Formic acid–sodium benzoate preserved slaughterhouse offal and supplementary folic acid in mink diet

Slaughterhouse offal from beef slaughtering was preserved with 16 g kg−1 formic acid and 3 g kg−1 sodium benzoate and used in mink feed throughout the production year. The ensiled offal replaced 0, 0.5 or 1.0 parts of the frozen stored slaughterhouse offal in the basal diet, the level of which was 300, 200 and 260 g kg−1 during growth-furring, breeding and lactation periods respectively. Because folic acid has a central role in formate metabolism and in all tissues of high rate of cellular division during the breeding and lactation periods, each diet group was further divided into two levels of supplemented dietary folic acid, 1.3 or 10 mg kg−1 DM. Weaning weights of male kits and lactating females, as well as early post-weaning growth and hemoglobin development were negatively affected by the highest silage level, providing 4.5 g formic acid kg−1 feed. The pelt quality of the groups that received silage was comparable to or even better (p < 0.10) than that of the group of untreated, frozen stored offal. Both male and female reproduction performance was good and unaffected by the dietary manipulations. The effect of increased dietary folic acid could not be seen in any of the reproduction parameters or in pre-weaning kit growth. Extensive formation of free fatty acids in the silage due to high ash content of the offal and probable subsequent fat saponification are suggested to be among the factors that led to the slightly impaired growth performance of the animals, especially before weaning. In conclusion, ensiling of slaughterhouse offal with formic acid and sodium benzoate is an applicable preservation method and inhibits microbiological spoilage for several weeks. The lower performance of animals during lactation and early postweaning periods indicates that the high level of use of silage containing formic acid should be limited to the period from approximately 12 weeks of age to pelting.