How significant a risk are carrier cows for maintaining infection in a herd?
Cows are potential sources of new infections and maintaining the organism in a herd. Usually they only harbor the organism for a few heat cycles after infection or pregnancy loss. Some cows can carry the organism through the gestation period and well into the postpartum period. Skirrow found two of 40 infected cows from two herds that carried the infection through the entire gestation and for up to nine weeks postpartum (Skirrow SZ. 1987. Identification of Trichomonad-Carrier Cows. JAVMA. 191:553-554). Such a ‘carrier cow’ presents a problem when trying to control the disease and offers at least partial explanation for the persistence of infected animals when control measures have concentrated on eliminating positive bulls. True prevalence of carrier cows is unknown, but is thought to be less than one (1) percent. These cows may be clinically affected (abortion, infertility, pyometra) or there may be no apparent clinical signs.
