Using an RFID device to obtain rumen temperature in cattle

Numerous behavioural and physiological parameters have been used to assess heat tolerance in cattle. Core body temperature is considered to be the best indicator of thermal load in animals but is difficult to obtain for long periods, i.e. weeks to months. Rumen temperature (TRUM) sensor boluses were administered to 18 steers (318.5±6.7kg). Six Brahman, 6 Angus and 6 Charolais steers were used in the study. The steers were held in un-shaded feedlot pens (2/breed/pen; 3 pens were used) over 130 days (Australian summer), and fed a 70% grain based diet. Rumen temperature was transmitted to a base station at 10-min intervals using transponder rumen boluses (RFID transmitter; Smartstock™, USA). The radio transmissions were converted from an analogue signal into a temperature value using proprietary software (TechTrol Inc., USA). In addition to rumen temperature, panting scores (0, no panting; 4, open mouth, tongue extended, drooling) were obtained daily for each animal at 2 h intervals between 0600 and 1800 h. These data (panting score and rumen temperature) were used to assess the heat load status of each animal. Heat susceptible animals were identified has having a panting scores >2 and a mean rumen temperature > 40.5 oC. The weather conditions over the duration of the study were sufficient to induce a heat stress response in the Angus on most days. Five heat wave events also occurred during the study. As expected the Brahman cattle were least affected by the climatic conditions and Angus the most affected (Figure 1). Rumen temperature was analysed by day (D; 0600-1800 h) and night (N; 1700-0500 h). The heat affected steers (Angus) had a higher TRUM (P<0.01) over the duration of the study; D means were 40.8±0.03 oC and N means were 40.7±0.03 oC; compared with 39.3 ± 0.03 oC (for both D and N) for the unaffected steers (Figure 2). During periods of high heat load TRUM of the non-heat tolerant Angus (affected steers) was greater (P<0.01) during the day (41.6±0.09 oC) and at night (41.0±0.03 oC). For the heat tolerant Angus steers (unaffected) the day time (39.7±0.03 oC) and nightime (39.4±0.03 oC) rumen temperatures were lower (P=0.01) than for the affected steers. As a reference for heat tolerance Brahman steers maintained a mean TRUM of 39.1±0.08 oC throughout the study (Figure 1). It would appear that TRUM may be a useful measure for identifying heat tolerant cattle both within and between breeds; however more work is required to fully establish the relationship. Further to this there is also a need to establish potential performance trade-offs between heat tolerant and non-tolerant animals withi a breed. Figure 1. Mean rumen temperature (oC) at hourly intervals (Time of Day) for unshaded Angus, Brahman and Charolais steers over 130 days (Australian summer). Figure 2. Mean hourly rumen temperature (°C) of un-shaded Angus (UNSH AA) steers and of heat tolerant steers (unaffected) and non-tolerant steers (affected).