TABLE 2:
Level of bovine respiratory syncytial virus (BRSV) antibodies in bulk tank milk (BTM) and individual milk samples from the lactating cows in 11 herds
| Herd no. | Cow (years) | No. of lactating animals | Per cent positive animals | BTM (PP) | Mean (PP) positive individuals | Anticipated time since infection* |
|---|---|---|---|---|---|---|
| 1 | 22.1 | 28 | 96 | 56 | 60 | <11 months |
| 2 | 58.1 | 50 | 100 | 110 | 72 | <1 year 5 months |
| 3 | 26.2 | 10 | 10 | 36 | 114 | (5 years 9 months, 6 years 11 months) |
| 4 | 27.7 | 18 | 56 | 52 | 86 | (3 years 5 months, 3 years 11 months) |
| 5 | 27.3 | 23 | 100 | 61 | 58 | <1 years 1 month |
| 6 | 22.0 | 21 | 100 | 73 | 78 | <6 months |
| 7 | 49.9 | 48 | 98 | 74 | 54 | <5 months |
| 8 | 33.0 | 29 | 100 | 83 | 81 | <9 months |
| 9 | 40.8 | 33 | 100 | 90 | 83 | (8, 11 months) |
| 10 | 21.8 | 15 | 100 | 106 | 110 | <10 months |
| 11 | 20.1 | 14 | 100 | 109 | 99 | <8 months |
The herds were selected based on a high increase in level of antibodies (PP) against BRSV in two consecutive BTM samplings prior to the sampling occasion shown
*The time since infection is based on analyses of antibodies in serum from the lactating cows and younger animals. The lower limit is defined by the age of the oldest animal negative for BRSV antibodies and the upper limit by the youngest positive animal. When all animals tested positive, the time since infection is indicated as less than the age of the youngest sampled animal
PP, per cent positivity