Reproductive Surgery In the Pig
Pet pigs have established themselves as a popular but unusual pet. They are generally more intelligent than a dog and relatively easy to train. Pigs kept in a loving environment present with few behavioural problems. However, puberty and its subsequent reproductive requirements can present with unpleasant and potentially dangerous behavioural traits. Pigs come well armed with 4 knives (very sharp knives) in their mouths, a powerful neck and bite and even pet varieties can weigh 100 kg and may out run most humans when provoked.
When negotiating with a pig, it is always good to remember Churchill’s comments that “dogs look up to you, cats look down at you but pigs look you straight in the eye”.
All non-breeding house boars should be castrated. The animal is generally fine until 2 years of age but after this he becomes ‘male’ and dominant and his tusks rapidly develop. Castration is the only answer. Chemical castration methods are being developed, whether these will be applicable for use in pet pigs has yet to be explored. The ideal time for castration is 10-14 days of age when the operation can be carried out without anaesthesia and relatively painless with minimal fuss. Over the years we have castrated many hundreds of pigs without any serious consequences. Castration of the mature pig demands surgery and a general anaesthetic. Castration over the age of 3 weeks has to be carried out by a veterinary surgeon and under this age only an owner who has received training from a vet should castrate their piglets. Only a vet should castrate a piglet with a scrotal hernia.
The sow/gilt can present with a variety of behavioural ‘problems’ that we associate with her reproductive cycles. The sow cycles every 21 days (18-24) and the signs of oestrus can be quite bizarre – off feed, slight temperature, vulval discharge, rubbing, searching, mounting of objects including children and a change in aggression level and loss of house training are all seen regularly. These ‘problems’ can be readily resolved through spaying (ovariohysterectomy) of the sow/gilt.
Spaying of the pig presents with few problems, but being an unusual surgical case, presents the vet with some anxiety and apprehension. The pig’s heart is relatively small to the body size and the pig is prone to very noisy panic attacks when restrained. Some pigs are sensitive to halothane resulting in malignant hypothermia which is potentially fatal. However, this is more of a problem in commercial breeds – Pietrain, Large White, Landrace for example. If this is of concern a blood sample or other body tissue, for example, a hair sample can be taken and the pig tested for the presence of the specific gene.
The surgical procedure
If the surgery is elective, it may be necessary to get a movement licence before moving the pig to the surgery.
The pig is starved for 12 hours prior to surgery and water removed 6 hours before surgery. Note the pig is very prone to gastric ulceration which can start within 24 hours of not eating.
Depending on the pig, pre-medication can start at home with the administration of acepromazine maleate oral tablets provided via a small apple or chocolate bar at a rate of 1-2 mg/kg. Alternatively, the pig can be pre-medicated with 0.1 mg/kg acepromazine maleate injection intramuscular. Intramuscular injection of a combination of ketamine (20mg/kg) and xyalzine (2 mg/kg) has proven to be extremely good at knocking the pig down.
Stresnil (azaperone) is a sedative used commercially in pigs (not available in the USA), however, while it is good for calming sows at mixing and farrowing, It is unsuitable as a pre-medication as the pig will go into an excitable phase on handling making intravenous injection difficult/dangerous.
Note with many sedatives, penile prolapse (paraphimosis) can occur and owners need to be warned that this can be permanent.
In the USA a convenient method of sedation is using an intramuscular injection of Telazol® - xylazine-ketamine mixture (“TKX”). (Zoiletil in Australia) `Reconstitute powdered Telazol® with 250mg xylazine (2.5ml) and 250mg ketamine (2.5ml). Dose at 1ml/25-35kg.
Alternative could be intramuscular injection of xylazine 0.5-2.2 mg/kg IM and Telazol® 3-6 mg/kg IM.
Anaesthesia is achieved using thiopental sodium intravenous (approximately 10 mg/kg to effect) using an ear vein. The pig should be restrained at all times. While the pig may squeal, the easiest and less stressful technique for both pig and operator is the snout restraint.
The sedated pig’s ear veins are raised by applying pressure at the base of the ear. Using a surgical swab the ear veins are visualised. A needle (butterfly catheter) is inserted – in the larger Vietnamese pigs an 18 guage needle is used. Draw back is not performed as the ear vein normally collapses. Injecting a very small amount of anaesthetic will indicate if the needle is properly placed. Note, a large amount of barbituate injected into the perivascular tissues can lead to a degree of necrosis and potentially permanent damage to the ear.
Once the pig is anaesthetised, anaesthesia is maintained using isoflurane on a circle anaethetic machine. Intubation of the pig is more complex than in the dog as the larynx is anatomically difficult to visualise and locate. Masking poses a risk of not achieving a good seal. The technique of intranasal intubation can be utilised.
A 90 kg pig will take a 9 mm endotracheal tube
A 60 kg pig will take a 7 mm endotracheal tube
A 30 kg pig will take a 5 mm endotracheal tube
The endotracheal tubes and Y piece attached to the circle
Once inserted with a twisting action past the nares, the cuff can be inflated and the mouth closed with tape. The pig will then breathe normally through the nose. Anaesthesia can be easily maintained using this technique.
Open castration is performed using a single incision midline. The testes are moved towards the midline and removed. The midline incision is closed.
Ventral midline incision is made. After 6 months of age the uterus is quite large and freely mobile. The removal of the ovaries and uterus is similar to that of the bitch. However, note there is a large uterine middle blood vessel which requires separate ligation. The broad ligament often haemorrhages profusely and separate ligation or cauterisation will be required. The cervical/uterine horn is thick and meaty and transfixation is required. There is less haemorrhage if the pig is spayed while not is oestrus.
Sedatives and barbiturates must be used with caution in a caesarean section as they will cause sedation and anaesthesia in the piglets which could reduce their viability. Propofol (2-5 mg/kg) induction, may be a good alternative
The surgical incision is made in the flank parallel to and well above the mammary glands. This area has less fat than elsewhere and avoids healing problems associated with a midline lesion which can be infected by piglet suckling actions and poor aeration of the wound by the large mammary glands. Once the piglets are born and re-vitalised they can be given water and a small amount of whiskey and kept warm until mother is capable of looking after them. Only once any milk/proteins are consumed does the stomach’s ability to absorb colostrum start to reduce. Delaying the first suckle for 3-4 hours with adequate nursing has not influenced preweaning mortality.
Pain relief using ketoprofen 3 mg/kg or butorphenol . Note phenylbutazone can not be used in farm animals and pet pigs fall into this category.
Post-operative antibiotic cover provided using amoxycillin 7-10 mg/kg. Tablets may be provided. These can be relatively easily administered using apples. Partially core an apple, place the tablets into the apple and replace the core. Feed to the pig who will normally eat with relish.
While under anaesthesia it may be a good time to cut any enlarged tusks, examine the pigs teeth, check ears for mange mites and trim feet.