Mink urinary tract disease (MUTD) often presents as urolithiasis and/or cystitis and is known as an important cause of mortality in mink kits during the early growth season. Antimicrobial flock treatment has been routinely applied as preventive/therapeutic protocol on Danish mink farms with increased mortality associated with MUTD. The therapeutic effect of this treatment strategy has not previously been investigated. In this study, we applied controlled parallel group treatment trials to assess the effect of sulfadiazine/trimethoprim and amoxicillin treatment on mortality associated with MUTD in mink kits. On farm A, eight mink kits were diagnosed with MUTD post mortem in the treatment group (n = 1920, sulfadiazine/trimethoprim treatment: 30 mg/kg, q 24 h, P.O for 5 days) compared to 16 in the untreated control group (n = 1920). No significant difference in mortality associated with MUTD were found between the treatment and the control group using the Fisher's exact test (P = 0.15). Treatment group 2 (n = 1920, amoxicillin treatment: 14 mg/kg q 24 h, P.O for 5 days) and treatment group 3 (n = 2088, amoxicillin treatment: 7.5 mg/kg q 24 h, P.O for 5 days) were investigated on farm B. Eight and four mink kits were diagnosed with MUTD post mortem in group 2 and 3, respectively. No difference between occurrence of MUTD were found between the control group and treatment group 2 (P = 0.42) or treatment group 3 (P = 0.75). No significant difference between final body weights or weight gain were found between treatment and control weighing groups on farm A or B. In conclusion, antimicrobial treatment administered in the feed showed no significant effect on weight gain or mortality associated with MUTD on the farms included in this study.
Keywords: Antibiotics; Cystitis; Treatment; Urolithiasis; Veterinary
Mink urinary tract disease (MUTD) presents as urolithiasis and/or cystitis diagnosed post mortem in mink kits [[
Use of antimicrobial flock treatment to target cystitis [[
Controlled parallel group treatment trials were performed on two Danish mink farms in Jutland during July–September 2018 (farm A) and July–August 2020 (farm B). The clinical trial protocol was approved by the Danish Medical Agency. Kits 2 months of age were included. Mink kits housed on farm A were of fur colour types brown and white and 1920 (n) of each type were included. Animals on farm B were of colour type brown and a total of 5976 was included. Mink kits were housed in traditional sheds with standard cages meeting the requirements of Danish law (one female and male kit in each). Animals were fed a standard mixed feed supplied daily from one local commercial feed kitchen. Farm A used a daily feed additive of ammonium chloride (2–3‰) from end of treatment to trial termination.
The farmers contacted their farm veterinarian because MUTD spontaneously occurred in early July. The farms met the inclusion criteria of the study specified in Table 1. During necropsy (at trial inclusion) bladder swabs (n = 4 from each farm) were collected from mink with lesions compatible with MUTD without visual signs of decomposition. The swaps were submitted to routine culture analysis and antimicrobial susceptibility test.
Table 1 Farm mortalities, sampling and necropsy results of MUTD (mink urinary tract disease) during study enrolment
Average kit mortality before recognition of clinical featuresa of MUTD Average kit mortality after recognition of clinical featuresa of MUTD Fraction of necropsied kits with MUTDb Datesc ‰ per day Datesc ‰ per day Farm A 27/6–29/6 2018 0.3 3/7–5/7 2018 0.6 11d/12 Farm B 23/6–27/6 2020 0.3 1/7–5/7 2020 0.7 10d/12
Study inclusion criteria: 100% increased kit mortality caused by MUTD (minimum 2/3 of necropsied mink kits diagnosed post mortem with MUTD)
Animals were randomly selected for trial groups by row (farm A) or house (farm B). Animal data is presented in Table 2. From each group 42 animals were randomly selected for weighing groups. Weight of the same animal was recorded at initiation and 12 weeks later and weight gain calculated. On farm A, treatment group 1 (n = 1920) were administered one daily dose of 30 mg/kg sulfadiazine/trimethoprim for 5 days. At farm B, treatment group 2 (n = 1920) were administrated a daily dose of 14 mg/kg amoxicillin for 5 days and treatment group 3 (n = 2088) received a daily dose of 7.5 mg/kg amoxicillin for 5 days. Treatment was administered in feed by adding a daily prepared stock solution to the water supply of the feeding machine at one daily feeding. Preparation and administration of the stock solution were supervised by the research group. The protocol included instruction for handling of kits with clinical signs of MUTD (the normal farm practice), but no cases were observed.
Table 2 Displaying trail groups at farm A and B including enrolled animals, treatment and weight groups
Farm A Farm B Antimicrobial agent Sulfadiazine 200 mg/g + trimethoprim 40 mg/g (Trimazin Forte Vet.) Amoxicillin 697 mg (Octacillin Vet.) Trail duration 7th of July to 1st of October 2018 9th of July to 1st of September 2020 Treatment specifications Sulfadiazine/trimethoprim: 30 mg/kg q 24 h, P.O for 5 days Amoxicillin: 14 mg/kg q 24 h, P.O for 5 days Mink kits (n) 1920 1920 Color type (n) Brown (n = 960); White (n = 960) Brown (n = 1920) Weight group 42 (n) males (21 brown, 21 white) 42 (n) females (21 brown, 21 white) 42 (n) brown males 42 (n) brown females Treatment specifications Amoxicillin: 7.5 mg/kg q 24 h, P.O for 5 days Mink kits (n) 2088 Color type (n) Brown (n = 2088) Weight groups 42 (n) brown males 42 (n) brown females Treatment specifications Administered pure water in the same amount as the treatment group Administered pure water in the same amount as the treatment group Mink kits (n) 1920 1968 Color type (n) Brown (n = 960); White (n = 960) Brown (n = 1968) Weight groups 42 (n) males (21 brown, 21 white) 42 (n) females (21 brown, 21 white) 42 (n) brown males 42 (n) brown females
Throughout the study period all dead mink kits were collected and stored on − 20 °C until examination. Using previously described procedures [[
Results of post mortem examinations and statistical analysis of this data are presented in Tables 3 and 4. MUTD was less prevalent in the treatment group 1 (8/1920) compared to the control group (16/1920). There was a significant difference between starting weights of males on farm A. Likewise, there were a significant difference between starting weights of females in group 3 and the control group at farm B. Results of microbiological culture are presented in Table 5. Staphylococci were detected in 70% of mink kits with lesions in farm A and 44% in farm B. Isolates identified as S. delphini group A made up 83% of the staphylococci isolated. Antibiotic susceptibility test showed no resistance of cultured staphylococci to sulfadiazine trimethoprim at farm A or amoxicillin at farm B.
Table 3 Results of post mortem examination, animal body weights and statistical testing from farm A
Farm A Treatment group 1 Control group P-value Dead kits with urinary tract diseasea (n) 8 16 Remaining mink kitsb (n) 1912 1904 0.15c Mortal urinary tract disease prevalence 4.2‰ 8.3‰ Mean (± SD) Start weight females (g) 905 (± 115) 915 (± 107) 0.68d Start weight males (g) 1224 (± 127) 1137 (± 143) 0.004d Final weight females (g) 1951 (± 221) 2010 (± 260) 0.27d Final weight males (g) 3571 (± 353) 3505 (± 371) 0.41d Weight gain females (g) 1046 (± 227) 1095 (± 239) 0.34d Weight gain males (g) 2349 (± 350) 2364 (± 307) 0.84d
Table 4 Results of post mortem examination, animal body weights and statistical testing from farm B
Farm B Treatment group 2 (T2) Treatment group 3 (T3) Control group (C) P-value T2 vs. C T3 vs. C T2 vs. T3 Dead kits with urinary tract diseasea (n) 8 4 5 Remaining mink kitsb (n) 1912 2084 1963 0.42c 0.75c 0.25c Mortal urinary tract disease prevalence 4.2‰ 1.9‰ 2.5‰ Mean (± SD) Start weight females (g) 1144 (± 97) 1126 (± 135) 1188 (± 129) 0.10d 0.02d 0.52d Start weight males (g) 1520 (± 256) 1509 (± 202) 1522 (± 224) 0.97d 0.80 d 0.83d Final weight females (g) 1288 (± 201) 1225 (± 260) 1258 (± 207) 0.81d 0.12d 0.18d Final weight males (g) 4206 (± 430) 4140 (± 470) 4130 (± 538) 0.48d 0.92d 0.54d Weight gain females (g) 1521 (± 235) 1436 (± 343) 1538 (± 268) 0.54d 0.52d 0.21d Weight gain males (g) 2676 (± 320) 2631 (± 393) 2608 (± 462) 0.44d 0.79d 0.61d
Table 5 Microbial findings of mink bladder specimens sampled post mortem from farm A (n = 23) and B (n = 16)
Microbial culture findings of bladder specimensa Farm A Farm B 15b 4b 3c 2b 3c 2b 1b 2b 2b 1b 1b Sterile (n) 2c 5c
No significant difference was found between mortality associated with MUTD in the treatment and the control groups, by means of the Fisher's exact test at a 5% significance level (results presented in Table 4). MUTD associated mortality is mainly seen in male mink kits [[
The antimicrobial flock treatment initiated after diagnosis of MUTD did not significantly reduce mortality associated with MUTD during the growth period. As illustrated in Figs. 1 and 2, mortality associated with MUTD occurred throughout the investigation period with no obvious culmination of disease. This result may have been affected by the relatively low post mortem prevalence of MUTD in the groups (1.9–8.3‰). Both farms presented with mortality associated with MUTD (0.6 and 0.7‰/day) at the time of inclusion. As a rule of thumb, kit mortality after weaning should not exceed 1‰ per week (0.14‰/day).
Graph: Fig. 1 Cumulative number of mink diagnosed with mink urinary tract disease (MUTD) at post mortem according to date. Farm A
Graph: Fig. 2 Cumulative number of mink diagnosed with mink urinary tract disease (MUTD) at post mortem according to date. Farm B
Both urolithiasis (56% and 65%) and infection with staphylococci (44% and 70%) were frequent findings. This is in agreement with previous studies investigating MUTD [[
One recent study reported mink of colour type black being predisposed to MUTD compared to brown mink [[
Sulfadiazine/trimethoprim and amoxicillin are first choice therapy for uncomplicated urinary tract infections in dogs and cats [[
Weight gain in mink kits can be considered an indicator for health and thriftiness. In this study, there were no significant differences between groups when comparing final weights or average weight gain. Thus indicating, that the applied treatment did not affect general health and growth.
Isolates submitted for antimicrobial susceptibility testing were susceptible to the applied antimicrobial drugs, however, only few isolates were tested (n = 4 from each farm). We cannot rule out, that antimicrobial resistance may have contributed to the lack of treatment effect. Bacterial isolates from Danish mink have shown ampicillin resistance in up to 82.3% of E. coli isolates [[
Prevalence of MUTD diagnosed post mortem ranged between 1.9 and 8.3‰ in study groups, which is consistent with previously reported mortality prevalences of MUTD on Danish mink farms [[
In conclusion, antimicrobial treatment had no significant effect on weight gain or mortality associated with MUTD in this study. While flock treatment of farms with MUTD is currently commonly applied, our results do not support this practice. More research is needed to ensure prudent and efficient use of antimicrobials and especially the use of flock treatment, which accounts for most of the antibiotics used for production animals. The results emphasize the need for improved and documented protocols for the prevention of MUTD.
We are grateful to the breeders involved in the project for their participation, for their indispensable help implementing treatments and weighing groups as well as for donating animal carcasses. In addition, we thank veterinarian Sanne Tygesen Skønager for assisting KM during trail implementation in 2018.
KM executed trail treatments and sampled all data. KM analyzed data and discussed results with ASH and PEP. ASH and PEP helped KM design the study and guided through the whole trail. KM wrote the article. All authors participated and contributed to interpretation and discussion of the results. All authors read and approved the final manuscript.
This study was co-funded by the Innovation Fund Denmark [grant number 7038-00033B and The Research Foundation of the Danish Fur Breeders Association. None of the funding sources were involved in design, collection of samples, analyses, interpretation or writing of the manuscript.
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
No ethical or laboratory animal permission was required as only spontaneous disease outbreaks were studied and as no experimental infection of animals took place. The animals were handled according to national legislation.
Not applicable.
The authors declare that they have no competing interests.
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By Karin Mundbjerg; Peder Elbek Pedersen and Anne Sofie Hammer
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