Effects of formalin on bacterial growth in mink feed, feed consumption andreproductive performance of adult mink, and growth of mink kits

Feed that is typically used on commercial mink ranches is an ideal environm ent for bacterial growth because of the raw animal by-products used as ingr edients. Recently, formaldehyde was approved for use as an antimicrobial ag ent in poultry feed. Experiments in our laboratory were carried out to inve stigate the effects of incorporating different concentrations of formalin i nto the feed of mink on the growth of gram-negative and gram-positive bacte ria. Feed containing 0, 550 or 1100 ppm formalin was kept refrigerated for up to 7 d and the number of colony forming units of gram-negative and gram- positive bacteria derived from the feed was determined each day. Colony for ming units in the formalin-treated feed were significantly fewer than colon y forming units in untreated feed. In the second trial, feed containing the same concentrations of formalin was maintained at 30 C for 24 h and cultur ed bacterial colonies were counted at 0, 12 or 24 h of feed incubation. Bot h concentrations of formalin were effective in significantly reducing the n umber ai colony forming units. A feed consumption trial determined if mink [Mustela vison] preferred formalin-treated feed to non-treated feed kept re frigerated for up to 7 d. Consumption of feed treated with 1100 ppm formali n was significantly lower than consumption of the non-treated feed on d1, 2 , 4 and 5, but body weight was not affected. A long-term feeding trial dete rmined the effects of formalin on mink reproduction, early growth of offspr ing and quality of fur. Mink were fed formalin at concentrations of 0,:550 or 1100 ppm for approximately 140 d beginning 1 mo prior to mating until ki ts were weaned at 6 w of age. Mating success was not affected by consumptio n of formalin-treated diets, but kit survival at birth was adversely affect ed in mink consuming 1100 ppm formalin. Hemoglobin concentration, hematocri t, mean corpuscular volume, and mean corpuscular hemoglobin were significan tly decreased in 6-w-old kits, but there were no significant differences in any of these parameters between the kits exposed to 0 and 550 ppm formalin . In a second phase, some kits and their dams were continued on their respe ctive dietary treatments from weaning through pelting (approximately 220 an d 320 d, respectively). At pelting, hematocrits and hemoglobin concentratio ns for the kits fed 1100 ppm formalin were significantly less compared to t he control and 550 ppm formalin groups. There were no significant differenc es in body weights among female kits or adult female mink. The body weights of male kits in the 1100 ppm formalin group became significantly less than the body weights of male kitis in the control and 550 ppm formalin groups as the trial progressed. The quality of fur was highest for mink in the con trol group and lowest for mink in the 1100 ppm formalin group. While dietar y 1100 and 550 ppm formalin were effective in suppressing bacterial growth in the feed of mink, the deleterious effects of 1100 ppm formalin on kit su rvival, hematologic parameters, body weight, and quality of fur preclude fo rmalin use at this concentration.