Evaluating the antimicrobial use on dairy farms in Chiba Prefecture in Japan using the antimicrobial treatment incidence, an indicator based on Japanese defined daily doses from 2014-2016

Abstract

The use of antimicrobial agents in food-producing animals may lead to the emergence and spread of antimicrobial resistance in bacteria of animal origin. However, there is a paucity of data on the quantity of antimicrobials use on dairy farms in Japan. This study describes antimicrobial use on dairy farms from 1 January 2014 to 31 December 2016 in five administrative districts (central, eastern, western, southern and northern) of Chiba Prefecture. The use of antimicrobial agents in dairy cattle over these three years was evaluated in terms of the antimicrobial treatment incidence (ATI; theoretical number of animals per 1,000 animal-days subjected to antimicrobial treatment) using data collected from a total of 442 dairy farms in that prefecture. Our results revealed that the average ATI on these farms for these years ranged from 38.7 to 39.4 with no significant difference between years and that the average ATI for these administrative districts varied between 32.9 and 43.2 with a significant variation between some of the districts. Approximately 84% of antimicrobials were administered intramammarily, 13-14% by injection and 1-2% orally. Scenario analyses were performed to assess the effect of changes in some of the defined daily dose (DDDjp) values used to calculate the ATI. Our results revealed that the calculated ATI is considerably affected by the changes in the long-acting factor used for assigning the DDDjp values of intramammary products for dry cows and the way in which DDD values are assigned for combination products.

Keywords: antimicrobial treatment incidence (ATI); antimicrobial use; defined daily dose (DDD); dry cow therapy (DCT); mastitis.

Fig. 1.

Location of Chiba Prefecture and its five jurisdictional districts. Open circles indicate the location of NOSAI Chiba veterinary clinics. The numbers of farms in each district analyzed in this study are shown in parentheses. Blank map used for preparation of this figure was reprinted from https://www.freemap.jp/ under a CC BY license, with permission from Keisuke Inoue, original copyright 2006.

Fig. 2.

The average of antimicrobial use of the 442 farms in Chiba Prefecture in Japan in terms of the antimicrobial treatment incidencs (ATI) by antimicrobial class and administration route in 2014, 2015 and 2016. Intrauterine and oral route are categorized as others.

Fig. 3.

The antimicrobial treatment incidence (ATI) in 2014 to 2016 on dairy farms in different administrative districts (central, eastern, western, southern and northern) of Chiba Prefecture, based on the result of regression analysis using a linear mixed-effect model. The details of the results are shown in Supplementary Table 5. The error bars represent 95% confidence interval. Single, double and triple asterisk indicates a statistically significant difference with P<0.05, P<0.01 and P<0.001, respectively.

Fig. 4.

Relative distribution of antimicrobial use (a) and the average antimicrobial use in terms of the antimicrobial treatment incidence (ATI) (b) by antimicrobial class on 442 dairy farms in Chiba Prefecture, Japan in 2016, calculated using Japanese defined daily dose (DDDjp) values assigned assuming a long-acting factor of one, four, seven and ten days for intramammary products for dry cows. Macrolides, quinolones, sulfonamides, thiamphenicol and trimethoprim are categorized as others.

Fig. 5.

Relative distribution of antimicrobial use (a) and the average antimicrobial use in terms of the antimicrobial treatment incidence (ATI) (b) by antimicrobial class on 442 dairy farms in Chiba Prefecture, Japan in 2016, calculated using two different sets of Japanese defined daily dose (DDDjp) values assigned for constituent antimicrobial agents in combination products. Separate (baseline): DDDjp values assigned separately to each constituent antimicrobial agent of combination products as the weight of active ingredient of each antimicrobial administered per day per kg of animal; Single: single DDDjp values assigned to the combination products as the total weight of active ingredient of the two constituent antimicrobial agents administered per day per kg of animal. See Supplementary Table 3 for detailed way of calculation. Macrolides, quinolones, Sulfonamides, thiamphenicol and trimethoprim are categorized as others.