An epidemiologic study of disease in 32 registered Holstein dairy herds inBritish Columbia

Data recorded in a herd health management system were obtained from 32 regi stered Holstein dairy herds from British Columbia. Frequencies of disease w ere described, and the effect of herd, age, year, season, and the interrela tionships between diseases within a lactation on the occurrence of disease were evaluated. Lactational incidence rates were computed for diseases with a short period of risk (ie, udder edema, milk fever, retained placenta, me tritis, displaced abomasum, and ketosis), whereas for diseases with a longe r period of risk (ie, cystic ovaries, mastitis and stable footrot), inciden ce densities were calculated. Overall, the disease incidence was low and sh owed an increase in frequency by year, which we attributed to more observin g and complete recording by the owner, rather than an actual increase in di sease incidence. Most diseases occurred early in lactation and their freque ncy increased with lactation number; the exception was udder edema, which o ccurred mainly during the first 2 lactations. An informal path model of disease interrelationships was made conditional o n herd. Based on the results we inferred 2 independent pathways: one starte d by udder edema, and the other by milk fever. Udder edema was directly ass ociated with mastitis occurrence from 0 to 30 d in lactation, metritis, and cystic ovaries. Mastitis from 0-30 d in lactation increased the risk of bo th mastitis from 31-150 d in lactation and cystic ovaries. Both of these in creased the risk of late lactation mastitis. Milk fever was directly relate d with displaced abomasum, which increased the risk of footrot. In general, diseases that occurred in early lactation tended to increase the risk of o ther diseases later in lactation.