ORIGINAL CONTRIBUTION

Transfer of antibiotics between the udder quarters of dairy cows treated for clinical mastitis C A T H E R I N E LEONARD*, A C H U N T E R and D R F E N L O N Bacteriology Division, School of Agriculture, 581 King Street, Aberdeen

Milk samples from all quarters of I3 dairy cows, each treated with an antibiotic preparation for clinical mastitis in one quarter, were collected at each milking during treatment and for at least six milkings thereafter. After storage at -25"C, these were tested for the presence of antibiotics. Transfer to untreated quarters was found in eight of the 13 casesstudied, although in only two cases was the level in untreated quarters greater than 0.01 iu/ml. The main factor affecting transfer was found to be a history of infection in the treated quarter. This was observed in all but one case where transfer had occurred. During the period of study incorporation of milk from untreated quarters would not have raised the antibiotic level in the bulk supply to a level which would have incurred a financial penalty.

The presence of antibiotic residues in milk and milk products is undesirable to the consumer, and detrimental to the manufacture of cultured milk products (Smith, 1959). The Milk Marketing Boards in the United Kingdom have imposed stricter standards since January 1986 by reducing the acceptable level for inhibitory substances in milk from 0.02 iu/ml to 0.01 iu/ml. In order to prevent the entry of inhibitory substances into the bulk milk many farmers discard milk from treated quarters only. There is, however, some uncertainty as to whether the antibiotic diffuses from treated to untreated quarters (Blobel, 1960; Ziv & Gordin, 1974). Therefore it has been recommended that all milk from cows treated by intramammary antibiotic therapy be discarded. This study was devised to investigate the diffusion of antibiotics within the udder after intramammary infusion and determine the necessity to discard milk from untreated quarters in order to comply with the present Milk Marketing Board standards.

MATERIALS AND METHODS Thirteen cases of clinical mastitis involving 10 dairy cows were included in this investigation. Milk samples were taken from all quarters, treated and untreated, before every milking throughout the period of treatment and for at least six milkings thereafter. Samples were stored at -25°C and defrosted at room temperature immediately prior to testing. Antibiotic residues were tested by the disc assay plate method, used by Lyne & Lott (1984) in their modification of the method of Galesloot & Hassing (1962). The test organism was Bacillus stearothermophilus var calidolactis. Dilutions of milk from the treated quarter together with undiluted samples from the other three quarters were tested by dipping filter paper discs (Whatman 6 mm AA discs) in the milk, draining off the excess and placing on the surface of plate count agar plate (Oxoid, Basingstoke) seeded with the test organism. A standard curve ranging from 0 to 50 iu/ml was obtained using discs soaked in appropriate concentrations of penicillin. After incubation for 6 h at 55°C. the diameter of the clear zones around each disc were measured.

The antibiotic assay technique used was capable of detecting antibiotic concentrations of 0.0025 iu/ml. The extent to which transfer of antibiotics between quarters occurred is shown in Table I . The presence of antibiotic in untreated quarters was found in eight of the 13 cases tested, although in only two was

'Present addres5: Department of Epidemiology, New York State College of Veterinary Medicine. lthaca NY 14853.

the level higher than 0.01 iu/ml. Transfer was usually to all other quarters, but in cows 5 and 8 there appeared to be preferential transfer from front to rear quarters on the same side. Persistence of antibiotic was extremely variable, even in cows treated with the same antibiotic persistence ranged from 1-4 days.

Table 2 shows the relevant previous history of the cows sampled and includes lactation number, time elapsed since previous treatment, causal bacteria in quarters infected, somatic cell count and milk yield.

DISCUSSION There are a number of observations which can be made from the results of the limited number of cases studied. Antibiotics persisted for variable periods in the treated quarters, variation being observed between cows, between treatment of the same cow and between different antibiotics. Diffusion to other quarters did occur to varying degrees, but it seemed t o depend on the concentration achieved in the treated quarter. Hawkins, Cannon & Paar (1962) found that antibiotic transfer tended to be to the quarters on the same side of the udder. This was found in two of the cases reported here. However, in cow No. 8, the quarter to which the higher level of transfer occurred had a previous history of mastitis. The examination of herd records showed that in all but one case in which diffusion of antibiotic had occurred there had been previous treatment for mastitis in the same quarter in the current lactation. The interval between outbreaks was also significant, the shorter the interval the more likely was transfer to occur.

It was possible to calculate the probable concentration of antibiotic in the bulk tank after including milk from all quarters (including the treated one) or milk from untreated quarters only. Cows receiving treatment with Tetra delta, Leo1 Yellow and one cow receiving Orbenin were excreting antibiotic levels equivalent to 5 iu/ml in milk from the treated quarter. This milk would require a dilution in excess of 150 to be within the standard set by the Milk Marketing Boards, and it would still be detectable by the tests at dilutions in excess of 1:lOO. The variability of levels of excretion would make incorporation of any milk from treated quarters extremely irresponsible. It was, however, possible to include milk from untreated quarters without incurring a penalty, although in a herd with a high proportion of cows with a previous history of mastitis undergoing treatment there may be a risk. I t is

8 Journal of the Sociery of Dairy Technology, Vol. 41. No. I . February 1988

TABLE 1 Concentration and transfer between quarters of antibiotic used to treat udders affected with clinical mastitis

cow/ IMected Antibiotic Max conc (iu/m4 of No. of milkings Tranqfer to Max conc (iuJm4 sample quarter used antibiotic in milk to CO.01 iu/rnl other quarters in untreated quarters

l a Back L Orbenin 1.5 7 -ve lb Back R Orbenin 0.5 4 -ve Ic Back R Tetra delta 5.0 7 All 3 0.2 2a Back R Orbenin 0.023 4 All 3 co.01 2b Back R Orbenin 0.25 2 All 3 <0.01 3 Front R Orbenin 1 .o 6 -ve 4 Back L Orbenin 1.3 6 5 Front L Orbenin 5.0 6 Back L <0.01 6 Front R Leo1 Yellow 5.0 6 All 3 co.01 7 Back L Orbenin 3 .O 8 Front L co.01 8 Front R Orbenin 4.0 6 All 3 0.015 (back R) 9 Back R Orbenin 0.25 6 All 3 co.01 10 Front R Orbenin 1.3 6 -ve

TABLE 2 Herd rerord of cows treated for clinical mastitis

Present outbreak Previous outbreak Interval Somatic Milk No. Causal bacteria Infected quarter Causal bacteria Infected quarter between idectiom Cell Count Yield

(days) (OOOs/ml) (Nd) sample Lactation

la Ib l c 2a

2b

3 4 5

Str agalactiae Back L Str faecalis Back R Str agalactiae Back L Str faecalis Back R Str faecalis Back R E c&i Back R Str&sgalactiae Back R Staph aureus E coli E coli Back R Ecoli Back R Staph aureus Staph aureus Front R Str agalactiae Back L Staph aureus Front L Str uberis Front L

31 4 26

19

70

NA 23.6 330 18.0

1600 12.2 1500 18.9

NA 20.5

60 22.6 150 25.2

1 800 14.3 Staph aureus

Staph aureus

Str dysgalactiae

6 3 Staph aureus Front R Acinetobacter Front R 4 950 19.4

7 4 Staph aureus Back L Staph aureus Front L 1 1 260 20.6

8 3 Staph aureus Front R Staph aureus Front R & 17 4100 13.6 Back R

9 3 Staph aureus Back R Staph aureus Back R 10 1 Str agalactiae Front R

23 280 16.9 320 19.8

Staph aureus Str = Streptococcus; Staph = Staphylococcus; E = Escherichia; N A = not available

therefore important to keep up to date records of previous infections as these predispose transfer of antibiotics.

penicillin in milk from non-infused quarters following infusion of one quarter. Journal of Dairy Science 45 1020-1022.

Lyne A.R & Lott A F (1984) Inhibitory substances in animd feeds: experiences over the last five years. In Antimicrobiak in Agri- culture, pp 413-422. Woodbine M, ed. Proceedings of the 4th International Symposium on Antibiotics in Agriculture. Lmdon: Butterworths.

Smith v R (1959) Physiologv Of Lactation, 5th ed. London:

ziv Constable. and Gordin (1974) Mode of transfer of antibiotics from treated to non-treated quarters of dairy cows. American Journal of Veterinary Research 35 643-647.

REFERENCES Blobel H (1960) Concentration of penicillin. Journal of the American

Veterinary Medicine Association 137 110-1 13.

method for the detection of penicillin in milk. Netherlands Milk and Dairy Journal 16 89-95.

Hawkins G E, Cannon R Y & Paar G E (1962) Concentration of

Galeloot Th-E & Hassing F (1962) b.rapid and sensitive paper disc

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