Figure 1. Mean somatic cell counts in treated quarters before and after Nolvasan® Infusion.
Milk yield decreased from 36 lb/day pretreatment to a mean of 24 lb/day over the remainder of lactation (Figure 4), which is not excessive given the loss of one quarter and the normal decrease that is associated with advancing lactation. Antimicrobial residues resulting from Nolvasan® infusion were detected for up to 35 days in a few quarters, but most quarters from which secretions could be obtained were residue-free by 21 days. Residues were not detected in uninfused quarters of the same udder.
Figure 2. Somatic cell counts by day in uninfused and infused quarters.
Figure 3. Somatic cell counts in uninfused, uninfected quarters that were adjacent to treated quarters before and after Nolvasan® infusion.
Histological examination of infused quarters revealed that milk-producing tissues had involuted and appeared similar to “blind” or nonfunctional quarters, exhibiting significant reductions in milk synthesizing tissues. Six cows completed a nonlactating period and calved; all of the Nolvasan®-infused quarters remained nonfunctional in this subsequent lactation.
Figure 4. Average daily milk yield in treated cows before and after infusion.
Results suggest that a chronically infected quarter that does not respond to antimicrobial therapy can be rendered nonfunctional without damage to adjacent quarters. This procedure prevents abnormal secretion from being comingled with herd milk and elevating SCC and bacteria counts. In addition, such quarters no longer constitute a herd reservoir for mastitis-causing organisms, which can spread to uninfected cows. This method also allows the salvage of genetically superior animals for breeding stock. It is imperative to remember, however, that this procedure involves extra-label drug use and should be performed within the context of a valid veterinary/client patient relationship. Moreover, treated quarters must be identified in a manner to insure that they are not milked into the tank to avoid the presence of drug residues in herd milk.