GENETIC AND ENVIRONMENTAL FACTORS INFLUENCING THE RESISTANCE OF TERMINAL CROSS CALVES TO TICK Rhipicephalus (Boophilus) microplus AND HORN FLY Haematobia irritans

Abstract

One of the main problems affecting cattle production in tropical regions is infestation by ectoparasites, particularly the tick Rhipicephalus (Boophilus) microplus and the horn fly Haematobia irritans. The objective of this study was to evaluate the genetic and environmental factors that influence on the resistance of grazing calves against the tick R. microplus and the fly H. irritans. The study was carried out in Veracruz, Mexico. The ticks and flies counts were made from September 2007 to March 2008, in 27 eight month-old terminal cross calves. Data were analyzed through ANOVA, with the amount of ticks and flies as the dependent variables. Tick infestation was influenced by genotype (P < 0.05), period (months; P < 0.001), temperature (P < 0.001) and rainfall (P < 0.05), but not by sex and relative humidity (P > 0.05). Fly infestation was influenced (P < 0.001) by sex, genotype, period (months), temperature and rainfall, but not by relative humidity. In conclusion, the genetic and environmental factors did influence infestation by ticks and flies in growing calves.