With average costs of roughly 1.50€ per each tag, it is the cheapest method among the three. However, it suffers from one disadvantage which could lead to several problems. Its application to the ear lobe of the sheep increases its possibility to be lost due to entanglement in bushes, trees fences, etc. Another problem has to do with the ease of removal of the tag, a practice used in various fraudulent activities regarding animal identifications and could be avoided using irremovable animal tagging systems. In case of tag losses, new tags are to be applied, which not only causes additional administrative work but also impacts the welfare of the sheep which have to undergo another piercing of the ear.In this case, the EID is enclosed in a ceramic bolus, which is then inserted into the sheep’s rumen using a designated tool . Although having a slightly higher cost of about 4–5€, its main advantage is its permanence and very low malfunction and loss rate. Boluses have widespread use and are currently applied routinely in many commercial farms. It is however a more complicated EID to insert, with sheep needing to reach a certain age in order to safely receive the bolus. Size reduction and proper insertion by trained personnel mitigate these problems, with the bolus total size and length being a key factor. As shown by Hentz et al. , smaller boluses could be inserted safely and efficiently to smaller ewes while retaining the internal positioning and reliability.Widely used in house pets and horses for animal identification, its use in livestock although permitted is very limited . The main reason for its limited use is the difficulty to remove the EID in the abattoir,and the tendency of early models to migrate from the original region of injection.Different studies however show limited migration patterns of modern glass and silicone enclosed injectable EIDs during their use in field conditions.A particular advantage of injectable EID is the possibility of it being used not only as passive information storage but also as a sensor for physiological parameters.
The use of temperature detecting injectable passive RFID/ EIDs is widespread in the management of smaller laboratory animals and was tested on bigger farm animals under different conditions . Its use in sheep has been shown to provide highly correlating data to that of core temperature measured via rectal thermometry. This concept is, however, stackable flower pots still in the experimental stage and its future applications are uncertain.Sensors applied on the individual animal are one of the key principles of PLF with tools such as pedometers and rumination tags are well known to dairy cattle farmers. They provide information on animal’s physiological conditions whether in real time or via data loggers downloading in key passages . These sensors collect data from the animal and translate it into physiologic status such as ovulation or lameness relevant to farm management . In case of extensive sheep farming, wearable sensors have been experimented in small-scale-controlled conditions as well as experimental farms . The main objectives of these sensors are to evaluate grazing and resting behaviours, which provide information regarding grazing patterns and feed intake as well as animal position and movement of the flock . Currently, two main types of technology are being tried in this field: accelerometers, especially the tri-axial type, and GPS systems. The third use of active sensors is in the case of social networks and behaviour such as heat and mating identification. Being a seasonal breeding species, a big focus in Mediterranean production is dedicated to out of the season mating in order to maintain constant milk production in contrast to the sheep’s natural cycle . Currently, a common practice is the use of a harness on the flock rams with colour for visual identification of covered ewes; however, the use of electronic activity logger is being tested .A system that measures movement in terms of the direction and speed of the sensor is attached to the foot, neck or head of the sheep. Evaluated by the software first, data are provided to the producer to assist in decision making .
The most useful data come from three axial accelerometers which record movement in a three-dimensional pattern. Field trials confirm the ability of such accelerometers to register movement patterns linked to behaviours such as resting, grazing, moving and running/playing or lameness . Even though accelerometers could be considered technologically matured, data interpretation and validation is still a subject for field research . Meanwhile, the collection and management of the data as well as energy supply to systems in the field present a big challenge for a widespread application. In recent years, the amount of research put into this system is growing increasingly especially in attempt to take a research ready prototype into commercial production . Therefore, accelerometers could represent in the near future a viable product.Especially when paired with geographic information system , it provides information on animal movement and disposition in certain geographical areas. Such a system could help evaluate the movement of sheep in a vast grazing area, between water sources, low and high land and in response to the presence of predators or wild herbivores . In the work of de Virgilio et al. , combined use of accelerometers and GPS/GIS was proposed as a PLF option for sustainable range land management. Such systems, however, are not yet operational in commercial farming due to relative high cost of each sensor and the need for high energy supply . Also, information gathered by the systems still needs interpretation and given the right value in a decision-making process.In a recent study by Mozo et al. , tri-axial was used accelerometer with specific software to detect rams’ mating activity providing a possible tool to measure service capacity of rams. A more mature system is the electronic Alpha-Detector which includes a harness for the ram with an active reader and transmitter which detects the ewes’ EID and transmits the data to a centralized computer. The transmitted data could be interpreted for frequency of mating, true and false coverings and the number of ewes covered. This system has currently passed the research phase and is being tried in field conditions for commercial production .
Other technologies include a concept produced by Laca regarding extensive management of animals which incorporates GPS, satellite communication of data from ‘mother collars’, short distance communication between the animals’ collars and feed management based on the elaborated data. The system is very complex and requires both costly technologies and knowledge of the herd dynamics for the identification of key individuals in their respective groups . The feasibility of such system is becoming widespread in Mediterranean dairy sheep farming due to cost and complexity, but may be relevant for other types of extensive farming that use larger grazing areas , or less contact with the animal . Other sensors include microphone and sound analysis of chewing sheep and monitoring urination in sheep and cattle in order to determine liquid and nitrogen emissions. However, the systems were only described as an experimental process and not yet ready for field implementation.Stationary sensors are another key element in the PLF concept, with different types of sensors such as temperature sensors, cameras, weights and automatic feeders are placed in key locations of a barn . These sensors collect data and usually communicate with the animals’ EIDs, providing real-time data for each single animal to feedback systems . In extensive sheep farming, there are several stationary tools such as AD, weighting crates or a walk over weight system. Although the systems are extensively tested and reached advanced stages of development, they are not yet accepted by dairy sheep farmers for widespread commercial use .An AD, in simple terms, is an automat system centred around a selective gate with the ability to distinguish and direct the passage of animals. Most of the AD systems are based on the recognition of animals’ EIDs as the selective criteria. In extensive sheep farm, ADs and EIDs could be used together not only for data collection and feeding control but also as a tool to reduce manual labour for the flock . Animal selection is one of the most labour intensive activities on the farm, especially in events such as sheering, parasite treatments and selection for sale.
Automatic drafters could also be coupled with weighting systems in order to measure the condition of a single sheep, directing lower weight animals towards supplemented feeding areas accordingly .Originally developed for grazing cattle, both systems were consequently adopted and modified of sheep farming as well. The WOW was tried in field conditions where it proved its efficiency, consequently expanding its use to sheep management . The system includes a one-way passage leading to a key stimulant which the animals are forced to pass through. The weighting platform is placed in this corridor, and it communicates with the animals’ EIDs on each passage. Data regarding each single sheep are stored and could be matched against similar passages in a single day creating a more reliable result. When used by itself, the WOW system helps to reduce labour with fewer personal needed for animal sorting activity while pairing it with AD systems can allow better control on supplementation feeding . This combination has been proven to be efficient in several studies as presented by a recent review by Rutter and by Gonzalez-Garcia et al. , making it a viable instrument for farm management. The WC on the other hand is used by actively separating single animal by operator closing doors in a passage corridor. This way, each animal is weighted standing still and isolated from others. In the WC, the RFID identification could be done both by handheld transponders or by fixed reading antennas,flower pots for sale consequentially allowing the analysation of data in real time. Commercial models are already available on the market . The collected data could be used for various purposes such as ensuring lambs are ready for sale or anthelmintic treatments. The last use is of particular importance considering the growing awareness to the amount of anthelmintic resistant parasites in grazing sheep and the health implications derived from it . For this purpose, coupling the WC with a self-dosing fluid dispenser is a currently viable option with commercial products already on the market such as Te Pari fluid dispenser .
Virtual fencing is an innovative method for extensive animal management that replaces physical barriers with electronically placed boundaries. Animals are prevented from passage by a system of visible and/or audible cues combined with electric stimulus. Although VF is not able to provide a full sealing of an area, its flexibility and potential applications has attracted a growing amount of researches as well as stimulating commercial development with products such as BoviGuard, NoFence and eShepherd™. The main advantage of such a system is not the complete exclusion of animals from certain areas, but rather the possibility VF provides to guide and move the animals according to pasture availability . However, VF cannot completely replace all fences, as the hermetic exclusion of animal is impossible without physical barrier. Therefore, due to security reasons and property rights , the external fences of the pasture remain necessary. By using visible and audio cues prior to the electric stimulus VF systems are aiming to condition the animals to understand the limits of their area. Although there is a variability among the individual animals in understanding these limits, as a group the herd maintains its position . There are several factors however, which limit the adoption of VF systems on commercial farms. The first is its cost, although the cost of the system was estimated in 200 000 £ for 100 animals in UK, its difference is not as big in comparison with traditional fencing costs in the same country . However, VF cannot completely replace traditional fencing and a combined use will be always needed . Another weakness is the lack of technological infrastructure in sheep farms ; this includes network coverage and IT-related skills and understanding. Without this, farmers may find it difficult to trust hi-tech systems .