GB1592152A - Apparatus for the detection of mastitis in cows - Google Patents

Description

(54) APPARATUS FOR THE DETECTION OF MASTITIS IN COWS (71) We, MADATA LIMITED, of 171 Telegraph Road, Heswall, Wirral, Merseyside, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to apparatus for the detection of mastitis in cows and in particular for identifying which quarters of the udder are infected. The aim, in practice, is to detect the disease early enough to prevent a crosswise infection between the quarters of the udder of the cow concerned and also crosswise infection of the rest of the herd, and contamination of the milk so as to render it unfit for consumption.

A cows udder has four quarters which are entirely separate from one another and almost invariably mastitis appears in one quarter first, so that only the milk from the corresponding teat is infected and the infection can then spread progressively to the remaining quarters. When milk is infected by mastitis various changes occur in the characteristics of the milk which can be detected by a clinical analysis of a sample of infected milk to confirm the presence of mastitis. However, the clinical analysis is not often available or convenient and various attempts have been made to utilize the variation in one or other of the character istics of the milk to identify the presence of mastitis.

One of the main characteristics of mastitis infected milk is that the lactose content decreases, which effects the osmotic pressure in the udder, which must always remain the same as the blood-pressure of the cow. In order to counteract this decrease in the lactose there is an increase in sodium chloride which maintains the osmotic pressure at the correct level. Due to the increase in the sodium chloride content of the milk, the conductivity increases, and the more advanced the infection, the more the lactose will decrease and therefore the more the sodium chloride content will increase thereby increasing the conductivity of the milk.

Accordingly, several attempts have been made to detect mastitis utilizing this increase in conductivity, but various problems arise if one attempts to select a "norm" for a healthy cow with which to compare any measurements taken. The conductivity of the milk from a particular cow can in fact vary daily, and even hourly, dependent upon various factors and as such it is virtually impossible to select a suitable norm. However, it has long been known that for a particular cow the various factors effect each quarter of the udder equally, so that in the absence of mastitis the conductivity of the milk from the various quarters will rise and fall in parallel.

In a previous apparatus for the detection of mastitis, the milk is passed through a chamber containing a pair of electrodes during milking and the current which flows between the two electrodes is determined by the conductivity of the milk in the chamber. This current may be measured to provide an indication of the conductivity of the milk. In this case each teat must be checked individually and the likelihood of infection of any of the teats is then determined by comparison of the conductivity of each of the samples with the lowest conductivity measured, this being the most likely to be uninfected. As an alternative to this the electrodes may be incorporated into a bridge circuit so that when the conductivity, and hence the resistance of the milk alters the bridge is put out of balance, and a reading is produced.The bridge may contain further pairs of electrodes in some or all of the remaining arms of the bridge so that a plurality of samples of milk, each from a different teat may be checked simultaneously.

With two chambers forming part of the bridge, two teats may be measured and compared at a time but it is still necessary for at least three sets of measurement to be taken to determine whether mastitis is present and in which teat.

With an apparatus having measuring chambers connected in all four arms of the bridge, it is possible to provide a comparative result from all four teats of the udder, but with such an arrangement it is also possible that if two teats corresponding to adjacent arms of the bridge are infected then the bridge may not give an out-ofbalance indication. Therefore, a cow having mastitis in two teats may not always be detected, and therefore such an arrangement would not be reliable unless the measuring chambers are changed around to different teats as a check.

It is therefore the aim of the present invention to seek to provide an apparatus for detecting mastitis which provides a reliable indication of the presence of the infection without the necessity of checking the results.

According to the present invention there is provided an apparatus for detecting mastitis in cows, comprising four individual collecting chambers each for receiving a static sample comprising a predetermined minimum amount of milk to be tested, said collecting chambers each including a pair of electrodes connected in a detector circuit, said detector circuit being constructed and arranged so as to provide an output when the conductivity of one, two or three of the samples differs by more than a predetermined amount from the lowest conductivity detected.

The detector circuit may comprise a bridge having four parallel arms each containing a standard resistor, a pair of electrodes and a diode, the arms being connected in two pairs with the standard resistor and the pair of electrodes being connected in series between the supply rails, and the diodes being connected at the common point of said resistor and said pair of electrodes. The diodes of each pair being mutually connected to the input or the output of a detector/amplifier. In the first pair of arms the diodes are connected to the input of said detector/amplifier at their cathodes, and in the second pair of arms the diodes are connected to the output of the detector/amplifier at their anodes.With this arrangement of bridge, when the conductivity of one or more of the samples is increased relative to one or more of the remaining samples, the bridge is in an unbalanced condition and the current flows through the amplifier/detector, the output of which can be used to actuate an indicator.

The percentage variation of the conductivity can be set by means of a potentiometer.

An alternative arrangement of the circuit comprises a bridge having four arms, one of the arms including one pair of electrodes, a second arm including three pairs of electrodes connected in series, a third arm balancing the second arm having a standard resistor and the fourth arm of the bridge including a second standard resistor one third the size of the first standard resistor.

With this arrangement an excess conductivity in one or more of the samples being measured would unbalance the bridge and provide an output which could be used to actuate an indicator device.

In another arrangement a conventional bridge circuit may be used having one pair of electrodes in each arm and in which the four arms are electronically or electromechanically switchable to enable the different possible combinations of arms to be compared.

In each of the above arrangements a reliable indication of the presence or absence of mastitis can be obtained, but since it is desired to determine which of the teats are infected, then additional quantitative measurements of the conductivity must be made taking the lowest measured conductivity as the norm for that particular animal, and comparing the conductivity of the remaining quarters of the udder to determine which are infected.

In a fourth arrangement, the detector circuit comprises an electronic switching circuit having four parallel pairs of electrodes connected thereto, whereby the switching circuit determines between which pair of electrodes the lowest conductivity sample is situated, and then successively compares each of the remaining samples with the previously detected lowest conductivity sample. A level detector connected to the output of the electronic switching circuit determines whether any of the samples exceed the lowest conductivity sample by more than a predetermined amount and an indicator is actuated. Once the presence of mastitis has been determined the four pair of electrodes are connected into a measuring circuit containing a conductivity meter so that the infected teat or teats can be identified.

It has been found, in preliminary tests carried out under the supervision of the Veterinary Investigation Centre, the results of which were analysed by the Ministry of Agriculture Research Laboratories, that a mastitis detection unit according to the present invention correctly identified 97.5 % of the uninfected samples tested, and that it had correctly identified 95% of the infected samples tested. In fact, the unit had correctly identified the condition of 100% of the cows tested but the percentages were reduced to 97.5% and 95% when identifying the individual teats. The results were obtained by comparing the conclusions taken from the measurements made on the unit with the finding of laboratory tests carried on the same samples.

Preferably, the unit is constructed as a portable unit for testing selected animals so that the conductivity of the milk can be conveniently tested daily, and the onset of mastitis can be identified at an early stage, i.e. at sub-clinical level. Thus, the diease could then be treated before it develops to a stage where the milk becomes unfit for consumption, thereby significantly reducing losses due to mastitis.

The present invention will now - be described further by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a first measuring chamber; Fig. 2 shows a second type of measuring chamber; Fig. 3 shows a conventional Wheatstone bridge circuit; Fig. 4 shows a first bridge circuit of the present invention Fig. 5 shows a second bridge circuit of the present invention Fig. 6 shows an automatic electronic detector circuit and Fig. 7 shows a circuit for measuring conductivity of individual samples.

In Figures 1 and 2, two alternative types of measuring chambers 1 are shown. In the chamber of Figure 1 electrodes 2 and 3 are provided at the base of the chamber 1, the first electrode 2 being in the form of a rod and the second electrode 3 being in the form of an annular disc surrounding the first electrode 2 and insulated therefrom by an insulator 4. In this type of chamber it is important that the minimum level indicated by the line 5 should always be achieved so as to ensure the uniformity of measurements, although, once the level 5 is attained, the addition of extra milk does not significantly alter the conductivity of milk between the electrodes 2 and 3.

In the chamber of Figure 2 the electrodes 2 and 3 are provided on opposite walls of the chamber 1 and insulated from one another. The appropriate minimum level of milk is attained by incorporating a selflevelling tube 6 in the chamber 1 the upper end of which tube 6 is at or above the minimum level and all that is required to enable a measurement to be taken is to ensure that the milk level is at least level with the upper end of the tube 6. Any excess milk will, in fact, flow over into the tube 6 and may be collected if required.

With regard to the material of the chambers it is important that the chambers should be fairly easy to sterilize and may be made of sterilizable plastic such as polypropylene, epoxy resin or malemine, or ceramic materials and the electrodes' made of graphite or stainless steel or any other material which is resistant to chemical attack. For the measurement of the con ductivity of the milk from each teat of a cow it will be necessary to provide four chambers, which may either be completely separate from one another, or be separate portions of a single dish or the like.

In the circuit of Figure 3 a conventional Wheatstone bridge arrangement is shown in which a variation of the conductivity of any one of the arms, A, B, C or D would result in unbalancing the bridge and producing a current in the detector G which would be proportional to the change in the conduc tivity. However, with such arrangement, presuming all the arms are initially equal, if two adjacent arms were to alter simul taneously and the remaining two arms were unaltered, then the bridge would still be in balance, and no change would be detected.

Therefore, if such an arrangement were used for detecting mastitis, then there would be a strong possibility that a fair proportion of the measurements taken would be incorrect if two of the teats were equally infected. To avoid this problem all that is necessary is to provide an electromechanical or electronic switching means which enables all possible combinations of arms to be compared, i.e.

AB to CD, AC to BD, and AD to BC which ensures that even when two adjacent teats are infected, a reliable indication of the presence of mastitis will be given.

In Figure 4 a bridge circuit is shown having four parallel arms each containing a standard resistor R, a pair of electrodes 2 and 3, and a diode D. The arms are con nected in two pairs with the standard resistor R and the electrodes 2 and 3 of each arm being connected in series between the supply rails. The diodes D of each arm are con nected at the common point of the resistor R and the electrodes 2, and each pair are mutually connected to the input or the out put of a detector/amplifier A. In the first pair of arms, the diodes D are connected to the input of said detector/amplifier A at their cathodes and in the second pair of arms the diodes are connected to the output of the detector/amplifier A at their anodes.

With such an arrangement, whenever the conductivity of one or more of the samples is increased relative to one or more of the remaining samples, the bridge is in an un balanced condition and current flows through the amplifier/detector. The output of the amplifier/detector can be supplied to an indicator, and the percentage variation in the conductivity can be set by means of a potentiometer, so that an indication of the presence of mastitis will be given when the output from the amplifier exceeds a pre determined level.

In the arrangement of Figure 5 another type of bridge circuit is shown which will enable the change of the conductivity of one or more of the samples to be reliably indicated. This bridge has four arms arranged as in a conventional bridge, but one of the arms includes only one pair of electrodes 2 and 3, and the second arm includes three pairs of electrodes 2 and 3 connected in series, a third arm balancing the second arm has a standard resistor Y, and the fourth arm of the bridge includes a second standard resistor Y/3 which has a resistance which is one third of the size of the first standard resistor Y. With this arrangement an excess conductivity in any one of the samples being measured would unbalance the bridge and provide an output which could actuate an indicator device when a predetermined threshold is exceeded.

In the previous two arrangements it is necessary, once mastitis has been detected, to measure the conductivity of each of the samples and make a visual comparison of their conductivities taking the lowest conductivity as the norm for the particular cow being checked and determining which of the samples have a conductivity exceeding the previously selected norm by sufficient amount to indicate mastitis.

In the circuit of Figure 6, a substantially all electronic mastitis detection system is shown, utilising an electronic switching circuit 22 having pairs of electrodes from each measuring chamber 11, 12, 13, 14 as parallel inputs thereto. The switching circuit 22 is driven by an oscillator 20 via a buffer and oscillator amplitude stabilizer 21 and is controlled by a sequence oscillator 23. The electronic switching circuit 22 measures the conductivity of each sample and holds and compares the conductivities of all of the samples with one another to determine the lowest conductivity. The switching circuit then takes the lowest conductivity as its norm and compares each of the remaining samples with the norm.The result of this comparison is supplied to a detector amplifier 24 and then to a level detector 25, and if any of the samples exceeds the norm by a predetermined amount set on the level detector 25, then a fail indicator 27, which may be a red light, is actuated. If none of the samples exceeds the norm by the amount set on the level detector 25 then a pass indicator 26 is actuated, which may be a green light.

Once the comparison has been carried out and a fail indication has been given, it is necessary to measure the conductivities individually and determine which of these is the lowest, and then to make a further comparison- to determine which of the teats may be infected. Of course, it is possible, by utilising more sophisticated electronic means, to provide for automatic identification of the infected teat or teats following the comparison in the switching circuit 22 and simultaneous with the actuation of the fail indicator. However, such modifications would necessarily increase the cost of the device, and may, in fact, be preferable to simply provide for the pass or fail indication to be provided as a quick check later, more detailed, measurements being taken when convenient.

A simple circuit for enabling the conductivity of the individual samples to be measured is shown in Figure 7 and this may in fact be incorporated in the same instrument as the circuit of Figure 6 and therefore utilize common components to minimize cost. In this arrangement an AC voltage is applied across each sample in turn and applied to a conductivity meter via a full wave rectifier 29. The conductivity of each sample is noted and the lowest conductivity is identified and then a straight comparison is then made between the remaining conductivities and the lowest conductivity to determine the infected teat or teats.

The circuits of Figures 6 and 7 may be incorporated into a portable unit which may be used, by a farmer, with the minimum of technical knowledge and without supervision, or could form a very useful piece of apparatus for a Veterinary Surgeon. In each of the above arrangements an AC supply is used to avoid the polarisation effect inherent with a direct current source, which may cause electrolytic action in the milk. Whilst it is possible to obtain results with a wide range of frequencies, it has been found that a marked improvement in the accuracy of the measurements and the reliability of the identification of mastitis is obtained if a stabilised frequency in the approximate range of 1KHz to 15KHz is used, and particularly 3.2KHz.It is also important that the wave shape should be symmetrical, with the forward and reverse currents being equal in amplitude and period, since if the symmetry is not equal, then polarization will take place and cause lower conductivity readings. The voltage supplied to each sample should not exceed six volts since this may cause changes in the constitution of the milk sample which may adversely effect the readings.

WHAT WE CLAIM IS:- 1. An apparatus for the detection of mastitis in cows, comprising four individual collecting chambers, each for receiving a static sample comprising a predetermined minimum amount of milk to be tested, said collecting chambers each including a pair, of electrodes connected in a detector circuit which detector circuit is constructed and arranged so as to provide an óutput when the conductivity of 1; 2 or 3 of the samples

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (19)

**WARNING** start of CLMS field may overlap end of DESC **. type of bridge circuit is shown which will enable the change of the conductivity of one or more of the samples to be reliably indicated. This bridge has four arms arranged as in a conventional bridge, but one of the arms includes only one pair of electrodes 2 and 3, and the second arm includes three pairs of electrodes 2 and 3 connected in series, a third arm balancing the second arm has a standard resistor Y, and the fourth arm of the bridge includes a second standard resistor Y/3 which has a resistance which is one third of the size of the first standard resistor Y. With this arrangement an excess conductivity in any one of the samples being measured would unbalance the bridge and provide an output which could actuate an indicator device when a predetermined threshold is exceeded. In the previous two arrangements it is necessary, once mastitis has been detected, to measure the conductivity of each of the samples and make a visual comparison of their conductivities taking the lowest conductivity as the norm for the particular cow being checked and determining which of the samples have a conductivity exceeding the previously selected norm by sufficient amount to indicate mastitis. In the circuit of Figure 6, a substantially all electronic mastitis detection system is shown, utilising an electronic switching circuit 22 having pairs of electrodes from each measuring chamber 11, 12, 13, 14 as parallel inputs thereto. The switching circuit 22 is driven by an oscillator 20 via a buffer and oscillator amplitude stabilizer 21 and is controlled by a sequence oscillator 23. The electronic switching circuit 22 measures the conductivity of each sample and holds and compares the conductivities of all of the samples with one another to determine the lowest conductivity. The switching circuit then takes the lowest conductivity as its norm and compares each of the remaining samples with the norm.The result of this comparison is supplied to a detector amplifier 24 and then to a level detector 25, and if any of the samples exceeds the norm by a predetermined amount set on the level detector 25, then a fail indicator 27, which may be a red light, is actuated. If none of the samples exceeds the norm by the amount set on the level detector 25 then a pass indicator 26 is actuated, which may be a green light. Once the comparison has been carried out and a fail indication has been given, it is necessary to measure the conductivities individually and determine which of these is the lowest, and then to make a further comparison- to determine which of the teats may be infected. Of course, it is possible, by utilising more sophisticated electronic means, to provide for automatic identification of the infected teat or teats following the comparison in the switching circuit 22 and simultaneous with the actuation of the fail indicator. However, such modifications would necessarily increase the cost of the device, and may, in fact, be preferable to simply provide for the pass or fail indication to be provided as a quick check later, more detailed, measurements being taken when convenient. A simple circuit for enabling the conductivity of the individual samples to be measured is shown in Figure 7 and this may in fact be incorporated in the same instrument as the circuit of Figure 6 and therefore utilize common components to minimize cost. In this arrangement an AC voltage is applied across each sample in turn and applied to a conductivity meter via a full wave rectifier 29. The conductivity of each sample is noted and the lowest conductivity is identified and then a straight comparison is then made between the remaining conductivities and the lowest conductivity to determine the infected teat or teats. The circuits of Figures 6 and 7 may be incorporated into a portable unit which may be used, by a farmer, with the minimum of technical knowledge and without supervision, or could form a very useful piece of apparatus for a Veterinary Surgeon. In each of the above arrangements an AC supply is used to avoid the polarisation effect inherent with a direct current source, which may cause electrolytic action in the milk. Whilst it is possible to obtain results with a wide range of frequencies, it has been found that a marked improvement in the accuracy of the measurements and the reliability of the identification of mastitis is obtained if a stabilised frequency in the approximate range of 1KHz to 15KHz is used, and particularly 3.2KHz.It is also important that the wave shape should be symmetrical, with the forward and reverse currents being equal in amplitude and period, since if the symmetry is not equal, then polarization will take place and cause lower conductivity readings. The voltage supplied to each sample should not exceed six volts since this may cause changes in the constitution of the milk sample which may adversely effect the readings. WHAT WE CLAIM IS:-

1. An apparatus for the detection of mastitis in cows, comprising four individual collecting chambers, each for receiving a static sample comprising a predetermined minimum amount of milk to be tested, said collecting chambers each including a pair, of electrodes connected in a detector circuit which detector circuit is constructed and arranged so as to provide an óutput when the conductivity of 1; 2 or 3 of the samples

differs by more than a predetermined amount from the lowest conductivity detected.

2. An apparatus as claimed in claim 1, in which the circuit is a, bridge circuit having four parallel arms each containing a standard resistor, a pair of electrodes and a diode, the arms being connected in two pairs with the standard resistor and the pair of electrodes being connected in series between supply rails, each of the diodes being connected at the common point of the respective resistor and pair of electrodes, the diodes of each pair being connected to the input or output of a detector.

3. An apparatus as claimed in claim 1, in which said circuit is a Wheatstone bridge circuit, each arm of which includes a pair of said electrodes, and electromechanical or electronic switching means are provided for enabling said arms to be switched so that opposite and adjacent pairs of arms can be compared with the remaining two arms in each case.

4. An apparatus as claimed in claim 1, in which the circuit is a bridge circuit having four arms, in which one arm contains three pairs of electrodes in series, a second arm contains one pair of electrodes, a third arm balancing the first arm contains a standard resistor, and a fourth arm contains a standard resistor having a resistance one third the size of first standard resistor.

5. An apparatus as claimed in claim 1, wherein the circuit comprises an electronic switching circuit with the pairs of electrodes connected as parallel inputs to the switching circuit, the circuit including means for measuring the conductivity of a milk sample between each pair of electrodes, means for storing the conductivities measured, means for determining and selecting the lowest conductivity of those measured, and means for comparing the remaining conductivity with the selected conductivity and providing an output proportional to any differences detected.

6. An apparatus as claimed in any preceding claim wherein a level detector is provided connected to the output of said circuit, which detector, when said output exceeds a predetermined level, provides an output to actuate a visual or audible indicator.

7. An apparatus as claimed in claim 6, wherein separate indicators are provided for outputs below and above said predetermined level to provide a clear indication of the absence or presence of mastitis.

8. An apparatus as claimed in any preceding claim wherein the supply for said circuit is an AC supply.

9. An apparatus as claimed in claim 8, wherein said AC supply is in the frequency range of 1 kHz to 15 kHz.

10. An apparatus as claimed in claim 8 or 9 wherein the AC supply has a stabilised frequency of 3.2 kHz.

11. An apparatus as claimed in claim 8, 9 and 10, wherein the wave form of the supply is of uniform frequency and amplitude and the positive and negative halves of the signal are equal.

12. An apparatus as claimed in any preceding claim, wherein the output of said circuit is applied to a measurement circuit including means for accurately indicating the conductivity of each sample measured.

13. An apparatus as claimed in claim 12, wherein the measuring circuit measures each sample individually and switch means are provided for each sample to be connected in turn into the measuring circuit.

14. An apparatus as claimed in claim 12 or 13 when dependent on claim 5, wherein the electronic switching circuit and the measurement circuit utilize a common AC supply.

15. An apparatus as claimed in claim 12, wherein separate measurement circuits are provided for each sample so that they can be displayed simultaneously.

16. Apparatus as claimed in claim 5, wherein the electronic switching circuit includes means for indicating which sample or samples differs from the lowest conductivity measured by more than said predetermined amount.

17. Apparatus as claimed in any preceding claim wherein the electrodes are located in the base of the collecting chamber and take the form of a centre electrode and an annular electrode spaced apart and insulated from one another by means of an insulator member.

18. Apparatus as claimed in any of claims 1 to 17, wherein the electrodes are mounted on the sides of the collecting chamber and a levelling device in the form of an overflow tube is provided extending through the base of the cylinder and extending at least up to the minimum milk level.

19. An apparatus for the detection of mastitis in cows, substantially as hereinbefore described with reference to and as illustrated in any of Figs. 4, 5, 6 or Fig. 6 in combination with Fig. 7, or the accompanying drawings.