Abstract
A production experiment with blue and silver foxes was performed in order to reveal the long-term effects of feeding a diet abundant in polyunsaturated omega-3 fatty acids during the growth period. The main emphasis was on the growth performance and general fur characteristics of the animals. The experiment consisted of 200 blue foxes and 44 silver foxes and it lasted from July to pelting in 1988. The experimental diets were a SH = slaughterhouse offal based diet and a FM = fish mixture based diet supplemented with fish oil. The fat level of the diets was 20% in dry matter. In both fox species, there were no great differences between diets in the body weight of the animals at pelting. Only blue fox males in the FM dietary group were lighter than those in the SH group. In silver foxes, the dried raw skins were longer in the FM group than in the SH group. Fur characteristics were in general better in both blue and silver foxes on the FM diet than on the SH diet, except for the color purity of the fur skins, which was shown to deteriorate on the FM diet. Improved fur quality was, however, probably not due to the fish oil supplementation, but rather to the higher protein content of the FM diet. Animal losses on the FM diet (12) were higher than on the SH diet (1) in blue foxes. In the silver foxes studied, 2 animals died in the FM group. The deaths were likely caused by an excessively low feed temperature and, consequent to that, diarrhea, because the FM diet was mainly composed of frozen ingredients. Blue and silver foxes also differed from each other in feeding behaviour, which may have worsened the situation of the blue foxes. No clear differences could be shown in the animal growth performance of either blue or silver foxes. The deleterious or beneficial effects found in this experiment were probably not related to the accumulation of polyunsaturated omega-3 fatty acids in the animal's tissues and organs. The time period from July to pelting is likely to be too short to affect production performance.
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