Cattle respiration rates in moderate and hot cyclic conditions

Abstract

Animal Production in Australia 1998 Vol. 22 CATTLE RESPIRATION RATES IN MODERATE AND HOT CYCLIC CONDITIONS J.B. GAUGHANA, G. HAHNB and A. PARKHURST A B C C Dept of Animal Production, The University of Queensland, Gatton College, Qld 4345 USDA-ARS Meat Animal Research Center (MARC), Clay Center, NE, USA 68933 Dept. of Biometry, University of Nebraska, Lincoln, NE, USA 6853 Respiration rate (RR) has long served as a gross indicator of heat load in animals during hot weather, increasing when animals need to maintain homeothermy by dissipating excessive heat as more benign avenues for heat loss become inadequate. Ambient temperature (ta) is of primary interest as it has a much greater influence on RR than humidity. The object of this study was to refine existing functional relationships between RR and ta and apply this information to the tactical management of cattle in hot weather. A 120 day study was undertaken at the MARC Environmental Laboratory at Clay Center, NE, using eight Bos taurus (Hereford x Angus x Simmental) steers growing from approximately 375 to 475 kg liveweight. The steers were housed in individual stalls in two environmentally controlled rooms (four stalls/room) and exposed to repeated cycles of thermoneutral (TNC; 18 � 7oC) for 12 days followed by nine day exposure to hot conditions (HOT; 32 � 7oC). Values for temperature humidity index, as described by Hahn et al. (1998), ranged from 52.5 to 70 for the TNC and 72.5 to 85 for HOT conditions. The cattle were fed a high concentrate diet ad lib. Exercise was provided weekly using a treadmill, at least 24 hours before RR observations. RR (obtained by observing each animals flank movement) were observed hourly on eight occasions for 24 hour periods (n=1536). The observations were made during the last few days of exposure to TNC (four periods) and HOT (three periods) and on one occasion on the second and third day of exposure to HOT. These observations provided the data for evaluating (i) a threshold for increased RR as a function of ta (ii) the rate of change in RR below and above the threshold ta, and (iii) time lags between the change ta and the resultant RR. The data were analysed using SAS (1993). Using data from all steers during exposure to TNC and HOT, the relationship between RR and ta was determined (Table 1). Further analysis indicated that the temperature threshold was 21.3oC, although for individuals the threshold varied from 17 to 23oC; the rate of increase in RR below 21.3oC was 1.2 breaths/oC, but it was about 4.1 breaths/oC at temperatures above the threshold. During HOT the highest correlation coefficients were for RR lagging ta by two hours. Table 1. Functional relationships of respiration rate (RR) to ambient temperatur e (t ) for a growing Bos taurus steers (375 to 475 kg) in a shaded environment Relationship RR = 31.6 + 0.28t + 0.061t Linear approximations: RR = 32.2 + 1.23t a 2 a t range C a o r 2 Threshold 21.3 Ao B C 11<ta>39 0.72 No Lag RR at a specific t RR = -25.4 + 4.07t RR = 31.0 + 1.22t A a a < 21.3 21.3 a 0.08 0.54 0.10 0.64 B based on the first derivative of Two hour lag RR two hours after a specific t RR = -32.0 + 4.32t a a a < 21.3 21.3 Ambient temperature above which RR increases markedly with increasing t . a the quadratic function RR is easily observed in the field and may be used as the primary indicator of thermal stress. The observations suggest that healthy cattle with RR 60 breaths/minute (bpm) are not thermally stressed, while cattle with RR 120 bpm may reflect excessive heat loads and this rate should be used as a threshold for closer monitoring. As RR reaches 160 bpm or higher, consideration should be given to emergency actions for reducing excessive heat load (eg wetting the animals). HAHN, G., MADER, T.L. and GAUGHAN, J.B. (1998). Anim. Prod. Aust. 22, 318. SAS. (1993). SAS/ETS Users Guide, Version 6, Second Edition (SAS Institute Inc: Cary, NC). 322