Arteriovenous Anastomoses in the Dermal Vasculatureof the Skin of Bos taurus Cattle, and their Relationship with Resistance to the Tick, Boophilus micro plus

Abstract

Bos taurus cattle with high resistance to the tick Boophilus microplus, whether free-grazing or in covered pens, had significantly more arteriovenous anastomoses (AVA) in their skin than did animals of low resistance. These differences in number of AVA associated with resistance level were most marked above the level of the sebaceous gland in the neck region, an area favoured for tick feeding. In this skin layer, the number of AVA in low-resistance animals (4.0 plus or minus 0.4 per 2.1 mm) was significantly lower than in animals of high resistance (12.3 plus or minus 2.2 per 2.1 mm) while the mean value for the naive animals (8.2 plus or minus 1.0 per 2.1 mm) was intermediate. No differences in morphology of AVA were detectable between the three groups using light microscopy.