◊ Experimental Surgery ◊
Experimental surgery in farm animals
The main purpose of this chapter is to present surgical techniques that will be useful to the physiologists, pharmacologists, medical students, animal scientists and other interested in certain biological questions that can be answered only through experimentation on especially prepared animals.
Experimental surgery is an extremely valuable adjunct to certain types of research, in some cases it may be the only way to obtain satisfactory results, however, it is always advisable to keep surgery as minimal as the problems permits.
Farm animals as sheep, goat, cattle, buffalo, camel and horses are used for experimental surgery in veterinary agricultural schools and institutes as well as laboratories and medical schools devoted to study of human health.
The chapter describes some experimental procedure of handling different surgical interventions on goats as a model for experimental surgery and discusses methods.
There are different experimental surgical techniques that are useful for medical authors, animal scientist and author interested in certain biological questions that can be answered only through experimentation on specially prepared animal models.
These include the following selected techniques
1-Surgical cannulation of extra-testicular rete testis (ETRT)
2-Skin cuffing the carotid artery
3-Simplified duodenal (post pyloric) cannulation
1-Surgical cannulation of extra-testicular rete testis
(ETRT) in goat
The rete testis of the goat can be divided into three parts, septal, mediastinal, and extra testicular. The extra testicular rete testis is located outside the testis at its extremitas capitata and forms sac like dilatation up to2mm in diameter mot studies on spermatozoa and fluid collected directly from testis of the conscious goat cleared that there are metabolic difference between testicular and ejaculated spermatozoa that may be the result of the process of maturation.
1-Preparation of the animals
Feed and water were withheld for 24 hours and 12 hours respectively. The animal was positioned on dorsal recumbency. The inguinal, scrotal and perineal regions were clipped and prepared for aseptic surgery.
Epidural administration of xylaxine HCL 2% in dose rate 0.3 mg\kg b.wt. diluted up to 2ml by physiological saline followed by epidural ketamine HCL 5% in dose rate 5 mg\ kg.b.wt.
An 7 cm linear incision was made lateral and parallel to the median and then packed off with sterile saline oaked in sponges (Fig1). a semicircular incision was made through parital vaginal tunica (PVT) in the caudal aspect of the testicle , 2 cm dorsal to the epididymal tail then delivered the testicle through the incision (Fig 2). A small incision was made in the visceral vaginal tunic (VVT) at the distal part of the head of the epididymis. The head of the epididymis was reflected dorsally by careful blunt dissection, the ERT located below the epididymal head. The connective tissue around the ERT was gently teased away to pass a length 2.0 ilk suture behind the tubular part of the ERT. A stab incision in the wall of the ERT was made by 18 gauge needle, a poly ethylene cannula (I D 1 mm and OD 1.5 mm) with a beveled tip was inserted into the lumen and pass distally approximately 8 mm into the mediastinal rete testis. The cannula filled immediately by capillarity action with rete testis fluid then properly placed (Fig 3). The silk was tied around the cannula with surgeons knot to secure it in place. The reflected head of the epididymis was retained to its original site the sutured to the VVT with simple interrupted sutures of 3-0 Dexon.
The testicle was replaced in the vaginal cavity and sutured the PVT with simple interrupted sutures (Fig 4). A small stab incision was made in the caudal aspect of the PVT and other layers of scrotum at the same level to exteriorize of cannula .The scrotal incision was closed in a a simple continuous pattern with 2-0 suture (Fig 5). The cannula was threaded through a small hole in the plastic collecting bottle. The collecting bottle was fixed onto the caudal aspect of the scrotum (Fig 6).
1-Teticle become edematous due to manipulation during operation (anti-inflammatory and anti-edematous drug remove the problem)
2-Sperm clot in the lumen of the cannula causes cessation of fluid flow (flushing of the cannula by warm sterile physiologic saline)
1-Local anti-septic (Povidine iodine)
2-Systemic broad spectrum anti- biotic 5 successive days
3-Suture removed after 8 days
2-Skin cuffing the carotid artery in goat
Many physiologic and pharmacologic investigations in animal models require frequent or continuous arterial blood sampling and blood pressure measurements. Catheterization for these measurement is most often performed in animals given chemicals –restraining agent \(tranquilizers) which alter both physiologic reflexes and pharmacologic responses. . Carotid loops have been used extensively in sheep and goats to provide easy access for pressure measurements and sampling of arterial blood
Preparation of animals
The skin of the jugular farrow and adjacent areas were clipped, scrubbed, and disinfected. The prepared animal was placed in lateral recumbency with the right side upper most.
Diazepam 0.5% in a dose rate of 1 mg\kg IM as a pre-anesthetic medication, after 15 mins, ketamine HCl 5% in a dose rate 3 mg\ kg IM, the after 10 mins xylazine HCl 2% injected slowly IV in a dose rate of 0.1 mg\ kg diluted to a total volume 3 ml with normal saline in the jugular vein opposite the side selected for surgery.
A skin incision 10-12 cm in length was made at the medial margin of sternomustoid muscle (Fig 1). The kin was freed of underlying connections along the length of incision. The external jugular vein was reflected ventrally and its small collateral branches were ligated and severed. The carotid artery and the vagus nerve were raised from their bed with a loop of umbilical tape (Fig 2). A secondary incision 5-6 cm long was made 3-4 cm dorsal to and parallel with the line of the initial incision. The skin and S.C. fasia lying between the two incisions were freed by blunt separation to make a tunnel between each other and producing a 6 cm skin flap (Fig 3). The ventral edge of the initial incision and the dorsal edge of the secondary incision were sutured with interrupted sutures (No. 0 cat gut) (Fig 4). The skin flap was wrapped around the carotid artery and sutured together with interrupted sutures No.0 chromic cat gut. The skin tube containing the carotid loop should be rotated inward and ventrally until the un-sutured edges are visible (Fig 5).
As mentioned before in operation number 1 except that the sutures are left in place until they dissolved and fell off. percutaneous catheterization of the carotid loop has been performed many time without any side effect , clot formation was avoided by continuous flushing of artery by heparinized saline
3-Simplified duodenal (post pyloric) cannulation in goat
Duodenal cannulation of ruminants allowed digestion in the fore stomach to be studied. The easiest part of the intestine to be cannulated is the start of the duodenum, only a short skin incision is needed and this is made immediately behind the ventral end of the second last rib. The duodenal cannulation has been utilized extensively for intestinal transection and permanent diversion of digestion outside the body.
Poly propylene plastic cannula, simply it is a disposable syringe 5 or 10 ml volume, pyrogen free, non-toxic, sterile and ready to use after modification (Fig 2).
Preparation of the animals
Feed and water were withheld for 24 hours and 12 hours respectively before surgery. Animal was positioned on left side. Right paracostal region was prepared for aseptic surgery.
Xylazine HCl 2% was given epidurally at dose rate of 0.3 mg\ kg diluted to 4 ml total volume by sterile physiological saline.
A longitudinal laparotomy about 8 cm length was performed 5-8 cm below the floating ribs (Fig 1). The duodenum was exteriorized then two plastic clamps were fixed to avoid rush of digesta. Purse string suture with 2\0 non absorbable material was done in between the clamps (Fig 3). The duodenal wall was incised (1-1.5 cm) in the center of purse string area, the flanged part of the prepared cannula was inserted through enterotomy site and the threaded suture was tightened, then reinforced with another one (Fig 4). The duodenum was then repositioned to the abdominal cavity, the free end of the cannula was exteriorized from a small stab wound dorsal to the initial one by 2.5 cm (Fig 5). Translocated cannula was secured in (Fig 6) place by pure string suture with No. 1 silk to the skin. The abdominal incision was closed in layers (Fig 7).
As mentioned in operation one
Sampling of digesta was done by removal of the plug from cannula and waiting the free flow of digesta