Effects Of Different Fat Supplements On Fasting-Induced Fatty Liver Disease In Mink

Fatty liver disease is a frequent pathological finding in mink (Neovison vison). The disease is characterized by the accumulation of fat in the liver tissue, which is most often caused by a metabolic dysfunction or by nutritional factors. The onset of the disease can be very rapid, within two to seven days, and leaving very little time for administering treatment to the sick animals. This problem has been compounded by the lack of understanding regarding the mechanism underlying the disease, which at this stage is still unclear. Thus, in order to prevent and relieve fatty liver disease in mink, it is vital to understand in greater depth, the mechanism of the disease and how fatty acid may contribute to this pathological condition needed to be investigated. The specific objective of this study was to investigate the effects of dietary fat and short term fasting on the subsequent development of fatty liver disease in mink.Short term fasting in farming mink induces intrahepatic accumulation of lipids, and therefore, this method was used to induce fatty liver disease in experimental mink. Diagnosis and treatment of the disease artificially induced in mink were tested using the short term fasting model. For treatment, three different sources of dietary fat were examined, and these were chicken oil, fish oil and soybean oil. Following a5-day fasting period, the mink were fed with a diet containing one of the three fats for7,14,21or28days. After that, the levels of liver recovery achieved by these fat-containing diets were determined and compared.The results showed that during the fasting period, the mink showed increased liver size and accumulation of hepatic triacylglycerol. Moreover, increased activities of alanine aminotransferase and aspartate aminotransferase were also evident in the plasma. These changes were indicative of the signs of hepatic dysfunction, which was induced in the animals by short term fasting. During the refeeding period, the livers of the animals gradually recovered, and liver lipids appeared to return to the normal level. The physiological-biochemical blood parameters and lipase activity were examined after refeeding. During the fasting period, free fatty acid levels in plasma of the animals increased, indicating that lipid was being mobilized. The mobilization of lipid caused hepatic lipidosis. Increasing the dietary intake of n-3polyunsaturated fatty acids (PUFA) in fish oil group increased fatty acid oxidation and lowered the deposition of lipid in the liver. Moreover, during the fasting period, the activities of some lipases in adipose tissue tended to increase, but no significant differences were observed among the animals fed with different dietary fats.Analysis of the fatty acid composition showed that n-3PUFA in plasma, liver, subcutaneous fat, intra-abdominal fat increased significantly (PO.05) for the group fed with fish oil, compared to the control group. The content of n-3PUFA was highest in the liver. which probably reduced the deposition of lipid in the liver. These animals also exhibited enhanced oxidation of fatty acid, compared to those fed with chicken oil and soybean oil. Enhanced oxidation of fatty acid helped to reduce lipid deposition in the liver, and therefore protected the liver of the animals (to some extent) from the onset of dysfunctions.Fatty liver can be observed during periods of high stress, such as whelping and weaning in female mink and the furring out period at the beginning of the fall. During these periods the animals may experience a loss of appetite for a few days, causing rapid weight loss and resulting in accumulation of fat within the liver. In order to keep the animals healthy during these special periods, dietary intake of n-3PUFA should be recommended.In conclusion, the results of the present thesis demonstrated that fish oil could promote the oxidation of fatty acid, leading to reduced fat deposition in the livers of mink consuming fish oil as a form of dietary fat. Thus long term consumption of fish oil as part of their diet may protect these animals against liver dysfunction, and reduce mortality associated with hepatic lipidosis. This research finding also provided new insights into the mechanism underling fatty liver disease in mink.