AU2011332359A1 - An oestrus detection tag and method and system - Google Patents

Abstract

An oestrus detection tag includes a monitoring device and a body suitable to be secured to the back of an animal. The monitoring device has an exposed modifiable element, which changes in response to animal interaction with the modifiable element. A signal generated by the monitoring device is dependent upon the condition of the modifiable element.

Description

WO 2012/070958 PCT/NZ2011/000246 1 AN OESTRUS DETECTION TAG AND METHOD AND SYSTEM FIELD OF THE INVENTION 5 This invention relates to an apparatus for detecting oestrus in animals, in particular but not exclusively cows. The invention also relates to a system and method for detecting oestrus in animals. BACKGROUND OF THE INVENTION 10 Oestrus is the phase of certain animals' reproductive cycles which indicate they are ready to be fertilised. In common parlance, this is referred to as the animal being 'in heat'. Oestrus can be evidenced by various changes in the animal, which will depend on the species of animal concerned. These 15 include physiological changes and visibly observable behavioural changes. For example, it is common knowledge that oestrus in a cow will provoke other cattle to mount the back of the cow, regardless of whether the mounting animal is itself in oestrus. Therefore, a cow being mounted is a strong indicator that the cow is in oestrus. 20 In the context of farming, accurate detection of when an animal is in oestrus is important as it allows for efficient fertilization of the animals to take place. Further, in the context of dairy farming, it ensures that a cow produces offspring at the first opportunity, maximising the time that the specific cow is 25 producing milk. It also minimises undue expense in the context of artificial insemination programs. Due to the significance of oestrus detection, various apparatus and methods for detecting oestrus have been developed. Some methods for detecting 30 oestrus do not rely on the.mounting behaviour, such as those which detect WO 2012/070958 PCT/NZ2011/000246 2 increased pacing of the animal. Whereas others, as outlined below, detect the mounting behaviour itself. The most basic rely on a person observing the actual mounting taking place. 5 This is highly inefficient for obvious reasons. Another commonly used method is the painting of the tail areas of a cow. When the cow is mounted the paint is abraded. Such abrasion is then observable by a person, who can check the herd at regular intervals. Though 10 this method minimises the requirement for constant observation, it still relies on regular human observation. Also, the paint is susceptible to abrasion due to other activities of the cow, and therefore may lead to many false positives. A further advancement of the tail paint concept is outlined in patent 15 specification NZ 547988, which describes an 'oestrus indicator patch' which is secured to the back of the animal. The patch includes a reflective layer covered by a non-reflective layer; the reflective layer being revealed by the abrasion of the non-reflective layer. Though such rub strips have been the subject of earlier patents (for example, US 6,467,430) the patch includes a 20 'reference area' which lends the patch to automatic visual detection (by means of a camera or the like). Even more complicated systems exist, including patches which include electronic circuitry. An example of this is outlined in patent specification NZ 25 501444, which describes an oestrus indicator which is a passive transponder that is partially destroyed by a fluid escaping from a vial when the animal is mounted. The most advanced systems implement some degree of automation, which 30 minimises the requirement for human observation of a tag. For example, WO 2012/070958 PCT/NZ2011/000246 3 patent specification NZ 528756 broadly describes many possible systems for sensing and indicating oestrus. The focus of the specification is the automatic detection of the state of the oestrus indicator, which requires complicated visual detection systems. 5 The problems arising from the various prior art systems are that they can be unreliable and expensive. Some also rely on farmers implementing new technologies at significant cost. 10 It is an object of the invention to provide an improved system, method or apparatus for detecting oestrus in animals or to at least provide the public with a useful choice. SUMMARY OF THE INVENTION 15 According to one exemplary embodiment there is provided an oestrus detection tag including a body which is suitable to be secured to the back of an animal and a monitoring device having an exposed modifiable element, which changes in response to animal interaction with the modifiable 20 element, wherein a signal generated by the monitoring device is dependent upon the condition of the modifiable element. According to another exemplary embodiment there is provided a system for detecting oestrus in an animal comprising an oestrus detection tag having a 25 body suitable to be secured to the back of an animal and monitoring device having an exposed modifiable element, wherein a signal generated by the monitoring device is dependent upon the condition of the modifiable element, and a detector for monitoring the signal generated by the monitoring device. 30 WO 2012/070958 PCT/NZ2011/000246 4 According to a further exemplary embodiment there is provided a method of detecting oestrus in an animal comprising the steps of applying an oestrus detection tag including a monitoring device having a modifiable element, the condition of which alters a signal generated by the oestrus detection tag and 5 detecting the signals generated by the monitoring device to infer the condition of the modifiable element and thus the animal. It is acknowledged that the terms "comprise", "comprises" and "comprising" may, under varying jurisdictions, be attributed with either an exclusive or an 10 inclusive meaning. For the purpose of this specification, and unless otherwise noted, these terms are intended to have an inclusive meaning - i.e. they will be taken to mean an inclusion of the listed components which the use directly references, and possibly also of other non-specified components or elements. 15 Reference to any prior art in this specification does not constitute an admission that such prior art forms part of the common general knowledge. BRIEF DESCRIPTION OF THE DRAWINGS 20 The accompanying drawings which are incorporated in and constitute part of the specification, illustrate embodiments of the invention and, together with the general description of the invention given above, and the detailed description of embodiments given below by way of example only, serve to 25 explain the principles of the invention. Figure 1 shows an isometric representation of the oestrus detection tag; Figure 2 shows an exploded side view schematic of the oestrus detection tag; WO 2012/070958 PCT/NZ2011/000246 5 Figure 3 shows a circuit diagram for a monitoring device according to one embodiment; Figure 4 shows a circuit diagram for a monitoring device according to another embodiment; and 5 Figure 5 shows a schematic representation of a system for detecting oestrus. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 10 Referring to figure 1, there is shown an oestrus detection tag 1 according to a first embodiment. The tag includes a body 2 and a monitoring device 3. The monitoring device includes a modifiable element 4. The oestrus detection tag 1 is designed to be secured to the back of an 15 animal. In this way, the tag, by means of other aspects of the invention described later, is able to detect mounting of one animal by another animal. Such mounting can be indicative of the mounted animal being in oestrus. The remainder of this description will refer to the use of the invention in respect of cattle, however the invention is not limited in this way and those 20 skilled in the art will appreciate that the invention is applicable to any breed of animal which demonstrates oestrus behaviour that is analogous to cattle. The means of securing the tag, according to a first embodiment, is by means of an adhesive, such adhesive typically being glue manually applied to the 25 cow and or the tag. Alternatively a self-adhesive layer may be attached to the tag during manufacture. A releasable line may be applied to protect the self adhesive layer up to the time of application.

WO 2012/070958 PCT/NZ2011/000246 6 The adhesive may be a pressure sensitive adhesive. The adhesive may be attached to the other tag layers by hot melt or solvent based adhesion. The adhesive may be acrylic-based or rubber-based, or any other suitable adhesive may be used. The adhesive may be around 120 microns thick. 5 In general the adhesive should have a high tack and peel strength and high water resistance. This helps the tag to stay in place despite exposure to rain and to various forces tending to detach the tag from the animal. 10 In one embodiment the tag may exhibit adhesion exceeding the following minimum standards: according to standard ASTM D330 180 Peel Test (as at 18 November 2011) a minimum of 50N/25mm; and according to standard ASTM D3654 Shear test (as at 18 November 2011) Procedure A, a minimum of 2 minutes. 15 It will be appreciated by those skilled in the art that there are many suitable adhesives and other possibilities for securing the tag to the animal, and the invention is not limited to any particular means. 20 Similarly, those skilled in the art will appreciate that the location where the tag is secured on the back of the animal is not limited to a precise region (such as the spinal ridge of the rump area) and can be secured anywhere where the tag will be susceptible to the mounting action of another cow. 25 The tag preferably has sufficient flexibility to conform to the shape of the animal's shape. Referring to figure 2, there is shown an exploded side view of an embodiment of the oestrus detection tag 5. The tag has a monitoring device 6 30 including base layer 6a, modifiable element 7 and connections 13 14. Figure WO 2012/070958 PCT/NZ2011/000246 7 2 also illustrates the body 8 of the tag, and the layer of adhesive 9, used to secure the tag to the back of the cow. In a preferred embodiment the tag also includes a protective layer 10, a visual undercoat 11 and a visual topcoat 12. The protective layer serves to protect the part of the monitoring device 5 contained beneath it. The visual undercoat and visual top coat provide additional protection, whilst also allowing a backup method of detecting oestrus, should the monitoring device fail. The visual undercoat and visual topcoat may be provided, for example, with contrasting colours. The visual topcoat and modifiable layer may be formed as a single layer. 10 As is clear from this drawing, the modifiable layer may be covered by a topcoat layer and still be considered "exposed" for the purposes of this specification. The term "exposed" applies to modifiable layers that are susceptible to modification through abrasion, rubbing, scratching or similar 15 physical processes. Similarly, the modifiable layer may be modifiable through abrasion, rubbing, scratching or similar physical processes. The layer immediately beneath the modifiable layer (in this embodiment the visual undercoat 11) may be formed with a smooth or gloss finish such that 20 the modifiable layer is more easily removed from the tag. The modifiable element 7 may be formed from any suitable material, including a conductive material, conductive foil, conductive ink, conductive paint or conductive liquid. Conductive foil may be hot or cold stamped. 25 Other suitable materials may occur to the skilled reader. In one embodiment the tag may be a square or rectangular tag with side lengths between 40 and 120 mm.

WO 2012/070958 PCT/NZ2011/000246 8 In general, any suitable modifiable element may be used. For example, the modifiable element may be in the form of a planar surface that is not electrically connected to the signalling circuitry. Alternatively, the modifiable element may be in the form of a planar surface that is electrically 5 connected to the signalling circuitry. In further alternatives, the modifiable element may be a modifiable circuit, circuit element or loop, either electrically connected to the signalling circuitry or not. The modifiable element may act as a block or shield, or may be part of the signalling circuitry. The modifiable circuit may act as an electromagnetically coupled 10 circuit to alter the response of the signalling circuitry. Many suitable arrangements may occur to the skilled reader. The monitoring device changes in response to the mounting of the cow. Such mounting will interact with and interfere with the modifiable element 7 15 (which is a part of the monitoring device 6 itself) and will therefore affect the operation of the monitoring device, in particular the signal which is generated, as discussed below. In this way, the monitoring device detects mounting. 20 The modifiable element 7 is configured to be sensitive to the mounting action. In a preferred embodiment, the modifiable element 7 has two discrete states: the first state being an uninterfered state before any mounting has taken place; and the second being an interfered state following mounting. In another embodiment, the modifiable element 7 has multiple discrete states, 25 where a particular state will evidence the frequency and or intensity of the mounting activity. In a further embodiment, the modifiable element 7 has a range of continuous states, where the state will evidence the frequency and or intensity of the mounting activity.

WO 2012/070958 PCT/NZ2011/000246 9 For those embodiments which allow discrete states, the'modifiable element will be a link 7 (or links, in the case of multiple discrete states) between two other parts of the monitoring device 6. These links are severed by the action of the mounting cow. In a preferred embodiment, the monitoring device 5 includes electronic circuitry and the link joins two parts of the circuit by means of electronic connections 13 and 14. When the link is broken, it affects the operation of the remaining circuitry in the monitoring device and will affect the signal generated by the monitoring device 6, as discussed below. 10 In a preferred embodiment, the link (or links) is a conductive ink line applied to an upper layer of the tag, whilst connected to the remainder of the monitoring device below. The conductive ink line is exposed to the mounting cow, and will be removed on account of the abrasive action and 15 this will sever the link. In another embodiment, the modifiable element is not exposed directly to the mounting cow due to the presence of the visual topcoat 12, in which case the tag is configured such that mounting causes the visual topcoat and the modifiable element 7 to be removed. In a further embodiment, the link is a frangible connection such as a wire, with the 20 mounting action severing the wire irreversibly. Mechanisms for piercing the circuit or causing a mechanical displacement that results in a short or open circuit may also be used. 25 For those embodiments which allow continuous states, the modifiable element 7 comprises a part of another piece of circuitry in the monitoring device (such as a capacitor or inductor). In one embodiment, the modifiable element 7 is a conductive ink layer printed on the top of the tag, and this functions as one plate of a capacitor (with the second plate protected from 30 mounting beneath a dielectric layer). Thus, as the cow is mounted, the WO 2012/070958 PCT/NZ2011/000246 10 conductive ink plate is gradually erased which in turn gradually alters the capacitance of the capacitor. The circuitry in the monitoring device 6 is configured to allow this to affect the generation of a signal by the monitoring device. 5 The monitoring device 6 generates a signal that is detectable by a suitable detector. According to a preferred embodiment the monitoring device is configured to receive and emit signals using an electromagnetic field, in particular in the radio frequency range. However, other similar wireless 10 technologies could also be used as the basis for the monitoring device 6, including electronic article surveillance (EAS) tags, RFID tags, resonant circuit, mechanical, electrical, optical, electro acoustic, magnetic and acousto-magnetic technologies. The device may provide a signal in any suitable frequency range. 15 Where EAS tags and readers are used, non-deactivatable tags are preferred. Most EAS tags are deactivated by a high field strength from 'a standard reader (e.g. if the tag is too close to a reader or to a dedicated deactivator). In some applications this is a desirable feature. However, in oestrus detection it is 20 undesirable. Change in the tag signal should be caused by modification of the tag, not deactivation in this manner. Various tag technologies can also be adversely affected by the close proximity of some substances, such as conducting materials or water. This 25 can lead to de-tuning through capacitive, electrostatic or electromagnetic coupling, or the loss of resonant response caused by parasitic losses. Where this problem is encountered, tags or tag components may be water-proofed and may be appropriately protected using barriers, spacers or packers separating the tag or the particular component from other components. 30 WO 2012/070958 PCT/NZ2011/000246 11 In a preferred embodiment, the monitoring device 6 is a passive transponder. Other types of transponders would also be suitable for use in the invention, such as active transponders and radio frequency identification (RFID).tags, including devices with an encoded identification number. These alternative 5 implementations are consistent with the invention herein disclosed and those skilled in the art will appreciate how such alternatives could be used in the context of this invention. In a preferred embodiment, the passive transponder is a simple parallel 10 resonant circuit, which includes at least one capacitor and at least one inductor. Such a circuit is ideal as it is cheaper to make and less likely to malfunction than other more complex circuits which perform essentially the same function. Included in the resonant circuit is the modifiable element (described above). The modifiable element 7 may be a separate component 15 of the circuit or it may be part of a capacitor or inductor. In one preferred embodiment the monitoring device, as represented by the circuit diagram in figure 3, includes an inductor 15, a capacitor 16 and a modifiable element 17. The modifiable element 17 is shown in the interfered 20 state. Prior to interference, the modifiable element completes the circuit, being a basic LC circuit. Such an LC circuit has the property of having a resonant frequency, which is detectable by a suitable detector. In this embodiment, the circuit is passive, so the circuit must first be energised by means of inductive coupling with the inductor 15. If the modifiable element 25 17 is in the interfered state, the circuit is broken and the LC circuit will not have a resonant frequency. Thus, the signal generated by the monitoring device is dependent on the condition of the modifiable element. In another preferred embodiment the monitoring device as represented by 30 the circuit diagram in figure 4, includes an- inductor 18, a capacitor 19 and a WO 2012/070958 PCT/NZ2011/000246 12 modifiable element 20. This embodiment acts in the opposite manner to the embodiment shown in figure 3 and described above. The modifiable element 20 is connected in parallel with the capacitor 19, and when in the uninterfered state, causes no charge to build up on the capacitor. Thus the LC 5 circuit is dampened. Once the modifiable element 20 is interfered with, the LC circuit will resonate so as to be detectable by a suitable detector. Thus the signal generated by the monitoring device is dependant on the condition of the modifiable element 20. 10 The above describes two basic circuits as they serve to demonstrate the principles of the invention. However, the inventions not limited to these examples, and it will be appreciated by those in the art that any suitable array of circuit components may perform essentially the same function. For example, it is possible to configure the circuit such that the change of state 15 varies between two distinct frequencies. Another example, in the context of a modifiable element with a range of discrete states, the links may each be in series with an additional circuit component, and thus as the links are severed, the corresponding circuit 20 component is removed from the circuit, changing the operation of the monitoring device. The modifiable element need not be conductively coupled to the other elements of the device to have the influence required to produce a detectable 25 signal. For example connectivity could be by electromagnetic or electrostatic coupling causing a detectable signal through transformer or eddy current effects. Another aspect of the invention is a system for detecting oestrus as shown in 30 figure 5. The system includes an oestrus detection tag 22 which is secured to WO 2012/070958 PCT/NZ2011/000246 13 the back of a cow 21, a reader including a transmitter 23 and a detector 24. The transmitter and detector are connected to a processor 25 by suitable means, which in turn is connected to an automatic drafting gate 26 and a database 27. The transmitter and detector can be contained within a suitable 5 device (such as a handheld scanner) or may be mounted in a suitable location so as to interact with the oestrus detection tag as the cow passes by. In general any suitable reader may be used for the type of tag used. In some embodiments the reader may read tags within a constrained detection zone, e.g. around 200mm to 1000mm from the reader. This provides a satisfactory 10 read range while reducing the opportunity for a large number of tags to be read at once. Preferably the reader systems used have no dead zones in the target space. The transmitter 23 and detector 24 are configured in accordance with the 15 specifications of the oestrus detection tag. Thus, in a preferred embodiment the oestrus detection tag is a radio frequency resonant circuit and the detector 24 is configured to detect radio frequency electromagnetic waves. Similarly, the transmitter 23 is configured to transmit radio frequency electromagnetic waves. 20 The transmitter 23 performs two functions. The first is to transmit an energising field. In some embodiments, the monitoring device may not have an internal power source, in which case an energising field is needed to activate the monitoring device. In a preferred embodiment, the energising 25 field is an electromagnetic field of suitable frequency, which will (by the process of inductive coupling) cause a potential difference to be established across the inductor within the monitoring device. The second function of the transmitter 23 is to transmit an interrogating field. 30 In the context of the system which employs a radio frequency resonant WO 2012/070958 PCT/NZ2011/000246 14 circuit, the field is a suitable electromagnetic signal to create a resonant frequency within the monitoring device (with such resonance being detected by the detector). Energising and interrogating fields may be provided by the same RF signal. 5 The transmitter 23 and detector 24 are connected to a processor 25. The processor 25 may be contained within the same device as the transmitter 23 and the detector 24 or may be within a separate device but connected by suitable means, for example by a wired or wireless connection. The 10 processor 25 is configured to analyse the signals which are sent and detected by the transmitter 23 and detector 24. In accordance with the specifications of the oestrus detection tag 22 the processor is alerted to the change in the modifiable element and thus may infer oestrus in the animal to which the tag is secured. The processor 25 may also be configured to process additional 15 information, such as cow identification data (which is typically contained within another device attached to the cow's ear). Thus, the processor can relate cow identification information to positive oestrus detection. In a preferred embodiment, the processor 25 is connected to an automatic 20 drafting gate 26. The drafting gate is configured such that in the case of positive oestrus detection, the automatic drafting gate can cause the cow in oestrus to be separated from the remaining stock. This enables automatic isolation of those animals which require fertilisation. 25 The processor 25 is also connected to a database 27. In a preferred embodiment, oestrus detection results and cow identification data are suitably stored within an electronic database 27. The database 27 can be configured to process and display the data in a means which is helpful to the user. For example, it may be possible to quickly and efficiently map the WO 2012/070958 PCT/NZ2011/000246 15 oestrus cycles for a particular cow which enables more accurate predictions of the next onset of oestrus to be made. The reader is preferably a device with excellent noise performance. The 5 reader antenna may be of any suitable configuration, including figure of 8 and triple loop antennas. The reader or separate processing circuitry may employ noise filtering or cancelling steps. A further aspect of the invention is the method of detecting oestrus in 10 accordance with the system herein described and shown in figure 5. The oestrus detection tag 22 is secured to the back of the cow 21 in accordance with the specifications of the tag. Finer details of the method of securing the tag can be left to the discretion of the farmer, who may find 15 through experience, for example, that a certain tag site yields better quality results. At some later time, the farm operator can choose to investigate the state of the oestrus detection tag 21, for example during daily stock checks. Again, 20 the details of when and how to undertake the checks is left to the discretion of the farmer as it is dependent on the operations that they are running. In a preferred embodiment, the stock are brought into a race which compels the cows to move in single file. At some point along the length of the race, 25 there is placed a detector 24 and transmitter 23. They can be suitably attached to a post or the like, or they can be held by a person if the device is handheld. As the cow passes, the transmitter 24 is initiated to transmit a suitable 30 energising field (if the monitoring device is passive). Then, the transmitter 23 WO 2012/070958 PCT/NZ2011/000246 16 is made to transmit a suitable interrogating field. Lastly, the resulting field is detected from the monitoring device by the detector 24. The transmitted and detected signals are processed by a processor 25. The processor is configured in accordance with the specifications of the oestrus detection tag, to analyse 5 the transmitted and detected signals to determine the state of the modifiable element. If the result indicates that the modifiable element has been broken, this implies that the cow is in oestrus. For the simplest detection it is desirable to cause a significant change in the 10 signal characteristics (e.g. signal on/off, signal strength, signal frequency etc) of the tag. Subtle changes in signal' characteristics are less useful, as they may be caused by various factors, such as scratching against trees, or water, or distance from the reader. 15 A large area modifiable element and the use of highly conductive materials contributes to the magnitude of the change. Where the modifiable element couples to the tag circuit, this coupling should be strong in order to maximise the change caused by modification. This can be achieved by suitable matching of geometry etc. In addition, the modified tag should couple 20 strongly to the reader. The modifiable element may be altered undesirably due to scratching against trees or stockyards or other solid objects. For this reason, it may be desirable to provide a threshold for the oestrus determination. This may be achieved 25 by any one or more of the following mechanisms. A modification threshold may be used. For example, the modifiable element may be in the form of a single planar layer. Scratching of small areas will cause some modification, but only once a sufficiently large area has been 30 modified will the threshold be exceeded. This may be reflected in a signal WO 2012/070958 PCT/NZ2011/000246 17 strength passing a threshold (being either stronger or weaker than the threshold). Alternatively, this may be reflected in a signal frequency passing a threshold (either a lower or a higher frequency), or in some other signal characteristic passing a threshold. 5 The modification element may include a number of distributed modification areas. In this embodiment all, or a threshold number, of the modification areas must be modified in order to cause a determination that the animal is in oestrus. In one embodiment all modifiable areas must be modified, but in 10 other embodiments a lower threshold may be used. The device may require that more than one circuit or circuit element needs to be modified. For example, in one embodiment a threshold number of circuits must be disrupted in order to cause a determination that the animal is 15 in oestrus. The device may include both distributed modification areas and a plurality of modifiable circuits or circuit elements. Such circuit patterns may include multiple areas and/or pathways. 20 There is thus provided an oestrus detection tag which is cheap to make and simple to implement. Similarly, there is provided a system and method for implementing the same, particularly in the context of cattle operations. 25 While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the 30 invention in its broader aspects is not limited to the specific details, WO 2012/070958 PCT/NZ2011/000246 18 representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of the Applicant's general inventive concept.

Claims (36)

1. An oestrus detection tag including: a. a body suitable to be secured to the back of an animal; and b. a monitoring device having an exposed modifiable element, 5 which changes in response to animal interaction with the modifiable element, wherein a signal generated by the monitoring device is dependent upon the condition of the modifiable element.

2. The oestrus detection tag as claimed in claim 1, wherein the monitoring 10 device is a radio frequency transponder.

3. The oestrus detection tag as claimed in claim 2, wherein the radio frequency transponder is a resonant circuit having circuit components including: a. a first capacitor; 15 b. a first inductor; and c. the modifiable element.

4. The oestrus detection tag as claimed in claim 3, wherein the resonant circuit is arranged such that the operation of the resonant circuit is dependent upon the condition of the modifiable element. 20

5. The oestrus detection tag as claimed in claim 4, wherein the modifiable element is connected between two points in the resonant circuit such that a current in the resonant circuit is dependent upon the condition of the modifiable element.

6. The oestrus detection tag as claimed in claim 4, wherein the modifiable 25 element has a first state, which permits a current, and a second state, which does not permit a current. WO 2012/070958 PCT/NZ2011/000246 20

7. The oestrus detection tag as claimed in claim 3, wherein the modifiable element is at least partly formed from conductive ink or conductive paint.

8. The oestrus detection tag as claimed in claim 3, wherein the modifiable 5 element is an exposed frangible connection.

9. The oestrus detection tag as claimed in claim 3, wherein the modifiable element is not conductively coupled to the resonant circuit.

10. The oestrus detection tag as claimed in claim 3, wherein the circuit is modified by dislocation or piercing 10

11. The oestrus detection tag as claimed in claim 6, wherein when the modifiable element is in the first state, the resonant circuit is inoperative and when the modifiable element is in the second state, the resonant circuit has a resonant frequency, which is detectable by suitable means.

12. The oestrus detection tag as claimed in claim 6, wherein when the 15 modifiable element is in the first state, the resonant circuit has a resonant frequency, which is detectable by a suitable means, and when the element is in the second state, the resonant circuit is inoperative.

13. The oestrus detection tag as claimed in claim 6, wherein when the modifiable element is in the first state, the resonant circuit has a first 20 resonant frequency, which is detectable by a suitable means, and when the element is in the second state, the resonant circuit has a second resonant frequency, which is detectable by suitable means.

14. The oestrus detection tag as claimed in claim 2, wherein the radio frequency transponder is a resonant circuit having circuit components 25 including: a. a first capacitor; and WO 2012/070958 PCT/NZ2011/000246 21 b. a first inductor; wherein the modifiable element is a contributory part of the first capacitor or the first inductor.

15. The oestrus detection tag as claimed in claim 14, wherein the 5 modifiable element operates as a capacitive plate of the first capacitor.

16. The oestrus detection tag as claimed in claim 15, wherein the modifiable element is a layer of conductive ink

17. The oestrus detection tag as claimed in claim 16, wherein the modifiable element has a range of indiscrete states, dependent on how 10 much of the layer of conductive ink has been removed.

18. The oestrus detection tag as claimed in claim 17, wherein the resonant circuit is arranged such that the operation of the resonant circuit is dependent upon the condition of the modifiable element and wherein the resonant circuit has a frequency, which is detectable by suitable 15 means, according to the indiscrete state of the modifiable element.

19. The oestrus detection tag as claimed in claim 1, wherein the monitoring device uses a non-contact electromagnetic signalling method.

20. The oestrus detection tag as claimed in claim 19, wherein the signalling method is based on low frequency magnetic saturation 20

21. The oestrus detection tag as claimed in claim 19, wherein the signalling method is based on magnetoelastic resonance.

22. The oestrus detection tag as claimed in claim 1, wherein the body is made of plastic or card.

23. The oestrus detection tag as claimed in claim 1, wherein the body is 25 secured to the back of an animal by means of an adhesive. WO 2012/070958 PCT/NZ2011/000246 22

24. A system for detecting oestrus in an animal comprising: a. an oestrus detection tag having a body suitable to be secured to the back of an animal. and monitoring device having an exposed modifiable element, wherein a signal generated by the 5 monitoring device is dependent upon the condition of the modifiable element; and b. a detector for monitoring the signal generated by the -monitoring device.

25. The system for detecting oestrus as claimed in claim 24, wherein the 10 system includes a transmitter for generating an exciting field.

26. The system for detecting oestrus as claimed in claim 25, wherein the exciting field is an electromagnetic field in the radio frequency spectrum.

27. The system for detecting oestrus as claimed in claim 26, wherein the 15 exciting field is configured to inductively couple with the oestrus detection tag, causing the monitoring device to become energised.

28. The system for detecting oestrus as claimed in claim 24, wherein the system includes a transmitter for generating an interrogating field.

29. The system for detecting oestrus as claimed in claim 28, wherein the 20 interrogating field is an electromagnetic field in the radio frequency spectrum.

30. The system for detecting oestrus as claimed in claim 29, wherein the interrogating field is configured to inductively couple with the oestrus detection tag and interact with the monitoring device. WO 2012/070958 PCT/NZ2011/000246 23

31. The system as claimed in claim 27 or claim 30, wherein the detector is configured to detect the signal generated by monitoring device as a result of the exciting field and or the interrogating field.

32. A method of detecting oestrus in an animal comprising the steps of: 5 a. applying an oestrus detection tag including a monitoring device having a modifiable element, the condition of which alters a signal generated by the oestrus detection tag; and b. detecting the signals generated by the monitoring device to infer the condition of the modifiable element and thus the 10 animal.

33. The method of detecting oestrus as claimed in claim 32, wherein the method includes the step of transmitting an exciting field using a transmitter in order to energise the monitoring device.

34. The method of detecting oestrus as claimed in claim 32, wherein the 15 method includes the step of transmitting an interrogating field using a transmitter in order to interact with the monitoring device.

35. The oestrus detection tag as claimed in claim 1 further including a visual topcoat and a visual undercoat, configured such that the visual undercoat is exposed through physical damage or removal of the visual 20 topcoat, thereby providing a visual indication of oestrus.

36. The oestrus detection tag as claimed in claim 35 wherein the visual topcoat is provided by the modifiable element.