**1. Introduction**

164 Modern Telemetry

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In this chapter, the authors review recent developments in the use of biotelemetry in poultry production. The chapter begins with an overview of advancements in biotelemetry and outlines the types of equipment that are commercially available as well as those adapted and developed by researchers primarily for use in farm animals. The authors then highlight the significant milestones achieved by the scientific community in using biotelemetry towards a more holistic poultry production guided by birds' physiological responses to environmental stressors. In particular, the authors discuss efforts at the University of Georgia towards building the next generation closed-loop poultry environmental controller which responds directly and in real-time to physiological needs of the birds.

Biotelemetry is defined as the remote detection and measurement of physiological, bioelectrical, and behavioral variables to monitor function, activity, or condition of conscious unrestrained humans or animals. This encompasses a broad range of techniques of varying invasiveness including video monitoring, non-contact thermometry, radio tracking and the use of internally or externally mounted remote sampling systems (Morton et al., 2003). Biotelemetry is not a new concept and it was first introduced by Einthoven in 1903 when he measured the electrocardiogram using immersion electrodes remotely connected to a galvanometer via telephone lines (Cromwell et al., 1973, as cited in Hamrita et al., 1998). In later years, NASA played a big role in the advancement of biotelemetry by using it to transmit astronaut biomedical data such as heart rate and body temperature to earth. In (N. F. Güler & Übeyli, 2002), the authors provide a detailed history of early uses and developments of biotelemetry.

Biotelemetry consists of sensing the variable of interest from the animal using miniature sensors or transducers. These can be placed on the animal, ingested by the animal, or implanted inside the animal by means of injection or surgery. The output of the sensor or transducer is modulated to a form which can be transmitted wirelessly over a distance from the animal to a receiver using an embedded transmitter. The received signal is demodulated and the measured variable extracted through proper signal conditioning and calibration by the data acquisition system. Biotelemetry data has been transmitted through every medium including air, vacuum, water, and biologic tissue using a variety of modulating carriers such as electromagnetic waves (especially at radiofrequency- hence the name radiotelemetry), light, and ultrasound (N. F. Güler & Übeyli, 2002). By far the most common carriers of biotelemetry data are radio waves. Due to the proliferation of biotelemetry in recent years, the Federal

Advances in Management of Poultry Production Using Biotelemetry 167

convert it to the original signal being measured. Dedicated multichannel programmable receivers with computer interfacing capabilities are now commercially available. Some of these receivers could accommodate as many as 100 transmitters at different carrier frequencies. The data acquisition system turns the received signal into measurements of the variable being monitored based on the calibration information provided by the user. The data acquisition system is usually interfaced with a computer to provide a user-friendly interface which facilitates control of the measurements as well as storage of the collected data (Hamrita et al., 1997). In earlier stages of biotelemetry, researchers used data loggers mounted on animals (Hahn et al., 1990, Feddes & Deshazer, 1993, Harris et al., 2001, and Eigenberg et al., 2002, all as cited in Lowe et al., 2007) to record and store the collected data (Lowe et al., 2007). More recently, most systems use remote data transmission (Gedir, 2001, as cited in Lowe et al., 2007; Lacey et al., 2000a; Brown-Brandl et al., 2003; Silva et al., 2005). In some applications, researchers have mixed data logging in the implant as well as

Modulation methods used most in biotelemetry systems include frequency modulation (FM) where frequency of the carrier varies proportionally to the signal being transmitted; amplitude modulation (AM) where amplitude of the carrier varies proportionally to the signal; and pulse modulation where the carrier is a series of pulses. There are several types of pulse modulation techniques including pulse amplitude modulation (PAM) where the amplitude of the pulse varies proportionally, pulse width modulation (PWM) where the pulse width varies proportionally to the signal, and pulse-interval modulation (PIM) where the carrier signal is

Proper signal amplification within the transmitter unit is performed and, depending on the transmission media, may include a miniature "coil" or "whip" antenna for radio communications, an LED for infrared or visible light communications, or an ultrasonic transducer for acoustic communications. When multiple transmitters are used, each transmitter sends its output signal at a different carrier frequency so that outputs of different transmitters are not mixed. However, it is common to measure multiple variables within the same transmitter and have each variable modulate the carrier frequency differently. In the case of AM and FM modulation, this is called frequency multiplexing. In the case of pulse modulation, this is called time multiplexing (N. F. Güler & Übeyli, 2002). Using a light carrier has been shown to provide high bandwidth communication, and is

In biotelemetry systems, long operational life of the wireless sensor unit is an essential requirement. These systems have typically been powered using either batteries embedded inside the transmitter units or through external power sources. External powering of biotelemetry sensors includes RF power from a base unit and inductive powering based on magnetic coupling (Ko et al., 1977, de N. Donaldson & Perkins, 1983, Vanschuylenbergh & Puers, 1996, and Jeutter, 1983, all as cited in N. F. Güler & Übeyli, 2002). For sensor units powered using internal batteries, the size of the device often constrains both the operational life and the transmission range. For a given chemistry, there is a generally proportional relationship between battery size and energy storage capacity, so that smaller sized batteries have shorter useful lives in a given device. Concerning RF transmitters, the useable range often shrinks with the size of the transmitter due to decreased space for signal amplification circuitry and efficient antennae. In addition, the power consumption of the device tends to increase proportionally with the intended transmission range, the sensor sampling frequency, and the data transmission rate. To prolong the life of the battery in an implanted

turned on and off at a rate that is proportional to the variable being transmitted.

relatively more immunity from interference (Ackermann et al., 2006).

transmission to a data acquisition system (Lowe et al., 2007).

Communications Commission (FCC) has allocated dedicated frequency bands for biotelemetry use in the VHF range, generally over 100 MHz. Typically variables that have been monitored through biotelemetry fall in four categories: (1) Bioelectrical such as ECG, EMG, and EEG; (2) physiological such as blood pressure, blood flow, and temperature; (3) behavioral such as activity levels; and (4) chemical such as pH.

Through biotelemetry, it is possible to continuously monitor multiple physiological variables without handling or restraining the animal and attaching it to wires and probes. This reduces stress and physiological disturbance of animals by removing the influence of the measurement procedure and thereby improving the quality of data. This also allows for unattended operation reducing labor. Also, animals instrumented with implanted telemetry are free of infections that result from exteriorized catheters and lead wires (N. F. Güler & Übeyli, 2002). Biotelemetry provides the opportunity to increase the frequency of observation or continuously monitor multiple variables over extended periods of time therefore significantly increasing access to larger amounts of physiological data. Additionally, biotelemetry makes possible real-time processing of collected data and the ability to act on it. Knowing how key parameters are changing in real-time in animals allows, for instance, faster adjustment of feeding times to activity rhythms, more objective identification of the preference/tolerance margins towards environmental variables and precise assessment of the impact of environmental or operational changes (Baras & Lagardère, 1995). Lastly, biotelemetry reduces bias and observation influence, therefore contributing to more accurate measurements (Eigenberg et al., 2008). These characteristics of biotelemetry have improved a wide range of applications and enabled new possibilities that were previously unimaginable.

It is however worth mentioning that telemetry can cause suffering to animals in the short and long term if appropriate procedures and refinements are not implemented. In (Morton et al., 2003), the authors state that telemetry is often presented as a refinement, in that it can reduce or eliminate stress caused to animals but like all other procedures on animals, it also needs to be refined. They indicate that the impact of telemetry on animals in practice depends on whether or not surgery is used; the devices used; whether the technique restricts the subjects' abilities to express a range of desirable behaviors; and whether ways of refining both procedures and husbandry were fully researched. The authors provide a 40-page report detailing ways to refine both husbandry and procedures in telemetry applications to minimize suffering and improve welfare of animals. Similarly in (Hawkins et al., 2004), the authors detail husbandry refinements for telemetry procedures.
