WO2005006849A1

WO2005006849A1 - Method and apparatus for indicating a health condition of a milking animal

Info

Publication number: WO2005006849A1
Application number: PCT/SE2004/001133
Authority: WO
Inventors: Mikael Gilbertsson; Mats Gustafsson
Original assignee: Delaval Holding Ab
Priority date: 2003-07-17
Filing date: 2004-07-14
Publication date: 2005-01-27
Also published as: SE0302094D0; SE0302094L; SE525789C2

Abstract

A method for indicating a health condition, e.g. incidence of mastitis, of a milking animal on-line during milking of the milking animal, comprises the steps of measuring the concentration of a specified ion, e.g. Na+, K+, H+, or Cl-, in the milk as drawn from an udder quarter or udder of the milking animal during the milking by means of an ion-selective sensor (40); comparing the concentration of the specified ion with a reference concentration value; and indicating a health condition, i.e. incidence of mastitis, of the milking animal depending on the outcome of the comparison.

Description

METHOD AND APPARATUS FOR INDICATING A HEALTH CONDITION OF A MILKING ANIMAL

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to dairy farming, and more specifically to methods and apparatuses for indicating a health condition, e.g. incidence of mastitis, of a milking animal on-line during milking of the milking animal.

DESCRIPTION OF RELATED ART AND BACKGROUND OF THE INVENTION

A major cause of loss in dairy farming is an infection, known as mastitis, which occurs in an animal's udder.. Mastitis is caused by contagious pathogens invading the udder and producing toxins that are harmful to the mammary glands. Generally, mastitis starts in one udder quarter.

Somatic cells, predominantly white cells and epithelial cells, enter the mammary gland as a result of damage to the alveolar lining by infection or chemical irritation. The counting of somatic cells excreted in the milk has become a widely used measure of mammary gland inflammation and mastitis. The somatic cells can be counted by laborious direct microscopic method on stained milk smears, or the cell numbers can also be estimated by direct chemical tests. Other methods measure milk somatic cells indirectly or by determining the concentration of various by-products of the inflammatory response.

One of these methods is based on measuring changes in the electrical conductivity of milk, as generally, ion concentration, and thus electrical conductivity, in mastitic milk is higher than in normal milk. Electrical conductivity is generally measured with a DC or AC circuit having a probe positioned in the flow of milk. The most sensitive part of this on-line method is the probe. The probe generally includes two electrodes to which an AC or DC current is supplied to create an electrical circuit through the milk. The conductivity of the milk is evaluated by measuring the current variations in the circuitry that includes the probe. However, the readings are often inaccurate due to deposits of colloidal materials from the milk on the electrodes, and also due to polarization. Polarization occurs because some of the ions migrating towards the electrodes are not neutralized and consequently, an offset, or leakage current is generated between the electrodes . The presence of the leakage current results in inaccurate conductivity readings. Different aspects on milk conductivity measurements have been patented, see e.g. U.S. Pat. Nos. 3,762,371; 5,416,417; 5,302,903; 6,307,362 Bl; and 6,378,455 Bl.

SUMMARY OF THE INVENTION

A general object of the present invention is thus to provide a method and an apparatus, respectively, for indicating a health condition, e.g. incidence of mastitis, of a milking animal on- line during milking of the milking animal, which lack the drawbacks and limitations associated with the prior art described above.

A particular object of the invention is to provide such a method and such an apparatus, which are automatic and capable of providing an indication of a health condition of a milking animal before the main part of the milking of that milking animal has been completed.

It is a further object of the invention to provide such a method and such an apparatus, which provide an indication of a health condition of a milking animal by analyzing the milk directly in the milking system used for milking that milking animal .

It is yet a further object of the invention to provide such a method and such an apparatus, which are capable of providing a separate health condition indication for each udder quarter of a milking animal.

It is still a further object of the invention to provide such a method and such an apparatus, which are reliable, flexible, of fairly low cost, and relatively easy to implement in existing milking systems.

These objects, among others, are according to the present invention attained by methods and apparatuses as specified in the appended patent claims.

The present invention is based on the use of an ion-selective sensor for measuring on-line during milking of a milking animal by a milking machine the concentration of a specified ion in the milk as drawn from the milking animal. The ion-selective sensor is connected to a computer provided with suitable software for post-processing of the data from the sensor. Preferably, an ion-selective sensor is provided in each milk line of the milking machine employed for the milking to measure the concentration of the specified ion in the milk on an udder quarter individual basis.

The present inventors have noted that such sensor provides for a measure, which is indicative of various health conditions of the milking animal. In fact, it has been verified in the laboratory that ions such as sodium, potassium and chloride are each extremely suitable as fast and sensitive indicators of various health conditions such as incidence of mastitis, a high somatic cell count (SCC) value in the milk, presence of blood in the milk, and a condition, at which the milk has a quality which is lower than a given quality.

The computer is provided with software for comparing the measured concentration of the specified ion with a reference concentration value ; and for indicating a health condition of the milking animal depending on the outcome of the comparison. The reference concentration value may be given as a value, which is considered to be normal for milk from a healthy milking animal in general, or normal for milk from the particular milking animal.

To obtain a fast probe, the ion-selective sensor or each one of the ion-selective sensors is preferably implemented in one or each one of the milk lines of the milking machine employed for the milking. Low carry-over effects have been noted experimentall .

A sensitive probe is obtained since the ion-selective sensor is capable of measuring very small concentrations of a specified ion. The specified ion shall be an ion, which has good correlation with the health condition to be indicated. The present inventors have noted that the sodium ion is an excellent candidate for indicating sub-clinic mastitis since the sodium ion concentration is fastly and heavily increased as soon as the milking animal becomes infected. Preliminary investigations show that the chloride ion would be a good indicator of clinic mastitis since the chloride ion concentration seems not to increase during the sub-clinic phase, but is strongly affected when the milking animal has developed clinic mastitis. According to a preferred embodiment of the present invention a particularly sensitive probe is obtained. Here, two different ion sensitive sensors are provided: one for measuring the sodium ion concentration and one for measuring the potassium ion concentration. Since it has been noted that the sodium ion concentration increases for a milking animal having mastitis, whereas the potassium ion concentration decreases, a very sensitive indicator can be obtained. Mastitis would be indicated only if the sodium ion concentration is above a first threshold and the potassium ion concentration is below a second threshold value.

Since mastitis may develop in a single udder quarter only, the sensitivity is further improved if an ion-selective sensor is provided in each milk line of the milking machine to measure the concentration of each ion in the milk for each udder quarter independently.

Ion-selective sensors such as ion-selective electrodes (ISE) and ion-selective field effect transistors (ISFET) are known in the art, see e.g. U.S. Pat. Nos. 4,844,097; 6,290,838 Bl and 6,297,871 Bl; the abstract of "Ion-selective field effect transistor (ISFET) -based calcium ion sensor with photocured polyurethane membrane suitable for ionised calcium determination in milk", A. Bratov et al., Anal. Chim. Acta, 408/1-2 (57-64), 2000; and the article "On-line microbial detection (part 1, microbial examination of milk)", N. Ashley, Dairy Industries International, Vol. 56, No. 10, p. 39(3), October 1991, the contents of which being hereby incorporated by reference. However, none of the documents describes ion-selective sensors as fast and sensitive probes for indicating a health condition of a milking animal, such as incidence of mastitis, or a high somatic cell count value in the milk from the milking animal on- line during milking. In fact, the latter article teaches away from the present invention by stating that "Impedance/ conductance generally will not be useful techniques for microbial determination in milk because of the need for growth of the micro-organisms in an overlong test time" .

Further characteristics of the invention and advantages thereof, will be evident from the following detailed description of preferred embodiments of the present invention given hereinafter and the accompanying Figs. 1-5, which are given by way of illustration only and thus, are not limitative of the present invention.

In the following detailed description the milk producing animals are cows. However, the invention is not limited to cows, but is applicable to any animals having the capability to produce milk, such as sheep, goats, buffaloes, horses, etc. By the term udder quarter is meant a separate milk production unit of a milking animal, where the milk produced therein is extracted through a single teat. Thus, provided that the animal is e.g. a sheep or a horse, the term udder quarter as used in the description should be exchanged for udder half.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates schematically, in a perspective view, main components of a milking machine provided with an apparatus for indicating a health condition, e.g. incidence of mastitis, of a cow on-line during milking according to a general embodiment of the present invention.

Fig. 2 illustrates schematically an ion-selective sensor for use in the apparatus for indicating a health condition of a cow. Fig. 3 is a plot of ion-selective sensor output voltage as measured by an inventive example apparatus for indicating incidence of mastitis of cows during milking on September 24 and 25, 2002.

Fig. 4 is a diagram of corresponding reference somatic cell count values as determined in the milk produced during the milking on September 24 and 25, 2002.

Fig. 5 is a diagram of the ion-selective sensor output voltage versus the logarithm of corresponding reference somatic cell count values, wherein the correlation coefficient between the quantities is indicated.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 illustrates some of the main components of an automated milking station for cows wherein the present invention is implemented. The automated milking station comprises four teat cups 11, of which only one is illustrated for sake of simplicity. Each teat cup 11 is connected to a respective milk tube 13, which in turn is connected to an end unit 15 via a respective valve or regulator 17, a respective milk conduit 18, a respective flow meter 19, and a common milk meter 21. The end unit 15 is connected to a vacuum source (not illustrated) via a milk/air separator 25 and a vacuum supply conduit 23.

During milking of the teats of a cow, the teat cups are attached to the teats of a cow typically by a robot arm (not illustrated) and vacuum is supplied to the end unit 15 via the vacuum supply conduit 23 to draw milk from the teats of the cow, through the milk lines 13 and into the end unit 15. The valves or regulators 17 may be used to control the individual vacuum levels in the teat cups 11. The milk from each udder quarter of the cow is measured individually by the flow meters 19; wherafter the weight of the milk from the cow is measured by the common milk meter 21. Finally, the milk is collected in the end unit 15 and the air is sucked out through the conduit 23.

Further, the milking machine comprises a pump and regulator system 27 for pumping the milk to e.g. a larger milk storage tank (not illustrated) via one 29 of a plurality of milk output lines 29, 31 connected to the end unit. Another milk output line 31 may be used for discarding milk from the milking of a cow, for pumping the milk to another tank, or for pumping the milk to a feed device for feeding calves.

The milking machine is advantageously connected to a computer- based processing and control device 35, which is responsible for processing and controlling of the milking machine, and comprises typically a microcomputer, suitable software, and a database including information of each of the cows milked by the milking machine, such as e.g. when the respective cow was milked last time, when she was fed last time, her milk production, her health, etc.

The present invention presents an improved apparatus for indicating a health condition of a cow on-line during milking. The apparatus, schematically shown by reference numeral 33 in Fig. 1, comprises one or several ion-selective sensors.

In Fig. 2 is schematically illustrated an example of such an ion-selective sensor in detail. This ion-selective sensor is an ISFET (ion-selective field effect transistor) 40 wherein two separated n-type regions of the semiconductor, the source S and the drain D, are implanted in a semiconducting p-type bulk silicon substrate B. A gate oxide 46 is deposited on top of the source and the drain. For the detection of other ions than protons, an ion-selective membrane 43 is deposited on top of the gate oxide 46 of the ISFET, creating a so-called MEMFET (membrane field effect transistor).

Optionally, an intermediate layer 44 consisting of polyHEMA (poly-2-hydroxyethyl methacrylate) is located between the ISFET gate oxide 46 and the ion-selective membrane 43. The polyHEMA is covalently attached to the ISFET gate oxide 46 by prior treatment of the surface thereof. The layer is soaked in a pH- buffer solution containing the specified ion to be measured. In this way the influence of the pH of the solution on the measurements is eliminated.

In the lateral dimension the ion-selective membrane 43 is surrounded by insulating resin 45. The ion-selective membrane 43 as well as a reference electrode 41 are exposed to milk 42 to be probed. If a positive external field VGS is applied to the surface of the ISFET, holes in the p-type bulk silicon are pushed away from the semi-conductor surface. If the potential is large enough electrons are attracted to the semiconductor surface, resulting in an inversion layer. When inversion sets in, a conducting channel 47 is formed by the electrons. Changes in VGS will result in changes in the density of electrons in the inversion layer. The change in the drain current through the inversion layer can be measured. In practice the drain current is kept constant by counteracting the change in the drain current by a change of the potential of the reference electrode 41.

The ion-selective membrane 43 is a very important part of the MEMFET because the receptor molecules, ionophores, in the membrane 43 determine the selectivity of the sensor for the ion to be measured over interfering ions. The ionophores form a strong complex with the target ion. The potential of the membrane depends on the ion concentration in the sample. A change in the membrane potential is converted into a change in current between the source and drain region of the field effect transistor. Because the signal is proportional to the logarithm of the concentration of the target ion a large range of concentrations can be measured.

The ion-selective sensor may be arranged in a separate conduit, provided for leading away a sample of the milk from one or several of the milk conduits 18. Optionally, the milk sample is brought back to the milk conduit(s) 18 or is brought to the end unit 15 after having passed the ion-selective sensor. Advantageously, however, the ion-selective sensor is arranged within one of the milk conduits 18.

Preferably, at least one ion-selective sensor is arranged in each one of the milk lines 18 to measure the concentration of at least one specified ion in milk from each one of the udder quarters of the cow independently. The reference electrode 41 may be common for a plurality of the sensors.

The following different ions in particular may be measured: α Na⁺ α K⁺ α CI^" α H⁺ (as pH value)

Furthermore, the temperature of the milk from each one of the udder quarters of the cow may be measured independently partly for calibration of the sensors, partly to be an indicator in itself or in combination with any of the ions listed above. Different ions may be probed in order to indicate different health conditions. The following health conditions may be indicated for each udder quarter independently by measuring one or several of the ions in the non-exhaustive list above: α incidence of sub-clinic mastitis α incidence of clinic mastitis α high SCC value in the milk α presence of blood in the milk α low quality of the milk (i.e. a quality lower than a given quality as defined in a selected one of a plurality of different manners)

The purpose of identifying cows and their udder quarters, which have a particular health condition, such as e.g. mastitis, increased somatic cell count (SCC) scores, or blood in the milk, may be to be capable of treat or monitor these cows, or to direct the milk from them to not mix it with milk from healthy cows or cows having low SCC scores.

Each of the ion-selective sensors 40 of the apparatus 33 is adapted to repeatedly sense the concentration of a specified ion (as a respective output voltage value) and is connected to provide the computer-based processing and control device 35 with a stream of output voltage data. The computer-based processing and control device 35 holds a reference value, which may be a value considered to be normal for milk from a healthy cow in general, or normal for milk from the particular cow or the particular udder quarter of the cow. The processing and control device 35 comprises software code for repeatedly comparing the output voltage data indicative of the concentration of the specified ion with the reference value; and for indicating a health condition of the udder quarter of the cow depending on the outcome of the comparison.

The indication may be any of the following: α A note in a field for that cow or that udder quarter of the cow in the database held by the processing and control device 35 α Alarm to a farmer of the health condition of the cow or the udder quarter of the cow in order for him/her to give the cow or the udder quarter of the cow a treatment α Indication to a device for automatically treat a cow to treat the cow α Indication to the milking machine to direct milk drawn from the udder or udder quarter of the cow to a specified one of a plurality of milk storage tanks α Indication to the milking machine to immediately interrupt the milking α Indication to a device for automatically clean the milking machine to clean the milking machine

It shall be appreciated that a selected one or more of the indications may be performed depending on the outcome of the comparison. For instance a slight discrepancy between a measured value and a reference value may give rise to a note in the database, whereas a larger discrepancy may give rise to an indication regarding treatment or milking.

It shall be further appreciated that two or more of the ions and optionally the temperature may be measured simultaneously, that each measured value may be compared with a respective reference value, and that the indication(s) to be made depend(s) on all or some of these comparisons.

Alternatively, an index value is formed from several measured values (where the different measured values may be given different weights), and is compared with a reference index value, wherein the indication(s) to be made depend(s) on that comparison. The present inventors have found that two different ion sensitive sensors for measuring the sodium ion concentration and the potassium ion concentration simultaneously would be a good option for indicating mastitis. Since it has been noted that the sodium ion concentration increases for a cow having mastitis, whereas the potassium ion concentration decreases, a very sensitive indicator is obtained. Mastitis would be indicated only if the sodium ion concentration is above a first threshold and the potassium ion concentration is below a second threshold value.

The operation of a sodium-selective sensor on-line during milking of the left rear udder quarter of a plurality of cows has been verified experimentally. The sensor employed was commercially available from SENTRON, The Netherlands.

Fig. 3 is an example of a plot of the voltage of the ion- selective sensor as readout every other second during milking of cows on September 24 and 25, 2002. The different cows milked are indicated by different numbers. Cow No. 929 developed clinic mastitis during September 24, 2002, and this can clearly be seen in the plot. The output voltage has dropped significantly (corresponding to a significant increase in the sodium ion concentration) at the second indicated milking around 11 pm on September 24, 2002 as compared with the first indicated milking around 6.30 pm on September 24, 2002.

Fig. 4 is a diagram of corresponding reference somatic cell count values as determined in the milk yielded during the milking on September 24 and 25, 2002. The somatic cell count values for cow No. 929 (the three bars correspond to the first, second and third milkings during the period) indicate that the sodium-selective sensor is faster than somatic cell counting for indicating mastitis. In order to determine whether the sodium-selective sensor is additionally a good indicator for indicating high somatic cell count values the output voltages from the sodium-selective sensor were correlated with the somatic cell count values. Fig. 5 is a diagram of the sodium-selective sensor output voltage versus the logarithm of the corresponding reference somatic cell count values. The correlation coefficient between the quantities was determined to be 0.4144.

During the experiments a slightly better correlation coefficient for the sodium-selective sensor as compared with a commonly used conductivity meter was obtained despite the fact that the signal from the sodium-selective sensor is a raw signal, which had not been statistically processed, filtered or correlated with other kind of data. It is believed that the correlation coefficient will be still higher if the sodium-selective sensor is combined with a potassium-sensitive sensor and/or a chloride-sensitive sensor.

The sodium ion is thus a suitable ion for indicating mastitis and also for indicating high SCC values since the sodium ion concentration in the milk from an udder quarter of a cow is increased as soon as the udder quarter of the cow becomes infected.

Preliminary investigations show that the chloride ion is a good indicator of clinic mastitis since the chloride ion concentration seems not to increase during the sub-clinic phase, but is heavily increased when the cow has developed clinic mastitis.

Furthermore, the temperature would be an indicator of an ill cow if it can be measured very accurately since the temperature of such a cow, and correspondingly of her milk, is typically increased.

It shall be appreciated that the present invention may include that indication(s) to be made depend(s) additionally on other data to obtain a yet more sensitive indicator. Such other data may come from any kind of knowledge of the cow, her udder quarters, or the milk from there. Measurement data may originate from devices measuring the behavior of the cow such as her activity, feed consumption, movement pattern etc. or from devices measuring the milk such as flow meters, conductivity meters, cell counters, etc. The reference and threshold values may additionally be established based on the above knowledge or data.

It shall be further appreciated that by implementing the embodiment described above in a milking machine with four end units (not illustrated) — one for each udder quarter, milk could be transported and taken care of on an udder quarter individual basis, e.g. milk from udder quarters having low SCC score may collected in one tank and milk from udder quarters having high SCC score may be collected in an other tank.

While the embodiments of the ion-selective sensors have been described as being mounted in the milk conduits 18, and thus measures concentration of a specified ion in milk from each single udder quarter independently, it may nevertheless be connected downstream of the point where milk from the udder quarters are mixed. For instance in a milking machine where the teat cups are connected to a single milk line via a claw (upstream of the end unit), the ion-selective sensor may be located in this single milk line. It shall still further be appreciated by the person skilled in the art that the present invention may be implemented in virtually any kind of automated, semi-automated, or manual milking system.

Further, the principles of the present invention may be implemented for another purpose to establish the quality of cleaning or rinsing of the milking machine, or as an indicator as to when cleaning or rinsing of the milking machine is ready.

According to one embodiment of the invention the milking machine is cleaned by a cleaning fluid, where the cleaning fluid has a concentration of a specified ion, which is distinct from the one, which the milk has. The concentration of the specified ion in the milking machine is monitored during the cleaning by means of an ion-selective sensor; the concentration of the specified ion as monitored during the cleaning is compared with a cleaning reference concentration value; and based on the comparison of the concentration of the specified ion as monitored during the cleaning and the cleaning reference concentration value, the cleaning is finished or the quality of the cleaning is indicated.

Similarly, the milking machine may be rinsed by a rinsing fluid before and/or after having been cleaned by the cleaning fluid, where the rinsing fluid has a concentration of the specified ion, which is distinct from the one, which the milk has and/or which the cleaning fluid has. The concentration of the specified ion in the milking machine is monitored during the rinsing by means of the ion-selective sensor; the concentration of the specified ion as monitored during rinsing is compared with a rinsing reference concentration value; and based on the comparison of the concentration of the specified ion as monitored during rinsing and the rinsing reference concentration value, the rinsing is finished or the quality of the rinsing is indicated.

Particularly, the H⁺ ion, i.e. the pH value, is monitored during the cleaning and/or rinsing.

If the milk, the cleaning liquid, and the rinsing liquid have similar concentrations of the specified ion, a given amount of the specified ion may be added to the cleaning liquid and/or the rinsing liquid. In this respect other ions than the ones having been exemplified in the present text may be employed.

Claims

1. A method for indicating a health condition of a milking animal on-line during milking of said milking animal by a milking machine, characterized by the steps of:

- measuring the concentration of a specified ion in the milk as drawn from an udder quarter or udder of said milking animal during said milking by means of an ion-selective sensor (40);

- comparing the measured concentration of said specified ion with a reference concentration value; and

- indicating a health condition of said milking animal depending on the outcome of said comparison.

2. The method of claim 1 wherein said specified ion is Na⁺.

3. The method of claim 1 wherein said specified ion is K⁺.

4. The method of claim 1 wherein said specified ion is CI^".

5. The method of claim 1 wherein said specified ion is H⁺, and the concentration of said specified ion is given as a pH value.

6. The method of any of claims 1-5 wherein said health condition includes incidence of mastitis .

7. The method of any of claims 1-6 wherein said health condition includes a high somatic cell count (SCC) value in the milk from the udder quarter or udder of said milking animal.

8. The method of any of claims 1-7 wherein said health condition includes presence of blood in the milk from the udder quarter or udder of said milking animal.

9. The method of any of claims 1-8 wherein said health condition includes a condition, at which the milk from the udder quarter or udder of said milking animal has a quality lower than a given quality.

10. The method of any of claims 1-9 wherein said milking animal is, in connection with said milking but subsequent to the step of indicating a health condition, automatically treated depending on the health condition indicated.

11. The method of any of claims 1-10 wherein a farmer is, in connection with said milking but subsequent to the step of indicating a health condition, automatically notified depending on the health condition indicated.

12. The method of any of claims 1-11 wherein milk drawn from the udder quarter or udder of said milking animal during said milking is, subsequent to the step of indicating a health condition, directed (29, 31) to a specific one of a plurality of milk storage tanks depending on the health condition indicated.

13. The method of any of claims 1-12 wherein the milking of said milking animal is, immediately subsequent to the step of indicating a health condition, interrupted depending on the health condition indicated.

14. The method of any of claims 1-13 wherein

- said milking machine is cleaned by a cleaning fluid, said cleaning fluid having a concentration of said specified ion, which concentration is distinct from the one, which said milk has; - the concentration of said specified ion is measured in said milking machine during said cleaning by means of said ion- selective sensor (40);

- the concentration of said specified ion as measured during said cleaning is compared with a cleaning reference concentration value; and

- a quality of said cleaning is indicated depending on the outcome of said comparison of said concentration of said specified ion as measured during said cleaning and said cleaning reference concentration value.

15. The method of any of claims 1-13 wherein

- said milking machine is rinsed by a rinsing fluid after having been cleaned by said cleaning fluid, said rinsing fluid having a concentration of said specified ion, which concentration is distinct from the one, which said cleaning fluid has;

- the concentration of said specified ion is measured in said milking machine during said rinsing by means of said ion- selective sensor (40);

- the concentration of said specified ion as measured during said rinsing is compared with a rinsing reference concentration value; and

- a quality of said rinsing is indicated depending on the outcome of said comparison of said concentration of said specified ion as measured during said rinsing and said rinsing reference concentration value.

16. The method of any of claims 1-15 wherein - the concentration of a second specified ion in the milk as drawn from the udder quarter or udder of said milking animal during said milking is measured by means of a second ion- selective sensor (40); and

- the measured concentration of said second specified ion is compared with a second reference concentration value, the health condition of said milking animal indicated being additionally dependent on the outcome of the comparison of said measured concentration of said second specified ion and said second reference concentration value.

17. The method of claim 16 wherein

- the concentration of a third specified ion in the milk as drawn from the udder quarter or udder of said milking animal during said milking is measured by means of a third ion- selective sensor (40); and

- the measured concentration of said third specified ion is compared with a third reference concentration value, the health condition of said milking animal indicated being additionally dependent on the outcome of the comparison of said measured concentration of said third specified ion and said third reference concentration value.

18. The method of claim 1 wherein

- said specified ion is Na⁺;

- the concentration of K⁺ in the milk as drawn from the udder quarter or udder of said milking animal during said milking is measured by means of a second ion-selective sensor (40);

- the measured concentration of K⁺ is compared with a second reference concentration value; and - a health condition of said milking animal, particularly incidence of mastitis, is indicated provided that the concentration of Na⁺ is above said first reference concentration value and the concentration of K⁺ is below said second reference concentration value.

19. The method of any of claims 1-18 wherein

- the temperature of the milk as drawn from the udder quarter or udder of said milking animal during said milking is measured by means of a temperature sensor; and

- the measured temperature is compared with a reference temperature value, the health condition of said milking animal indicated being additionally dependent on the outcome of the comparison of said measured temperature and said reference temperature value.

20. An apparatus including a processing means (35) and at least one ion-selective sensor (40) for performing the method as claimed in any of claims 1-19.

21. An apparatus for indicating a health condition of a milking animal on-line during milking of said milking animal by a milking machine, characterized in:

- an ion-selective sensor (40) for measuring the concentration of a specified ion in the milk as drawn from an udder quarter or udder of said milking animal during said milking; and a processing means (35) for comparing the measured concentration of said specified ion with a reference concentration value; and for indicating a health condition of said milking animal depending on the outcome of said comparison.

22. The apparatus of claim 21 further comprising a second ion-selective sensor (40) for measuring the concentration of a second specified ion in the milk as drawn from the udder quarter or udder of said milking animal during said milking, wherein

- said processing means (35) is adapted to compare the measured concentration of said second specified ion with a second reference concentration value, and to additionally base the indicated health condition of said milking animal on the outcome of the comparison of said measured concentration of said second specified ion and said second reference concentration value.

23. The apparatus of claim 22 wherein said first and second specified ions are Na⁺ and K⁺.

24. The apparatus of any of claims 21-23 wherein the indicated health condition of said milking animal includes any of incidence of mastitis; a high somatic cell count (SCC) value or presence of blood in the milk from the udder quarter or udder of said milking animal; or a condition, at which the milk from the udder quarter or udder of said milking animal has a quality lower than a given quality.

25. The apparatus of any of claims 21-24 wherein

- said ion-selective sensor (40) is adapted to measure the concentration of said specified ion in said milking machine during cleaning or rinsing said milking machine by a fluid, said fluid having a concentration of said specified ion, which concentration is distinct from the one, which said milk has; and said processing means (35) is adapted to compare the concentration of said specified ion as measured during said cleaning or rinsing with a cleaning or rinsing reference concentration value; and

- a quality of said cleaning or rinsing is indicated depending on the outcome of said comparison of said specified ion as measured during said cleaning or rinsing and said cleaning or rinsing reference concentration value.