testicle exposed. The ligament of the head of the testis is broken down manually and the spermatic cord is directly clamped and ligated using either the 2- or 3-clamp technique. Absorbable suture material (e.g., polyglactin 3/0 or 4/0 ) should be used for the ligature. The stump is checked for bleeding before being replaced into the tunic, which must then be closed with a single encircling, transfixing or cruciate ligature, depending on the preference of the surgeon. Again this should be an absorbable ligature. The subcutis and skin are then closed, with preference by veterinarian, using fine intradermal sutures for the skin to reduce the likelihood of interference by the rat.
Closed technique (applicable to scrotal and prescrotal approaches).
The rat is also placed in a dorsal recumbancy (lying on its back) position. The fur is clipped around the scrotum and penis, and the area is prepped aseptically. In closed technique the vaginal tunic is not incised. The testicle is exteriorised while still within the tunic, which is clamped and ligated along with the spermatic cord and vessels as described above in the open technique. The closed technique has the advantage that the tunic is not entered, therefore there is no communication with the inguinal ring or abdomen, and less risk of contamination (although if proper aseptic technique is employed this should not be a concern with either open or closed castration).
*Note that using the closed technique may provide a slight advantage in terms of anesthetic time as there is no need to ligate the tunic separately, though this largely comes down to preference of the veterinary surgeon.
A small area of the cranial scrotum is surgically prepared. Minimal clipping is needed. The incision is placed directly over the scrotum. This technique can be performed with either a single central incision through which both testicles are removed or one incision over each testicle. Again this comes down to the veterinary surgeon’s preference. A single incision is theoretically less traumatic; however a larger incision can be required in order to manipulate both testicles through it. The preference can also be for 2 incisions, which are tiny, right at the cranial end of each scrotal sac. Performing 2 incisions rather than through a single incision can make the approach quicker with less manipulation to both testicles, therefore reducing anesthetic time.
Precrotal approach –
The caudal abdomen is clipped and surgically prepared, and a single incision is placed slightly to one side of the midline (to avoid trauma to the penis), just cranial to the scrotum. Both testicles are manipulated through this single incision.
Abdominal approach –
The rat is placed in a dorsal recumbancy (lying on its back) position. The abdomen is clipped (of fur), prepped and prepared aseptically, and as the inguinal ring remains open in this species, the testicles can be accessed via a caudal laparotomy incision and traction on the spermatic cord.
Abdominal castrations may be favored by some vets, in the same way as ovariectomies. The theory is that it causes less soft tissue trauma. However, this may just be preference based since abdominal incision in and of itself does not appear less traumatic than 2 tiny incisions to the scrotum.
Abdominal castration is used primarily in congenital conditions of cryptorchidism, where the teste or testes fail to migrate freely into the scrotum but remain in the abdomen.
The disadvantage to abdominal castration are that there are greater risks if the rat chews the wound, more heat loss due to having the abdomen open and a larger surgical field, as well as a 3 layer abdominal closure that would be needed, all adding to the anesthetic time….
For any of the above techniques the following closure material may be utilized based on veterinary preference:
Absorbable suture used to close muscle (as in abdominal technique), and the closing of the skin may be done with non-absorbable sutures, surgical adhesive. (Bennett, Rodents:soft tissue surgery, 2009; Bennett, Soft Tissue Surgery, 2012; Flecknell & Waynforth, 1992; Harkness, et al, 2010; Mayer, 2008)
A mention, infrequent, drawback to the scrotal technique, which might be alleviated by an abdominal approach, is that due to the rat being low to the ground, the incision site does tend to get urine on it, which can lead to the potential of scrotal abscesses. For this reason a course of an antibiotic, postoperatively, may be considered whether there is any prior respiratory disease or not.
Continue oxygen and supplemental heat and monitor for and correct any signs of hypoxia, hypothermia and/or hyperthermia.
Turning and repositioning the rat approximately every 10 minutes, until crawl reflex returns, will help to stimulate respirations during recovery and reduce the chance of pulmonary congestion developing.(Bruce & Olson, 1986; Girling, 2013)
Warmed, IV or SQ, crystalloid fluids (e.g. lactated Ringers, Hartmann’s solution, Normal saline) should be continued or instituted if recovery is prolonged, to prevent dehydration, until animal is drinking and eating on its own.
Once the righting reflex returns the rat can be placed in a small cage or carrier, again on non-ravel light colored cloth or light colored paper towels with provision for continued warmth and monitoring.
Encourage oral food and water intake upon being recovered from anesthesia. Small treats, fresh fruit or baby foods may be more welcome to the rat before moving to pelleted or block food.
Monitor rat to ensure the ability to urinate and defecate has returned.
Managing pain in the rat with analgesics such as with the use of opioids, buprenorphine or butorphanol and/or with NSAIDs such as meloxicam or carprofen can help aid in recovery and reduce the chance that the rat will bother the incision site.
Antibiotics should be continued or initiated if the rat has underlying illness , or in the event aseptic technique has not been maintained, or in the case of developing infection.
Provide and continue antibiotic if necessary. Remove litter and substrate. Use paper towels or non-ravel cloth (e.g., felt or t-shirt type material) for bedding in cage.
Monitor incision site closely for infection or wound disruption for at least 72 hours.
In the event the rat has poor appetite and/or has not defecated or urinated by the morning following the day of surgery notify veterinarian!
Return to veterinarian for wound recheck in the event of any untoward, or unusual signs noticed with healing, or for suture removal when instructed to do so.
An Elizabethan collar should only be applied as a last resort since this can prevent the rat from holding its food when trying to eat or drink from a water bottle.
No diet restriction. Free access to food and water should be provided.
It can take up to a few weeks for testosterone level to decrease appreciably and therefore may take from 1 to 2 weeks for sexual activity to cease. Mounting may still persist in those male rats that previously mated with female rats. Pet owners are advised not to place the male back in with a female cage-mate immediately after surgery due to the presence of viable sperm that can still be present where the epididymis remains. References citing the timeline for post operative viable sperm being present in the remaining epididymis post neuter, in rats, vary greatly from 8 days to 8 weeks post-op. Anecdotally, waiting 2-4 weeks post-op before placing a neutered male with an intact female has not resulted in any known pregnancies. However, as noted in Bennett, Rodents:soft tissue surgery, 2009 and Bennett, Soft Tissue Surgery, 2012, viable sperm has been found to be present in the remaining epididymis in n rodents for up to 6 to 8 weeks following castration. A time frame of 6 weeks post neuter prior to placing a male rat with an intact female rat is most commonly practiced by pet rat owners.
Posted on December 28, 2016, 14:17,
Last updated on February 1, 2017, 20:14