Teat injuries are frequent in dairy cattle. Removal of a large internal (covered) lesion precludes the closure of the teat mucosa. If left to heal by second intention, collapse of the teat cistern and adhesions between the teat walls will most likely occur. Different tissues and grafting materials have been used to reconstruct teat mucosa. At this time, each technique developed has many post¬operative complications and carries a guard prognosis for return to normal function of the teat.
In our study we hypothesized that polycaprolactone (PCL), a new tissue engineered polymer, will promote better healing when grafted over an induced teat mucosa defect if compared with a defect left to heal by second intention. The objectives of our study were to evaluate the biocompatibility of the polymer with cow’s mammary tissue and to compare the healing of an induced teat mucosa defect covered by PCL with the healing of a defect left to heal by second intention.
Four cows allowing for a total of 16 teats were used in this study. Each teat was randomly assigned to a treatment group (group l=defect left to heal by second intention and group 2=defect cover by a PCL polymer graft). With the cow in lateral recumbency, a 3 cm incision was made to expose the teat cistern mucosa where a circular 8mm defect was created. The defect was covered or not with the PCL graft and the incision was closed. The healing of the defect was followed weekly by ultrasound and bi-weekly by theloscopic evaluation. The cows were euthanized 28 days after surgery and the teats were retrieved for histopathologic evaluation.
No statistically significant differences were found between groups regarding the degree of inflammation, fibroplasia and epithelialisation. The defects left uncovered were smaller 28 days after surgery and were covered mostly by a stratified epithelium. The defects covered by the PCL polymer graft were mostly covered by a squamous epithelium. Adhesions and exuberant granulations tissues were present over the defect for both treatment groups. No statistically significant differences were found between groups regarding the ultrasound and theloscopic findings. However, in both groups, the teat wall and the defect sizes during ultrasonic evaluation were statistically significantly thicker at 21 and 28 days if compared with measurements obtained at Day 0, 7 and 14.
The biocompatibility of the PCL polymer with cow’s mammary tissue is considered to be poor. However, many factors other than the material itself can explain the results obtained in this study. The exposure to milk secretions and the surgical technique might have predisposed the surgery site to inflammation and adhesion formation. The small number of animal used in this study might have influenced negatively our results. Finally, the processing of the polymer into 8 mm sheet might not have been adequate.
In conclusion, in a dry cow model, it is not recommended to cover a 8 mm mucosal defect with a 5 µm of thickness PCL sheet. Pre-seeding the polymer with epithelial cells and using it for larger defects in lactating cows needs to be further evaluated to determine if PCL polymer can be of any use in teat and udder surgery.