Effects and costs of a strategic selective treatment for controlling ecto - and hemoparasitosis in Holstein Friesian calves

Abstract

This work assessed the effectiveness and net operational costs of a strategic selective treatment for controlling ectoparasites (Rhipicephalus microplus, as well as Dermatobia hominis and Cochliomyia hominivorax larvae) and hemoparasites (Anaplasma marginale and Babesia spp.) in Holstein Friesian calves. Thirty calves were equally distributed in two groups: ST) strategic selective treatment and CT) conventional treatment. From birth, calves were monitored biweekly until 12 months of age. The CT group was subjected to parasite control according to directions provided by the veterinarian at the Experimental Farm of the Federal University of Lavras (FE/UFLA), whereas parasite control of the ST group followed criteria we had previously established. The ST group experienced fewer changes in physical traits on average and lower globular volume (GV) than the CT group (p < 0.05). Approximately 23% of ST calves exhibited external omphalitis, compared with 48% CT calves (p < 0.001). Additionally, ST calves were less affected than CT calves (p < 0.05) by R. microplus females and D. hominis larvae. Seropositivity rates from the indirect immunofluorescence reaction for A. marginale and B. bovis were similar for both groups (ST: 85.6% and 87.8%, respectively; CT: 83.2% and 83.2%). Additionally, subclinical (asymptomatic infection) anaplasmosis predominated in both groups during the dry period of the year. The daily average weight gains (DWG) were identical among ST (580 g) and CT (570 g), but the effective operational cost (EOC) was 3.7 times greater in ST (R$ 406.58/animal) compared with CT (R$ 110.90/animal). Laboratory exams to monitor the animals represented the largest share of the cost (82.7%) in ST, whereas drug expenses represented the highest costs (49.8%) in CT. Despite having a greater EOC, ST was more efficient at reducing parasite burdens than CT. Calves in the former group presented fewer R. microplus or D. hominis, and experienced a lower percentage of hemolytic anemia (VG < 24%). However, ST no affected the dynamic of A. marginale-and B. bovis-related infections, indicating that the FE/UFLA may be characterized as enzootically stable for these species. ResumoObjetivou-se avaliar a eficácia e os custos operacionais efetivos de um tratamento estratégico seletivo no controle de ecto (Rhipicephalus microplus e, larvas de Dermatobia hominis e Cochliomyia hominivorax) e hemoparasitos (Anaplasma marginale e Babesia spp.), em bezerras da raça holandesa, na Fazenda Experimental da Universidade Federal de Lavras (FE-UFLA), MG. Trinta bezerras foram distribuídas igualmente em dois grupos: TE) Tratamento estratégico seletivo e TC) Tratamento convencional. As bezerras foram monitoradas a cada 14 dias desde o nascimento até os 12 meses de idade. O controle de ecto e hemoparasitos, no TC, foi realizado de acordo com a orientação do médico veterinário responsável pela FE-UFLA. No TE, esse controle de parasitos seguiu critérios, previamente, estabelecidos pelos pesquisadores deste estudo. Nas análises estatísticas uti...