Behavior of dairy calves after a low dose of bacterial endotoxin.

The aim of this experiment was to better describe early behavioral responses of calves to illness to help improve early detection. We examined the behavior of calves after injections of very low doses of bacterial lipopolysaccharide (LPS). Fifteen dairy calves of 2 ages (3 and 20 wk), housed in individual pens and fed milk and concentrates with free access to hay and water, were injected i.v. with 1 of 2 low doses (0.025 or 0.05 microg/kg of BW) of LPS before feed delivery with saline injections as a control using a crossover design. Fifteen calves showed an increased body temperature (>39.5 degrees C) lasting 2 to 8 h, with a maximum temperature of 40.59 +/- 0.52 degrees C attained 4.62 +/- 0.96 h after the LPS injection. Video recordings were used to measure durations of behaviors during a 4-h period when body temperatures were elevated. We found a decreased duration of rumination (LPS vs. saline 6.42 +/- 3.69 min vs. 24.57 +/- 6.64 min; P = 0.001) and hay eating (23.11 +/- 6.93 min vs. 31.52 +/- 7.54 min; P = 0.04), a decreased frequency of self-grooming (13.47 +/- 1.75 vs. 24.07 +/- 3.12; P = 0.008), and an increased duration of lying inactive (132.63 +/- 10.60 min vs. 104.39 +/- 12.63 min; P = 0.02). There was an increased bout frequency (P = 0.002) and mean bout duration (P = 0.005) of standing inactive. Changes in these behaviors may indicate the beginning of illness. Time spent lying down and amount of concentrate and milk consumed were not affected. There were no differences between the 2 doses and no interactions between LPS and the age of the calves. Very low doses of LPS seem promising to understand early development of sickness behaviors in dairy calves. However, the short duration of the effect and differences between calves in sensitivity to LPS must be considered as limitations to the effectiveness of this model.