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Metabolic and body temperature responses to environmental conditions across seasons in finishing steers
Two finishing trials were conducted utilizing 80 crossbred beef steers (in each) across two seasons (summer and winter; initial BW = 489 ± 20.4, 387 ± 15.9 kg, respectively) at the University of Nebraska-Lincoln Agricultural Research and Development Center near Mead, Neb. Continuous rumen temperature was collected throughout the duration of both trials. Blood samples were taken via jugular venous puncture every 2 weeks until 4 weeks prior to harvest for a total of 6 collections during the summer and 8 collections during the winter. Cattle in both trials were fed the same diet consisting of 51% HMC, 40% Sweet Bran, 5% wheat straw, and 4% supplement. Individual steer rumen temperature was used in the statistical model as a covariate. Only blood measures where rumen temperature was significant as a covariate were chosen to be reported. These selected blood measures were correlated to the 3-d prior average environmental temperature and the 3-d comprehensive climate index (CCI) relative to that blood collection day. Correlations between the change in blood measures and the respective change in rumen temperature, across collection points, were also analyzed. Additionally, environmental conditions were correlated to DMI and rumen temperature. Direct bilirubin, red blood cell count, hematocrit, and hemoglobin levels were all correlated (R > 0.22), during at least one season, to both the 3 d average environmental conditions and 3-d rumen temperature. Lactate dehydrogenase was negatively correlated (R < -0.62) to both 3-d averaged environmental conditions during the winter trial and also during the summer trial (R > -0.28). Red blood cell count was negatively correlated (R < -0.23) to 3-d environmental conditions during the winter trial however, was not correlated (R > -0.10) to environmental conditions during the summer trial. Rumen temperature was positively correlated to CCI and environmental temperature (R = 0.65, R = 0.63; respectively) during the summer. During the winter, rumen temperature was negatively correlated to CCI and environmental temperature (R = -0.27 and R = -0.19). Intake was negatively correlated to both CCI and environmental temperature (R = -0.32; R = -0.30) in the summer trial, however, during the winter trial DMI was positively correlated to CCI and environmental temperature (R = 0.22 and R = 0.24). Some blood metabolites change in accordance to environmental conditions and may be important during times of environmental stress. Additionally, environmental conditions affect both DMI and rumen temperature.
Keywords: body temperature, environmental stress, metabolites