Patent Publication Number: US-2022217950-A1

Title: Ruminant animal monitoring system

Description:
The present invention relates to a system for automatically monitoring a ruminant animal, in particular a dairy animal such as a cow, comprising a 3D camera system for obtaining a plurality of 3D images of at least a region of interest of the animal at consecutive points in time during at least a predetermined period of time, a control device connected to the 3D camera system, the control device being provided with an image processing device for processing the obtained plurality of 3D images, and an output device. 
     Such animal monitoring systems are known. E.g. document WO12/138290A1 discloses a system for determining a gut fill level of the rumen of a dairy animal. A 3D camera system determines the depth or the volume of the rumen triangle. Also known are 3D camera-based body condition scoring systems. 
     However, a gut fill level or body condition score is only of limited importance for the health status of a ruminant animal. 
     Also known is WO9901026A1, that discloses e.g. a movement sensor and/or a breathing sensor, that comprises either a tactile sensor (pair) or a non-contact sensor such as a laser distance sensor or ultrasound sensor, or a camera with image processing. 
     However, no details are given about what image processing may lead to reliable breathing rate determination, and although this document discloses a method of determining breathing rate, in practice it turns out to not always provide reliable values. 
     Thus, there is a need for a practical, simple and reliable system and method for determining more and/or better health indication information about a ruminant animal, such as based on 3D images of the animal. 
     The present invention achieves this goal at least partly, and in one aspect provides a system for automatically monitoring a ruminant animal, in particular a dairy animal such as a cow, comprising a 3D camera system for obtaining a plurality of 3D images of at least a region of interest of the animal at consecutive points in time during at least a predetermined period of time, a control device connected to the 3D camera system, the control device being provided with an image processing device for processing the obtained plurality of 3D images, and an output device, the control device being arranged to determine a health parameter frequency value of a health parameter on the basis of the processed images, and to output the health frequency parameter value to the output device, wherein the image processing device is arranged to determine a region of interest in the plurality of 3D images and one of calculate for each 3D image a curvature value of the region of interest, and determine the calculated curvature as a function of time, or measure for each 3D image a relative position of at least one predetermined point of said region of interest with respect to the animal, and determine said relative position as a function of time, wherein the control device is arranged to determine points in time when local extreme values of the function of time occur, and the health parameter frequency value by analysing said points in time. 
     Use herein is made of the insight that looking at health related movements per se to determine a health parameter (or indicator) value may suffer from noise from e.g. other, voluntary animal movements. Determining the frequency of those health related movements is then even more difficult in the prior art. In the present invention, use is made of determining a curvature value, which is more specific in that it relates to the shape of the body (part). Even if the animal as a whole moves, the shape of the body part is less likely to change and thereby affect the determination of the health parameter frequency value. Thus, the present invention at least provides an alternative system to determine the health frequency parameter value(s), and may also serve to improve existing prior art systems for determining such value. 
     The monitoring in the present invention relates to determining a frequency value of a health related parameter (movement). Important health information is based on such bodily movements, and in particular their frequency. Examples thereof will be elucidated further below. Moreover, it is important or at least advantageous, to determine said health information in a non-contact fashion, because contacting the animal may itself cause stress and changes in the animal, which may lead to misdetermination of the health indicator. In addition, having a non-contact sensor allows to determine the health indicator in many different animals, without a need for e.g. a wearable sensor device on the animal. 
     Herein, the analysing of the points in time where the local extreme values occur may be as simple as determining the average time period between consecutive local extreme values, and then taking the inverse, for frequency. In fact, for the purpose of the present invention, frequency and its inverse, the characteristic time period, are taken to be equivalents. Moreover, more precise or alternative methods may also be employed, as will be elucidated later. 
     In the method, the local extreme values of the function may be determined as, in particular, local maxima in time, of the calculated curvature value or the relative position. A maximum in position is here taken to be a position closest to the 3D camera. “Local” is considered in the mathematical sense of “with respect to the variable”, not necessarily with respect to position in space. 
     The images are obtained at consecutive points in time. These points in time need not be distributed at regular intervals in time, but they need to be known in order to allow a temporal analysis of the images. Furthermore, the images should also be obtained during at least a predetermined period of time, again in order to allow a reasonable temporal analysis. The timeframe depends on the expected recurrence intervals, that may depend on the type of movement/health indicator, the type of animal etc. In practice, it is preferred for many types of movements if the images are obtained during at least 2 minutes, and more preferably during at least 5 minutes, although longer periods are of course not excluded. At least for cows, this allows to observe a sufficient number of movements or contractions for a reliable determination of a health indicator. 
     Other special and inventive embodiments are described in the dependent claims, as well as in the now following part of the description. 
     The 3D camera may be immobile or may be moveable, as long as it is arranged to observe at least one region of interest. Thereto, it could be provided with a lens with such a field of view that the region(s) of interest will be comprised in the image for all likely positions of the animal with respect to the 3D camera, taking into account that the animal may move during obtention of the images. In particular, the 3D camera may be arranged to be directable to the, or a, region of interest, by means of a provided mover control, connected to the control device. The control device may then be able to actively direct the 3D camera to the desired region(s) of interest, for example based on the image processing. It is then possible to use a smaller field-of-view, which in turn allows a higher accuracy. It also allows the system to determine more than one health parameter frequency, by accordingly arranging the control device and/or the mover control to direct the 3D camera to view the regions of interest that correspond to the desired health parameters. 
     Determining a region of interest in the plurality of 3D images may advantageously benefit from some form of tracking, especially when the animal moves. For example, the image processing device is arranged to recognise a particular point in the image, and use that point to track and position the consecutive images for comparison. Based on such tracking, a camera&#39;s mover control may be arranged to position the 3D camera such that the recognised point is always in the same position in the image. 
     In embodiments, the 3D camera system comprises a time-of-flight camera or a structured-light camera. Such types of 3D camera provide a relatively high framerate of upto 30 Hz or more. This ensures that contractions or other movements of the region of interest will not be missed between images, while animal movements may easily be accounted for in the obtained 3D images. However, it is not necessary to have such high frame rates, which lead to a relatively high number of calculations. Other 3D camera types, such as stereo cameras, or laser scanners are also possible. Examples of preferred 3D camera are the MESA Imaging “SwissRanger” 3D cameras or equivalents, and “Kinect” type camera devices. In all this, the property of the camera to provide 3D information is put to use in the invention to provide curvature data of the animal&#39;s region of interest. 
     In embodiments the curvature value comprises or is an average value of the curvature value of the region of interest, in particular averaged over a plurality of points across the region of interest. The curvature value may be determined according to any desired method, as long as it is an indication of the degree of curvedness of the surface. This value may, according to this embodiment, be determined by analysing the complete or partial region of interest. It is also possible to analyse a plurality of points in said complete or partial region, again as long as a good indication of the degree of curvedness is obtained. In addition, it is noted that the sign of the curvature value should not be ignored, in that a convex region of interest should give a positive value and a concave region of interest a negative value, or vice versa, as long as the two are different. This prevents meaningless double peaks if the region of interest should vary in appearance between convex and concave. 
     A useful example of calculating curvature of the surface (region of interest) is by Principal Component Analysis of a covariance matrix with neighbours for points on the surface. This gives three eigenvalues λ 0 , λ 1 , λ 2  for the matrix, and the curvature σ for a point may be estimated by σ=λ 0 /(λ 0 +λ 1 +λ 2 ), with λ 0  is the smallest eigenvalue. The surface curvature may then be determined by averaging (or adding, etc.) the surface curvature for a number of points, such as a matrix of points, in the region of interest. It turns out that a grid or lattice of surface points around some fixed and easily recognisable point in the region of interest suffices, as already stated above. The fixed point could e.g. be the surface point used for tracking, with the highest cross-correlation coefficient. Yet this is not to exclude other ways of estimating surface curvature, such as by calculating the variation of all the surface normal vectors in the region of interest, or the part/window thereof. 
     After determining the surface curvature, which can be done for each image, the result is a curvature that is a function of time. In analysing this function, local extremes, in particular local maxima, are determined. Herein, it is advantageous to consider a value a local extreme if it is the highest in a window of a predetermined time before and after that value&#39;s time, such as a few seconds, say 3 s. This prevents noise spikes etc. from interfering too much. 
     In embodiments, the control device is arranged to compare the determined health parameter frequency value with a predetermined frequency criterion. The extremes, in particular the maxima, will occur with some more or less regular frequency. By determining this frequency, or frequency band, valuable information about the health of the animal may be obtained, and a health indication given. 
     In embodiments, the control device is arranged to filter the function in time of the calculated curvature by filtering out temporal variations in said function that have a frequency outside a predetermined frequency range. With this measure, irrelevant changes, such as those caused by animal movements/displacements or noise, may effectively be removed. Herein, use is made of the insight that the relevant health related movements or contractions occur within an animal specific frequency band. In particular, but non-limiting embodiments, the control device is arranged to perform a Fourier transformation of the calculated curvature function to construct a transformed frequency function, then to remove all parts of the transformed frequency function outside the predetermined frequency range to obtain a clean frequency function, and determine a contraction frequency by analysing the clean frequency function. Fourier transforms are a well-known and effective way of removing frequency components from a temporal signal. Yet, other ways of filtering may be applied, such as bandpass filters, that achieve a similar effect. The analysing of the clean frequency function may be done by determining the frequency value with the strongest signal value, or the average of the frequency signals within the remaining signals in the clean frequency function, or any other analysis that gives a frequency value indicative of the contraction frequency. In addition, but only optionally, the control device may be arranged to perform an inverse Fourier transformation on the clean frequency function, to obtain a clean curvature function. This clean curvature function may be displayed for visual checking. 
     In embodiments, said frequency criterion comprises generating a health warning when the determined health parameter frequency value is lower than a predetermined lower frequency threshold or higher than a predetermined higher frequency threshold. It is found that for normal animals, the frequency with which health related movements or contractions occur has a certain value or lies in a certain bandwidth, and also that for animals suffering from clinical or even subclinical diseases, this frequency changes. This allows to determine a health warning, such as an entry on an attention list, a message to a farmer or veterinarian, an audible or visible alarm, etc. All this serves to draw attention to a specific animal for further health checks, because it was found that some value was out of the ordinary for said animal. 
     In embodiments, said lower frequency threshold, said higher frequency threshold, respectively, is a historical value for said animal, in particular a historical average for said animal, or is a literature value for said animal, in particular in dependence of one or more of a breed, an age, a number of days in lactation or gestation, or a type of activity or feed or feeding scheme, of said animal. This allows to finetune the frequency threshold(s) to animal specifics, in order to prevent unnecessary health warnings. It is remarked here that literature values may be a starting point, while processing historical values, optionally by means of deep learning and so on, may lead to threshold values with improved reliability. Examples will be given below. 
     In embodiments, said frequency threshold is dependent on a type of activity being performed by the animal, such as feeding, being milked, or resting. Herein, use is made of the insight that the frequency of the health related movements depends on the type of activity that the animal is momentarily involved in. For example, if the animal is eating, the frequency will often be higher, i.e. on the high side within the expected frequency band. Contrarily, in stress situations, or when resting, the frequency may be lower, such as for reticuloruminal contractions, or higher, such as for breathing. Thus, by determining these values, or two or more other health parameter frequency values, more reliable information may be obtained, and unnecessary health warnings may be prevented. 
     In embodiments, the system comprises at least one station, each station selected from the group of milking stations, feeding stations, drinking stations, treatment stations, separating stations, calving pens and selection stations, wherein the 3D camera system comprises a 3D camera provided in at least one of said stations. Such stations are well-suited for placing the 3D camera system, for the animal will be in one position for a relatively long time. In particular a milking station is well suited, because it may even be predicted for how long the animal will remain there, based on expected milk yield and other historical data. On average, the animal will be present in the milking station for at least 5 minutes, which provides a very suitable time window for determining the frequency as already stated above. But also at other stations such measurements with the 3D camera system are possible. Even when not every instance leads to reliable measurements, for example because the animal stays in a suitable position for a too short time, the system of the invention allows to monitor the animal at many instances, so that a good insight in its health may be obtained, and a warning can be given early in case something is wrong. It is remarked here that at each station, besides the measuring of health related movements or contractions, some other action may be performed, such as milking, feeding, treating or separating the animal. Advantageously, a separating station is coupled to a milking station or feeding station, such that in case a health warning is given for a particular animal in the station, the control device may send the animal to the separating station for it to await a health check by the farmer or veterinarian. 
     In embodiments, the control device is arranged to determine time intervals between the local extremes based on the determined points in time, and to analyse the points in time by comparing the determined time intervals with a predetermined time interval criterion. In the above, the system uses a frequency based analysis to determine a health indication or warning. Yet, it is also possible to base the analysis on the time intervals between the local extreme values. In fact, this analysis would come down to the same as frequency based analysis after a transform from the time domain to the frequency domain. Yet, in some cases it may be simpler to just analyse the various time intervals, such as by determining an average time interval between local maxima. Such average time interval should then be within a time interval range, that may be animal dependent, activity dependent and so on. All features relating to special embodiments in the frequency dependent analysis system also apply for the time interval based analysis system. 
     An important health parameter frequency is the breathing rate, and the region of interest is at least a part of a rib cage of the animal. Thus, in embodiments the control device is arranged to direct the 3D camera to the rib cage of the animal. 
     In particular, the higher frequency threshold is from 45-75 per minute, inclusive. These values hold for cows in particular, wherein the threshold value for a cow is preferably taken to be about 45)/minute, and for a calf between about 50 and 75/minute. Of course, other values may also be used, in particular for other types of animals. These values may be taken from literature. 
     Another important health parameter frequency is rumen motility, and the region of interest is a left paralumbar fossa, in particular a partial region within said left paralumbar fossa. Knowledge of the reticuloruminal motility may provide valuable health information. The reticulorumen performs digestive functions a.o. by cyclically contracting and relaxing. Herein, primary contractions start from the reticulum and pass across the rumen. These contractions mix and circulate the digesta. These contractions may be observed by means of the 3D camera. Note herein that determining only a single value of the curvature in time, such as might be derivable from the prior art systems that determine a depth or volume of the rumen area, or a body condition score, from a single image, would not lead to any information regarding contractions. 
     It is noted that rumen motility is sometimes determined by a veterinarian, by auscultation (listening to bodily sounds) and palpitating (examining by feeling the body). This requires the presence of a veterinarian, which is impractical for continuous monitoring. Thus, in practice it is only used if there is a suspicion of some health problem anyway. Thus, the chance of determining health problems or a precursor thereto, at a very early stage, is hereby excluded. In addition, practical tests have shown that human observation of the contractions in a well-filled rumen is more difficult than can be achieved with the system according to the present invention, which thus gives advantages in terms of reliability. Veterinarian&#39;s motility determination can also lead to errors and subjectivity, because of human assessment. But it also leads to stress or other disturbance for the animal or herd. This in itself may be a cause for deviations in the true reticuloruminal motility, so that the veterinarian might be led to an incorrect assessment due to stress or the like that is caused by his own assessing. For these reasons, the invention provides a non-contact system for determining a health indication. 
     In above embodiments, the region of interest is a left paralumbar fossa, also called the rumen triangle. This is the more or less triangular region on the left side of the ruminant animal, that provides a relatively clear view of the reticulorumen. It is easily recognisable automatically, e.g. by means of template matching, using a triangle, and matching regions of relatively high local curvature. A comparable method is described in https://nl.mathworks.com/help/images/ref/normxcorr2.html and reference is made to this source for mathematical details. In particular the region of interest is a partial region within said left paralumbar fossa, i.e. not the whole rumen triangle but only a smaller or larger part of it. It was found that the useful information may also be collected by looking at a part of the paralumbar fossa, which limits the number of determinations and calculations. 
     In embodiments, the higher frequency threshold is about 4 per minute, and/or wherein the lower frequency threshold is about 0.5 per minute. For example, when animals are fed mainly roughage, the contraction frequency is generally higher than when animals are fed a concentrates rich diet the threshold may then be adapted accordingly. 
     Alternatively or additionally, the health parameter is labour contractions, and the region of interest is the abdomen of the animal. The bulging of the abdomen is an indication of labour contractions. The frequency of the contractions, in particular the increasing thereof, is an indication of the stage of calving (in cows) etcetera. 
     For example, the higher frequency threshold is from 5-10/hour. Labour contractions in cows often start around 12-20/hour, and increase to about 40/hour. The health warning may be based on the determined frequency, and may depend on e.g. how near a farmer or veterinarian is. Of course, other values are possible, such as for other types of animals. 
     In a second aspect, the present invention relates to a method of determining a health indication for an ruminant animal, in particular a cow, which method uses a system according to the first aspect of the invention and comprises the steps of obtaining a plurality of 3D images of at least a region of interest of the animal at consecutive points in time during at least a predetermined period of time, processing the obtained plurality of 3D images by the image processing device, determining a region of interest in the plurality of 3D images by the image processing device, calculating for each 3D image a curvature value of the region of interest, and determining the calculated curvature as a function of time, by the control device, and determining points in time when local extreme values of the function of time occur, and the health parameter frequency value by analysing the points in time. Since this is the method counterpart of the system aspect of the invention, it suffices to state here that all special features and advantages mentioned for measures relating to special embodiments of the system aspect of the invention apply as well for the method aspect. 
     It is stressed here that the present method is not a diagnostic method, although it could be used in a diagnostic method. After all, the method only helps in determining whether something could be wrong with an animal. It is not able to make a diagnosis as to what disease is present, if any, in an animal for which a health warning is given. 
    
    
     
       The invention will now be elucidated with reference to one or more exemplary and non-limiting embodiments, as well as to the drawing, in which: 
         FIG. 1  very diagrammatically shows a system  1  according to the invention, and 
         FIG. 2  shows an exemplary plot of the raw curvature versus time, and the smoothed curvature versus time function. 
     
    
    
       FIG. 1  very diagrammatically shows a system  1  according to the invention, for determining a health parameter frequency value for a cow  2 , and comprising a 3D camera  3 , a control device  4  with an image processing device  5 , a milking robot  6  with a teat cup  7 , and a feeding trough  8  with a sensor  9 . 
     A region of interest in the form of the left paralumbar fosse is indicated with reference numeral  10 , and a subregion or window with reference numeral  11 . Other regions of interest, such as the abdomen  10 ′ or the rib cage  10 ″ may also be used. A non-shown camera mover may be controllable by the control device  4  to direct the 3D camera  3  to a desired region of interest. This may be based on a user defined desired health parameter, such as breathing rate which corresponds to a region of interest being the rib cage, or it may be preprogrammed in the control device  4 , that is then arranged to find the desired region(s) of interest based on processing of the obtained images. 
     It is also possible to determine the breathing rate or labour contractions rate, the latter e.g. in a calving pen, by arranging the system, and in particular the 3D camera and/or the control device accordingly 
     In the embodiment shown, there is very diagrammatically shown a milking station, by way of a milking robot  6 , that milks the cow  2  with teat cups  7 , one of which is shown here. As soon as the milking process starts, i.e. after identifying the cow and deciding she will be milked, the control device  4  will be able to estimate roughly the time that the cow will spend at the milking station. For this, she may use a standard, minimum time, historical milking times for the cow, or even an estimated milking time based on production and milking interval, as is per se known in the art. For virtually every milking, this time will be at least 5 minutes, and often up to 8 or 9 minutes. In case the cow will not be milked, she will be urged outside, and there will often not be sufficient time to perform meaningful measurements. 
     Alternatively, the station is a feeding station, indicated diagrammatically by the feeding trough  8 , that has a sensor  9  that indicates the start of eating of the cow, by pressing with its snout. Most milking stations will also have a feeding trough, but it may be a stand-alone system. Yet other alternatives may be a drinking station (or -trough), a treatment station and so on. Also, most stations will have animal identification (not shown here) with which the animal may be recognised and settings (milking, feeding, treatment 0  may be individually adjusted. Furthermore, it is also possible to trigger the 3D camera system by means of this animal recognition, for example if the system should monitor only specific animals. 
     When the 3D camera is turned on, it begins to image (one of) the animal&#39;s region(s) of interest (hereinafter: ROI), here for example indicated as the left paralumbar fossa, indicated by a dashed line  10 . In order to be able to obtain sufficiently reliable data, the frame rate is at least one per second, but preferably at least ten times as high. In order to ensure that the ROI is in view of the camera during imaging, there may be provided a wide-angle lens on the camera, such that while the animal is at or in the (milking, feeding, . . . ) station, the ROI will be in view. It is also possible to provide a motor to move the camera, based on recognition of the ROI in the image by the image processing device  5 . Tracking the ROI in this way is in itself a known technology. The advantage hereof is that the ROI may form a larger part of the image, and may thus be imaged with higher resolution. 
     The obtained 3D images are processed by the image processing device  5 , as will be elucidated further below. The result of the processing is a curvature value for the ROI as a function of time. This function is analysed by the control device  5 , and one or more criteria are applied to determine a health indication for the cow  2 . In case the to health indication gives rise to an alarm or the like, the control device  4  may enter the cow  2  on an attention list, issue an audible or visible alarm, separate the cow  2  after the station  2 ,  6 , or the like. Then, the cow  2  will be examined further, by the farmer or veterinarian. 
     In use of the system, and in the method, the obtained 3D images form a 3D representation of the ROI. In order to limit the number of calculations, to be described below, it is possible to limit the ROI to only a part of, e.g., the left paralumbar fossa, such as to the subregion or window  11  in the present example, although this is not necessary. 
     Instead of determining a depth or volume of this ROI, as is done in prior art systems in order to determine rumen fill, the present invention determines a changing curvature value of the ROI. This is based on the insight that natural processes influence the rumen shape, such that the predictive value of a momentary rumen fill value seems limited, but, contrarily, the predictive value of the analysis of the temporal changes in the curvature of the rumen, or left paralumbar fossa, region seem meaningful. This insight is also useful I determining other health related frequency values, in particular the breathing rate or the labour contractions frequency value. 
     For each obtained 3D image, the (sub)region of interest is tracked by image processing, such as by recognising the top left corner of the left paralumbar fossa, and repositioning/resizing the image. And then a curvature value is calculated. This may be done in many ways, as long as it expresses the degree of curvedness of the ROI in a systematic way. One example will now be elaborated briefly. 
     The determination of the curvature will be limited to the subregion  11 . For this subregion  11 , the curvature value is determined as follows. 
     First, a covariance matrix is calculated from the nearest neighbors of the point. 
     
       
         
           
             C 
             = 
             
               
                 1 
                 k 
               
               ⁢ 
               
                 
                   ∑ 
                   
                     i 
                     = 
                     1 
                   
                   k 
                 
                 ⁢ 
                 
                   
                     ( 
                     
                       
                         p 
                         i 
                       
                       - 
                       
                         p 
                         ¯ 
                       
                     
                     ) 
                   
                   · 
                   
                     
                       ( 
                       
                         
                           p 
                           i 
                         
                         - 
                         
                           p 
                           ¯ 
                         
                       
                       ) 
                     
                     T 
                   
                 
               
             
           
         
       
     
     where k is the number of neighboring points, p i  is the position vector of the i th neighboring point and  p l    is the position vector of the centroid of the neighboring points. The resulting covariance matrix C will be a 3 by 3 matrix with 3 eigenvalues. The surface curvature σ can be estimated by the following equation 
     
       
         
           
             σ 
             = 
             
               
                 λ 
                 0 
               
               
                 
                   λ 
                   0 
                 
                 + 
                 
                   λ 
                   1 
                 
                 + 
                 
                   λ 
                   2 
                 
               
             
           
         
       
     
     where λ 0 , λ 1 , λ 2  are the eigenvalues of covariance matrix C, with λ 0  the smallest eigenvalue. 
     The resulting curvature value σ may then be plotted as a function of time. This is done in exemplary  FIG. 2 , as the somewhat wildly varying curve. Note that the x-axis denotes image number, with in this case a frame rate of 30 Hz, or 1800 images/minute. Clearly, although a rough “beat” is discernible in the curve, it is difficult to extract meaningful information from this. However, it was realised that various sources of noise may be efficiently eliminated. For one, animal movements may be removed, as well as varying lighting conditions, which are in principle one-off variations and not regular variations. In addition, it may be possible to eliminate regular movements that are much faster than the expected contraction frequency, such as breathing. The latter is normally between about 25 and 50 breaths per minute, which is an order of magnitude higher than the reticuloruminal contractions. In this case, the above “noise signals” are removed by means of decomposing the signal by signal frequency, with the “pass” frequency range between 0.5 and 4.0 contractions per minute, and discarding the rest. Thereto, a Fourier transform of the signal was constructed, the pass-frequency range applied with cut-offs below and above the range, and the inverse Fourier transform was constructed, to regenerate a curvature-time function. This function is also plotted in  FIG. 2 , as the smooth curve. In the smooth curve, more or less evenly spaced peaks are clearly visible, and they also clearly have a frequency in the expected range. Note that this smoothed curvature function only serves for visual checks, while the Fourier transformed function serves as the basis for calculations and monitoring. 
     In the smoothed curve, the peaks, or maxima, have been indicated with a dot. The average frequency, thus for the reticuloruminal contractions, is about 94=5800/1800)=2.8 contractions per minute. This is a normal frequency for the tested cows, in this case primiparous healthy Holstein and Swiss-Brown cows, so for this particular cow, a “healthy” indication may be given, and no health alarm need be given. 
     However, it is possible that a particular cow usually has a higher or lower value, based on historical measurements. In such a case, an health indication “still healthy, but check” may be given, i.e. some examination may be performed, but not very urgent, or the cow could be monitored more closely. It is also possible that the calculated contraction frequency is actually lower than a predetermined threshold value, such as when the determined frequency is between about 1 and 2 per minute during feeding. Such a value is not uncommon during resting, but should normally be higher during feeding. Therefore, in such a case the health indication “check urgently” may be issued by the control device, or an alarm sounded etc. 
     It is remarked here that it may have further advantages to determine more than one health parameter frequency value, in that knowing such values allows to remove the corresponding signal(s) from the other signal(s) being determined. For example, if the to system is set to monitor labour contractions, a problem may be that these occur much more infrequently than breathing or reticuloruminal contractions, even though these occur primarily in other parts of the body. By determining the rumen motility (frequency value) and/or the breathing (rate), and subtracting any residual signal(s) that correspond(s) to these movements from the abdominal observation, the resulting abdominal images may result in a more reliable determination of the labour contractions frequency value. 
     In the embodiment shown, there is provided a 3D camera system in a milking station. The animal will be milked in the station a few times per day, such as 2-4 times/day. It is advantageous if the animal is monitored more often, because e.g. the measurement could fail, due to a too short time to conclude to meaningful information, or because of too violent movements or the like. Therefore, it is advantageous if the 3D camera system comprises one or more additional cameras in other positions, such as feeding stations, watering stations, or even cubicles or “resting stations”. Note that the determined frequency may be compared with a correspondingly adapted threshold frequency, such as a lower threshold frequency when in a cubicle. 
     It is noted that the 3D camera generates 3D images, which represent a 2D image of the animal combined with, for each pixel, information about the distance to the camera. In the above embodiment, the curvature was calculated in a region of interest, and conclusions were drawn based on a time analysis of the curvature. It is also possible that the control device, with the image processing device, calculates the distance between a specific point in the region of interest and the camera. This point will also move towards the camera and back again, with the same frequency as the curvature changes. In other words, the relative position of the point with respect to the camera changes, with the same relevant frequency. Thus the present invention, both system and method, could also function when they (are arranged to) measure the relative position of a fixed point in the region of interest (e.g. left paralumbar fossa or subregion thereof), and analyse the extremes, in particular the points in time when the fixed point is closest to the camera. 
     It is advantageous when this fixed point is determined with a sufficient precision and accuracy, in order to prevent artefacts or simply mismeasurements. Thereto, it is advantageous if the fixed point is easily recognisable in the image. Herein, it is helpful to determine the boundaries of the paralumbar fossa, which is a relatively easily recognisable triangle on the left side of the animal. The fixed point may then be determined by the image processing software to be in a relative position to the boundaries of the thus determined region of interest, such as in the geometric centre, or any other position. It is then relatively straightforward, even when performing the analysis afterwards instead of in real time, to determine a basic position of the animal by using the relative positions of the boundaries of the region (such as the ribs and the backbone in the case of rumen motility, and additionally indicating that it is advantageous to determine breathing rate, in order to subtract the corresponding signal). Movements of these boundaries as a whole count as displacements of the animal as a whole and are meaningless as to the health related movements or contractions. After subtracting these whole animal movements, and if possible also signals corresponding to other health related movements, or otherwise accounting therefor, the true relative movement of the fixed point may be determined, and the rest of the analysis may more or less be copied for that relative movement. 
     The above described embodiments only serve to help explain the invention without limiting this in any way. The scope of the invention is rather determined by the appended claims.