Influence of Trypanosoma evansi infection on milk yield of dairy cattle innortheast Thailand

Effect of subclinical Trypanosoma evansi infection on the milk yield of new ly introduced Holstein Friesian dairy cattle were investigated. Five hundre d pregnant heifers were introduced in Loei Province, northeast Thailand and a total of 168 blood samples were collected at 20 farms during 6 visits ov er 2 years. Trypanosomes were found in cattle in June and November 1996, af ter which the parasite was rarely seen. On the other hand, the infection pr evalences by antigen-detection ELISA (Ag-ELISA) were around 40% from the fi rst sampling through October 1997; then, antigenemic cattle decreased to 20 % by June 1998. Milk yields of the cattle with detectable parasitaemia in J une and November 1996 were significantly lower than those of the non-infect ed cattle by Student's t-test. Similarly, the milk yields of Ag-ELISA posit ive cattle were lower than those of negative cattle at every sampling and s ignificant differences were observed during the first year and in February, 1998 (tested by 2-way ANOVA; T. evansi status and herd as factors). This s tudy suggested that subclinical trypanosomosis caused decrease in milk yiel d of newly introduced dairy. (C) 1999 Elsevier Science B.V. All rights rese rved.