Effect of automatic backflushing on number of new intramammary infections, bacteria on teatcup liners, and milk iodine.

Effect of an automatic iodine (15 ppm) backflushing system on incidence of new intramammary infections, teatcup liner bacterial populations, and milk iodine was tested in a herd free of Streptococcus agalactiae and with a low prevalence of Staphylococcus aureus. In an 11-mo trial, backflushing was applied to teatcups that milked the right half of the udder; the left half served as control. Clawpieces were divided into left and right halves with each having a milk outlet. Postmilking teat dipping was discontinued. All lactating cows in the University herd were used, averaging 154 with normal attrition and additions of new individuals as they calved. Backflushing reduced numbers of staphylococci recovered from liners by 98.5% and Gram-negative bacteria by 99.5% as compared with unflushed liners. Backflushing significantly reduced new infections caused by Corynebacterium bovis. However, there was no effect on incidence of new infections by staphylococci, streptococci, or coliforms. Iodine concentrations averaged 243 micrograms per liter in milk from control quarters and 486 micrograms from backflushed udder halves. Interior surface cracking was more severe in backflushed teatcup liners than in control liners. These results do not justify the use of backflushing in a herd with low prevalence of contagious pathogens.