Parasitism is a primary cause of production losses in most cattle-producing countries of the world. Losses may
involve mortality, reduction in weight gain, low fertility,etc. (Perry and Randolph 1999). In raising livestock for food production, studies that help to quantify the economic losses caused by parasitism are important, especially in the
smallholder farming systems in developing countries (McDermott et al.1999). However, it is likely impossible
to give an accurate estimation of the economic importance of parasitic diseases because it varies greatly between
countries and regions, depending on climate, nutritional status, and the intensiveness of farming in the area. In most
countries, including Thailand, there is widespread occurrence of parasitic infections in domesticated animals, but
dramatic and obvious effects of clinical parasitism are less
often seen (Chompoochan et al.
1998
). The subclinical
effects disguising the adverse economic impact is a
problem of tremendous magnitude. As the parasites may
cause clinical and non-clinical diseases leading to econom-
ic losses, the goal of the veterinarians and producers is
prevention of parasitism through management, nutrition,
epidemiology and effective treatment.
Most of the work done on parasitic diseases in Thailand
has been conducted in dairy cattle (Chompoochan et al.
1998
; Padungtod et al.
2001
; Pholpark et al.
1999
). This
article reports the prevalence of helminths and protozoa as
well as factors associated with these infections in beef
cattle in the tropical livestock farming system of Nan
Province in the northern area of Thailand