Did you know your horse's fat cells are described in terms of how they "express themselves"? British researcher Melissa Packer of the University of Liverpool thinks that the characteristics of abdominal fat cells may have a lot to do with which horses survive colic surgery and which ones do not.
Packer collected abdominal fat samples from around 230 horses as they were undergoing colic surgery. She then looked at the "expression" of various cytokine genes in the fat tissue to see which cytokines were being produced. Cytokines are proteins released by cells that have a variety of functions, including immune functions such as triggering inflammation and responding to infection. Fat tissue has been shown to contain a raised level of cytokines.
Each of the 230 horses was then followed over the next two years, with data gathered on post-operative complications and survival following colic surgery. Each horse's owner was contacted every three months for the first year to check up on the horse's progress, and then every six months in the second year.
After analyzing fat samples from 78 horses, Packer found a significant and positive association between the expression of a cytokine called MCP-1 and an increased rate of post-operative mortality. In other words, in horses with MCP-1 in their abdominal fat, the chances were high that the horse would not live.
"The relationship between MCP-1 and mortality from colic opens up the possibility of using it as a diagnostic tool when examining horses. Such a test would be a useful additional tool for vets when dealing with horses that are seriously ill and where it is uncertain whether they would survive additional surgery, or whether it is better to consider euthanasia," said Packer.
Testing for the genetic expression of MCP-1 would take too long at present, as the DNA must first be amplified using a technique called polymerase chain reaction (PCR). However, further developments in designing a test to detect circulating levels of MCP-1 in the blood could be of great benefit.
Packer found no relationship between post-operative mortality and the other cytokines she looked at: leptin, adiponectin, TNF, MIF, NGF and IL-6.
During her research, Packer also looked at the relationship between various cytokines and the BMI (Body Mass Index) of horses. The BMI of each horse was calculated by using data on their age, species, breed, height and weight. Expression of equine leptin from retroperitoneal fat increased significantly with increasing BMI but was not associated with increased post operative mortality.
She expected to find a higher genetic expression of MCP-1 in the fat tissue of obese horses as they would be expected to have a lower survival rate from colic surgery. However, she found the opposite: the expression of the MCP-1 genes was lower in obese horses. Packer hypothesises that this could be because obese horses already have the maximum level of MCP-1 in their blood, so were no longer producing the cytokine within their fat cells at the time of sampling.
Packer now hopes to look at MCP-1 levels in blood to confirm this theory. She has already collected and frozen blood samples from each of the 230 horses involved in the study, so hopes to analyze these samples in the near future.
Packer is currently applying for funding for a PhD to continue research into this area. "Obesity is a major health issue for horses, so it is vital that we have a better understanding of the impact obesity has on colic surgery survival rates," said Packer.
About the researcher: Melissa Packer BVet Med CertES(Soft Tissue) MRCVS is a Senior Clinician in Equine Gastroenterology at the University of Liverpool's Philip Leverhulme Equine Hospital. Her research was funded by The Horse Trust, a leading equine research funding agency in Great Britain.