Author
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Lefcourt, Alan |
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ADAMS, W - BROKEN BOW, NEBRASKA |
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Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/10/1996 Publication Date: N/A Citation: N/A Interpretive Summary: Heat stress is a common problem for cattle. Animals generally respond by reducing fed intake which, in turn, reduces growth rate. To monitor body temp. of feedlot steers during the summer months in Nebraska, temp. transmitters were implanted in ten, 10 month old, steers. Steers were fed at 630 and 1430 h using a finishing ration of 69 NEg Mcal with 13% protein and 4% roughage per d, and were housed in two open lots with stocking densities of 15.2 or 19.3 m2. Body temp., ambient temp., humidity, and wind speed were measured at 3 min intervals and mathematically filtered to produce 120 readings per d. Daily temp. means (39.04 C), maxima (39.89 C at 1836 h), minima (38.33 C at 823 h), and patterns were similar among steers. As peak daily ambient temp. increased, minimum body temp. decreased (.05 C per 10 F). After peak daily ambient temperatures reached a threshold of 78.1 F, maximum body temperatures increased linearly with peak ambient temp. (.35 C per 10 F). In addition, sharp peaks in body temp. were often seen in the late evening (around 2200 h) after ambient temp. had fallen to well below peak values. Peaks with amplitudes of .7 to 3.5 C and durations of about 1.5 h occurred in all animals on an average of 25 per cent of days. It may be that these peaks are an artifact of the mechanisms regulating body temp., e.g. the peaks could result from continuing attempts to moderate the effects of elevated ambient temp. even after ambient temperatures had begun to fall. The data from this study indicate that thermal regulatory mechanisms in steers respond not just to current ambient conditions, but represent an integrated response to daily temperature patterns, prior experiences, and expected future conditions. Technical Abstract: Heat stress is a common problem for cattle. Animals generally respond by reducing fed intake which, in turn, reduces growth rate. To monitor body temperatures of feedlot steers during the summer months in Nebraska, temperature transmitters were implanted in the peritoneum of 10 steers at 10 mo (325 kg). Animals were fed at 630 and 1430 h using a finishing ration of 69 NEg Mcal with 13% protein and 4% roughage per d, and were housed in two open lots with stocking densities of 15.2 or 19.3 m2. Body temperatures, ambient temperature, humidity, and wind speed were measured at 3 min intervals and mathematically filtered to produce 120 readings per d. Daily temperature means (39.04 +/- .12 C), maxima (39.89 +/- .21 C at 1836 +/- .73 h), minima (38.33 +/- .29 C at 823 +/- .38 h), and patterns were similar among steers. As peak daily ambient temperatures increased minimum body temperatures decreased (.05 C per 10 F; P <.01). After peak daily ambient temperatures reached a threshold of 78.1 F, maximum body temperatures increased linearly with peak ambient temperatures (.35 C per 10 F; P < .01). Sharp peaks in body temperature were often seen in the late evening (around 2200 h) after ambient temperature had fallen to well below peak values. Peaks with amplitudes of .7 to 3.5 C and durations of about 1.5 h occurred in all animals on an average of 25 per cent of days. Suggested is that these peaks are an artifact of the mechanisms regulating body temperature resulting from an over-compensation for the fall in ambient temperatures. Apparently, thermal regulatory mechanisms in steers respond not only to current ambient conditions, but also to prior experiences and expected future conditions. |
