Table 1.

Time of exposure to Mycoplasma bovis: positive bedding sand and probability of detection if infection resulted for 12 naïve dairy calves

Calf	Treatment group1	Died or euthanized	Age at death, d	Days after first exposure to mycoplasma2	Days on mycoplasma-positive sand3	Probability of detection if infected,4%
1	Control	Euthanized	25	0	0	NA
2	Control	Euthanized	17	0	0	NA
3	Control	Euthanized	113	0	0	99.8
4	Exposed	Euthanized	98	90	35	99.2
5	Exposed	Died	85	80	35	98.9
6	Control	Euthanized	107	0	0	99.8
7	Control	Euthanized	76	0	0	99.3
8	Exposed	Euthanized	76	74	25	99.3
9	Exposed	Euthanized	74	745	25	99.3
10	Exposed	Died	4	45	4	NA
11	Exposed	Euthanized	67	63	14	96.5
12	Control	Euthanized	65	0	0	96.5

¹Treatment group = exposed or control (not exposed) to mycoplasma-positive bedding.

²Days after first exposure to mycoplasma = Remaining days the calf lived following the first exposure to mycoplasma-positive bedding, the time during which the calf could have contracted mycoplasma infection.

³Days on mycoplasma-positive sand = Actual days the calf was bedded with mycoplasma-positive bedding; bedding was intermittently culture-positive.

⁴Probability of detection if infected = Probability that the calf would have been detected as mycoplasma-positive (by at least one positive test result) if they had become truly infected 4 wk postexposure. This is calculated for control as well as exposed calves to allow for the possibility that they may have somehow become exposed to mycoplasma at the same time that exposed group calves did by contamination between calf treatment groups despite precautions taken. This shows the probability that calves would have been detected with mycoplasma if indeed they became truly infected. NA = Not applicable because the calf did not live until at least 4 wk after exposure.

⁵Calves 9 and 10 arrived the day they were born and were immediately exposed to mycoplasma-positive bedding.