Effect of caprine arthritis–encephalitis virus infection on milk cell count and N -acetyl- β –glucosaminidase activity in dairy goats

SUMMARY. Bacteriology, somatic cell counts (SCC) and jV-acetyl-/?-glucosaminidase(NAGase) activity determinations were conducted on milk samples collected fromdoes in three dairy herds with caprine arthritis—encephalitis virus (CAEV) infection.In two herds, CAEV-infected does were more likely to have a subclinical bacterialinfection of the udder than CAEV-free does (P < 0-05). Does with CAEV but nobacterial udder infection had significantly greater mean SCC and NAGase activitythan CAEV-free does without udder infection (P < 0-01). In two herds, changes inmilk SCC and NAGase associated with CAEV infection were similar to thoseproduced by coagulase-negative staphylococcal infections. The findings confirm thatindirect indicators of bacterial mastitis infection may have reduced specificity indairy goat herds with CAEV.Caprine arthritis-encephalitis virus (CAEV) is a lentivirus of goats in theretroviridae family which includes maedi-visna virus of sheep, equine infectiousanaemia virus, bovine immunodeficiency virus and human immunodeficiency virus.One common factor of these viruses is lifetime persistence of infection (Zink et al.1987).Although the prevalence and severity of clinical signs due to the virus varygreatly, CAEV is associated with disease syndromes including arthritis and chronicprogressive pneumonia in adult goats, and leucoencephalomyelitis in goat kids(Robinson & Ellis, 1986). The virus may also cause mastitis (Kennedy-Stoskop et al. f1985; Post et al. 1986; Lerondelle et al. 1989) and has been isolated from mammarygland tissue and milk of does seropositive for CAEV (Kennedy-Stoskop et al. 1985)f .It has been suggested that all CAEV-infected does have viral infection of themammary gland (Kennedy-Stoskopf et al. 1985) which is a target for the virus(Lerondelle et al. 1989). Colostrum and milk are the primary modes of transmissionof CAEV from one generation to the next and 100% infection of kids suckled byinfected does has been demonstrated (Adams et al. 1983).CAEV is prevalent at high levels in Australia (Campbell & Thomas, 1984; Surmanet al. 1987) and in many other countries (Adams et al. 1984). It is possible that thepresence of viral mastitis due to CAEV could interfere with detection of bacterialmastitis when indirect mastitis detection tests, in particular somatic cell count (SCC),are used. Does free from bacterial intramammary infections can produce milk withhigh SCC (Post et al. 1984). High cell counts have been attributed to the presence ofcytoplasmic masses originating from apocrine secretions (Dulin et al. 1983) and cell