Use only commercial tubes - use no bottle mixes to treat intramammary. This mastitis does not clear up with treatment and the cow does not show any signs of sickness. Drop in milk production. If you routinely cull the above type animals, mycoplasma will come and go and you will never know it. It won't spread if you do a good job of teat dipping and no bottle mixes are used.
Simple sample approaches Regular bulk tank analysis.
If records are kept of animals entering milking string, the animals since the last bulk tank sample can be sampled. This approach usually will take care of these problems. Full scale samples Expensive. Take great care in sampling - rubber gloves, sanitized between cows or you will spread from sample bottle to sample bottle, and think you have an epidemic when you only have a couple of cows infected. Epidemics usually happen by spreading from cow to cow using bottle mixes.