Vitamin E requirements of adult domestic cats (Felis catus) fed diets containing high levels of fish oil : a thesis presented in partial fulfilment of the requirement for the degree of Master of Nutritional Sciences at Massey University, Palmerston North, New Zealand

Abstract

The vitamin E (α-tocopherol) requirement of adult cats fed diets containing high levels of fish oil was investigated. Thirty-two (16 male, 16 female) adult domestic cats (Felis catus) were randomly allocated to four groups according to sex and fed one of four experimental diets (A, B, C, and D) for 126 days. The cats were housed in large outdoor pens in groups of 8 cats. Diets A, B, C and D contained approximately 300 g of fish oil per kg diet dry matter and were supplemented to contain 0, 5, 10, and 15 IU DL-α-tocopheryl acetate per g added fish oil per kg diet, respectively. The diets were provided ad libitum with water being available at all times. Food intake was measured daily and body weights were measured at weekly intervals. Blood samples were taken from the jugular vein of each cat at bi-weekly intervals during the study. Blood samples were analysed for plasma α-tocopherol, red blood cell H₂O₂ (4 and 2 %) haemolysis, the ferric reducing ability of plasma, plasma lipid peroxides, plasma triglycerides, alkaline phosphatase and whole blood lymphocyte proliferation. All cats remained healthy throughout the study except one female cat who was removed after 3 weeks due to poor food intake. The four diets were analysed and found to be free of peroxides. The average daily metabolisable energy intake of the cats on diet A, B, C and D at the end of study were similar and were 289, 261, 256, and 267 kJ·kg⁻¹ body weight, respectively. No clinical signs of vitamin E deficiency were observed in any of the cats. The plasma α-tocopherol concentrations of the cats in the four groups at the start of the study were not significantly different between the four groups (mean ± SEM, 3.4 ± 0.2 μg-ml⁻¹). When the cats were fed diet A (unsupplemented), the mean plasma α-tocopherol concentration remained relatively low and the RBC 4 % H₂O₂ haemolysis remained high, while the RBC 2 % H₂O₂ haemolysis decreased consistently. Plasma lipid peroxides remained relatively low throughout the study. The ferric reducing ability of plasma status was compromised in the cats on the unsupplemented diet. There was no significant (P < 0.05) difference in any of the response parameters measured amongst the cats fed diets B, C and D except for the RBC 4 % H₂O₂ haemolysis of the cats on diet B which was significantly higher than those on diet C and D at week 4 and week 8, and the LPO value of the cats on diet D which was significantly higher than those of the cats on diet B and C at week 4. The vitamin E requirement of adult cats fed a high level of fish oil, using the response parameters measured, was estimated to be between 0 and 5 IU of vitamin E per g added fish oil per kg diet. The current recommendation of the Association of American Feed Control Officials (10 IU vitamin E/g fish oil/kg diet) appears to be well in excess. The results from the present study also showed that there was no beneficial effect of dietary vitamin E on whole blood cell proliferation when vitamin E levels were 150 % of the recommendations of the Association of American Feed Control Officials. The vitamin E requirement of adult cats to optimise immune response warrants further investigation.