Herd prevalence and incidence of Streptococcus agalactiae in Prince Edward Island and evaluation of the effectiveness of an eradication extension program

The first two objectives of the study were to establish the herd prevalence and incidence of Streptococcus agalactiae mastitis in the Prince Edward Island (P.E.I.) dairy industry. The third and fourth goals were to quantify the effectiveness of an intensive "on farm" and a less intensive "mail out" extension protocol. An attempt was also made to identify the management procedures which affected herd level eradication of S. agalactiae.

The herd prevalence and incidence of mastitis caused by S. agalactiae were determined during December, 1992 and June, 1994. At each census, bulk tank milk samples from all dairy herds (n = 452) in P.E.I. were tested on two separate occasions.

Herd level infection with S. agalactiae was associated with milk quality penalties and elevated bulk tank somatic cell count, a surrogate measure of production loss. Evaluation of the previously negative herds (December, 1992) in June, 1994 yielded an estimate of the incidence of 3.51 new herd infections per 100 herds per year.

Herds in the "on farm" program were 4.62 times more likely to eradicate S. agalactiae than the positive control herds. Path analysis, using information generated from a survey of study herds, revealed that, in general, herds that eradicated S. agalactiae did so by following a particular pathway which included participation in the extension program, consultation with udder health professionals, and whole herd milk cultures. The effectiveness of the "mail out" extension effort was not statistically different than the "on farm" program. However, because of the small number of herds in each group, the study had limited power to discern a difference, if, in fact, there was one. (Abstract shortened by UMI.).