Skin lesions and cattle hide damage from Haematobia irritans infestations

The horn fly Haematobia irritans L. (Diptera: Muscidae) has recently spread to Argentina and Uruguay and is believed to cause damage to cattle hides. Four groups of ten Holstein steers each were maintained for 58 weeks under different infestation levels with H. irritans to determine if it was the ca use of this problem. Hides (chrome tanned) from steers maintained under min imum infestation level had 4.7 +/- 3.8% of the area damaged. Maintaining th e steers under low H. irritans level for the last 44 days of the trial usin g insecticidal ear-tags, resulted in 29.5 +/- 15.8% of hide area being dama ged. Steers that were treated with 5% cypermethrin pour-on, when the H. irr itans population was close to 50 flies, showed that 31.3 +/- 16.6% of hide area was injured, and 46.6 +/- 12.8% of damaged hide area was found in hide s from non-treated steers. Significant differences were found between mean hide damage from steers maintained continuously under low H. irritans infes tation levels and all other groups. Hyperaemia was significantly lower in t he skin of steers under low H. irritans infestation level than in the skins of non-treated steers and steers maintained under low-level infestations f or the final 44 days. Eosinophil and mononuclear cell infiltration was sign ificantly lower when the population of H. irritans was less than six per st eer than when the population was more than 100 flies per steer. Low numbers of Stomoxys calcitrans were found in all groups, but most hide damage was presumed due to H. irritans.