1. Multi-drug residues and antimicrobial resistance patterns in waste milk from dairy farms in Central California
PN Tempini 1, SS Aly1,2, BM Karle3, RV Pereira1
1 Department of Population Health and Reproduction, School of Veterinary Medicine, UC Davis, Davis, CA.
2 Veterinary Medicine Teaching and Research Center, School of Veterinary Medicine, UC Davis, Tulare, CA.
3 Cooperative Extension, Division of Agriculture and Natural Resources, University of California, Orland,CA

2. Introduction Waste milk in dairy farms
Drug residues in Waste Milk
Tolerance of Drug Residues in Milk
Source : cdc.gov; en.wikipedia.org; enasco.com

3. Introduction Waste milk in dairy farms
Drug residues in Waste Milk
1 out of 3 Dairy Farms
(USDA, 2008)
$ savings per calf per day (Godden et al., 2005)
Health Hazards?
Source : allontario.ca ;

4. Introduction Feeding trial: Impacts of feeding milk with drug residues
No drug residues
Added drugs at
low concentrations
Impacts on Antimicrobial Resistance
β-lactams & Tetracycline
Cephalosporins
Multidrug Resistant
Source: Pereira RV et al. PloS one. 2014;9(12):e115223;

5. Objective
Identify and measure the concentration of antimicrobial residues in Waste milk (WM) samples on dairy farms in the Central Valley of California;
Survey farm management practices for factors that could suggest occurrence of specific antimicrobial residues in WM
Characterize the antimicrobial resistance patterns of E. coli cultured from WM samples.
Source : shutterstock.com; photosinbox.com

6. Drug Screening of Waste Milk
Material & Methods
Drug Screening of Waste Milk
Waste Milk Samples: 25 farms
Multi-Residues Screening & Quantification LC-MS/MS
On-Farm Questionnaire
Microbiological Testing
Source :; johnlund.com; farmbuildingguide.org; agilent.com

7. Results & Discussion Description Distribution (%)
Table. Distribution of drug residues in raw waste milk samples detected by liquid chromatography-tandem mass spectrometry(LC-MS/MS)
Description
Distribution (%)
LC-MS/MS test (n = 25)
Positive
Negative 15 10
Distribution by drug class
Only β-lactams
Only Sulfamethazine
Only Tetracyclines
β-Lactams and Tetracycline 1 3

8. Results & Discussion
Table. Drug residues in waste milk measured by LC-MS/MS and distributed by individual drug class.
Drug Residue
Number
Mean SE
Tolerance
(%)
(ng/mL)
β-Lactams:
11 (44)
Ceftiofur
7 (28)
251.14
177.0
100
Cephapirin
3 (12) 39
24.5 20
Penicillin G
1 (4) 10 -
Sulfonamides:
Sulfadimethoxine 7
Tetracyclines:
4 (16)
Tetracycline
590
300
Oxytetracycline
378.5
308.7

9. Results & Discussion Ceftiofur 13 22 19 10 17 Penicillin G 6 1 9 8 3
Table. Answers to “what are the two most common drugs used for/to treat”: dry cow treatment, mastitis, reproductive diseases, lameness and pneumonia (BRD).
Antimicrobial
Agent
Dry cow TX
Mastitis
Reproduct.
Diseases
Lameness
BRD
Ceftiofur 13 22 19 10 17
Penicillin G 6 1 9 8 3
Tetracycline
Cephapirin
Amoxicillin 7 2 4
Oxytetracycline 5
Sulfadimethoxine
Other Drugs
No Treatment

10. Non-fermentative gram Staphylococcus aureus
Results & Discussion
Table. Milk culture results for waste milk samples collected at dairy farms.
Bacteria
Positives (%)
(n = 25)
Streptococcus spp.
21 (84)
Staphylococcus spp.
20 (80)
Escherichia coli
10 (40)
Non-fermentative gram
negatives
8 (32)
Staphylococcus aureus
5 (20)
Bacillus spp.
Klebsiella spp.
4 (16)
Trueperella pyogenes
3 (12)
Mycoplasma spp.
2 (8)
Enterobacter spp.
1 (4)
Prothoteca spp.
Yeasts
Antimicrobial %
Resistant
β-Lactams
Ampicillin 30
Cephalothin 20
Ceftiofur 10
Tetracycline
Sulfonamides
Sulfisoxazole

11. Conclusion
LC-MS/MS revealed that ceftiofur was the most prevalent detectable drug residues, followed by cephapirin and tetracycline.
Multiple bacteria cultured were from waste milk, supporting the importance of pasteurization before feeding. Furthermore, the most common antimicrobials drug for which E. coli was resistant was ampicillin.
Most common drug used to treat sick cows on the farm was ceftiofur, followed by penicillin G and tetracycline. Ceftiofur was most the common drug used to treatment mastitis on farms (88%), followed by cephapirin (40%).

12. Questions / Comments Funding Sources:
U.S. Department of Agriculture Project number CA-V-PHR-4708-AH408