BVDV and BHV-1 infections in dairy herds in northern and northeastern Thailand

Abstract

Bulk milk samples from 220 dairy herds were collected at 9 public milk collection centres in the northeastern and northern Thailand, and a subset of 11 herds was selected for individual testing. The samples were tested for presence of antibodies to BVDV and BHV-1 using an indirect ELISA. The results from the bulk milk testing demonstrated a moderate level of exposure to BVDV and BHV-1 (73% and 67%, respectively). However, the low proportion of herds with high BVDV antibody-levels (13%) and the low within-herd seroprevalence of BVDV and BHV-1 in the 11 herds (24% and 5%, respectively), particularly among the young stock (15% and 0%, respectively), demonstrated a low prevalence of active BVDV infection and a low rate of reactivation of latent BHV-1. The presence of a self-clearance process was also indicated by the results from the individual testing. Moreover, a surprisingly low prevalence of BVDV and BHV-1 antibody-positive herds at one of the milk centres was found. This centre was established 5-10 years before the others. Our impression is that this reflects the self-clearance process, where consecutive replacement of imported infected animals without further spread has resulted in a nearly total elimination of the infections. Based on our experiences and on these results we are convinced that this process can continue if there is awareness of herd biosecurity. This is especially important in the context of a future intensification of the dairy production.

Figure 1

Map of Thailand showing the location of the 9 public milk centres from which the bulk milk samples were collected. The prevalence of BVDV ad BHV-1 seropositive herds among the 220 herds in milk centres 1–7, milk centre 8 and milk centre 9, are shown within diamonds and squares, respectively.

Figure 2

Frequency distribution of bulk milk corrected optical density (COD) values from the BVDV antibody assay (a) with an inserted histogram showing the percentage of herds in each BVDV class derived from the CODs, for 220 dairy herds in Thailand. (b) The frequency distribution of bulk milk COD from the BHV-1 antibody assay.

Figure 3

Box plot showing the distribution of bulk milk corrected optical densitiy (COD) values for BVDV and BHV-1 from dairy herds in nine public milk centres in Thailand, 2000–2001. Boxes represent the first quartile (q₁), median and third quartile (q₃) of the COD values from each milk centre, and lower (L) and upper (U) limits are defined as: L = q₁ - 1.5 × IQR and U = q₃ + 1.5 × IQR, where IQR = q₃ - q₁.