🚧 Delvotest® T robust also for individual cow milk

Introduction

The use of antibiotics to treat cows is very important to control mastitis, one of the main diseases that affect the cows. On the other hand, the dairies and general public are becoming more aware of food safety issues and pushing for more control in the final products that they consume.

Being so, the trend in the dairy industry all over the world is to impose the Hazard Analysis Critical Control Point (HACCP) system to milk Production. Consequently, there is a need for an on-farm milk test for antimicrobials testing, so the farmer can ensure that the milk from individual cows can be delivered to the bulk tank. ¹ The use of a broad-spectrum test to detect the presence of residues of antibiotics in the milk used at individual cow, will prevent the farmer to contaminate the bulk tank with a milk that has antibiotics. ¹

Delvotest® T is a broad-spectrum microbial inhibition test with high sensitivity for Tetracyclines and a low rate of false positives that easily can be used to screen milk for antibiotic residues from individual cow milk. Results can be read visually and using systems able to evaluate the color change. DelvoScan® is such a system, based on standard flatbed scanner technology.

When we collect milk from an individual cow, a sample of the total composite milk is advisable because it is representative of the milk that will be added to the bulk tank. If a foremilk sample is collected, usually it contains a higher concentration of somatic cells than does a total composite milk ². 

Visually abnormal milk should not also be used as a sample to perform a microbial inhibition test. If the cow has a clinical mastitis, the Somatic Cell Count will increase, and other concentrations of other plasma components (i.e., bovine serum albumin and immunoglobulin) will be higher.  This and other components with antibacterial properties, such as lactoferrin, lysozyme, microbes, free fatty acids³ can inhibit the growth of the bacteria present in the test, Geobacillus stearothermophilus, leading to a false positive result.

The objective of this study is to evaluate the occurrence of false positive results from Delvotest® T when testing milk without antibiotics (from cows not treated with antibiotics or, when treated, sampled after the prescribed withdrawal time), and with a different range of components.

Materials and Methods

Among an Italian lactating Holstein Cow Farm having recurrent mastitis problems, 100 single cow samples of total composite milk were collected in July 2015. The samples were kept at ‹5 °C (no freezing) and tested after 24 hours with Delvotest® T for detection of antibiotic residues in a laboratory with ISO 17025 accreditation (*).

Test of samples using the Delvotest® T assay

Delvotest® T was prepared for the examination of the samples. The test was incubated in a water bath with a controlled temperature of 64 °C +/- 2 °C till the control time. The test was cooled down at 4 °C and read visually and with DelvoScan®.

Milk components

The Somatic Cell Count (cells x 10³ per milliliter), Fat (g/100 g, %), Protein (g/100 g, %), Lactose (g/100 g, %) and Total Bacterial Count (colony forming units x10³ per milliliter) were measured using a Foss System and it was done according to the manufacturer’s recommendations.

Results

Among the 100 samples tested 7 were coming from treated cows, with withdrawal time not yet expired. All 7 samples were found positive. Following data are referred to the remaining 93 samples.

Fat

The cows tested presented a range between 5.65 and 2.9 %, of fat in the milk, being the normal range for Holstein cows a value between 3.4 and 4 %. All milk samples tested did not presented a positive result towards the test, meaning that the milk without antibiotics did not present a false positive result in the presence of high or low values of fat.

Protein

The cows tested presented a range between 4.35 and 2.45 %, of protein in the milk, being the normal range of protein in Holstein cows between 3.2 and 3.6 %. All the milk samples tested did not present a positive result towards the test, meaning that the milk without antibiotics did not present a false positive result in the presence of high or low values of protein.

Lactose 

The cows tested presented a range between 5.47 and 4.41 %, of lactose in the milk, being the normal range of lactose between 4.0 and 5.0 % in Holstein cows. All the milk samples tested did not present a positive result towards the test, meaning that the milk without antibiotics did not present a false positive result in the presence of high or low values of lactose.

Somatic Cell Count 

The cows tested presented a range between 9223 x 10³ and 25 x 10³ SCC per milliliter in the milk. A healthy cow, with no sign of inflammatory disease will present results between 0 and 200 x 10³ SCC per milliliter of milk. According to the European Regulation (EC) No 853/2004 is not allowed to deliver milk from a farm if it contains more than 400 x 10³ SCC per milliliter. All the milk samples tested presented negative results even in presence of very high content of SCC, as 9 223 x 10³.

TBC  

The cows tested presented a range between 7962 x 10³ and 2 x10³ UFC per milliliter in the milk. A clean milk, without bacterial contamination, will present results between 0 and 50 x10³ UFC per milliliter. According to the European Regulation (EC) No 853/2004 is not allowed to deliver milk from a farm if it contains more than 100 x 10³   UFC per milliliter. All the milk samples tested presented negative results even in presence of very high content of bacteria in the milk, as 7 962 x 10³.

Lactating Days 

The cows tested presented a range between 2 days and 717 days after calving, which means that they would present different values also in their composition of chemical and physical characteristics of the milk. All the milk samples tested were negative. That confirms that there is no interference of the milk composition due to the days in lactation of the cows and the possible presence of false positives when testing using the Delvotest® T.

Table 1- Overview of the range of the components of the milk of the 93 negative single cow milk samples, regarding Fat, Protein, Lactose, SCC, and TBC. In figures, x-axis= Class of contents and y- Frequency

Conclusion

Delvotest® T can be used as one of the first screening procedures to avoid the contamination of the milk with antibiotic residues in the milk supply chain. Delvotest® T is a robust test that shows a good performance when used in milk samples from individual cow, even with different parameters of physic chemic properties, so of most value when used as a tool at the farm level in the implementation of the HACCP systems.

Document reviewed by Nicoletta Rizzi, Laboratory Manager, ARAL. Study performed in July 2015.

References

1. Kang, J.H. , Jin, J.H., and Kondo, F. 2005 - False Positive Outcome and Drug Residue in Milk Samples over Withdrawal Times. J. Dairy Sci. 88: 908-913
2. Andrew, S.M., Frobish, R.A., Paape, M.J., and Maturin,l.J. 1997 - Evaluation of selected Antibiotic Residue Screening Tests for Milk Individual Cows and Examination of Factors That Affect Probability of False Positive Outcomes.  J dairy Sci  80: 3050-3057
3. Carlsson, A. L. Bjorck, and K. Peterson. 1989 - Lactoferrin and Lysozyme in milk during acute mastitis and their inhibitory effect in Delvotest P® P. J. Dairy Sci. 72:3166

(*) ARAL, Accredia # 0518, PT Antibiotic residue detection