Resistance of Holstein-Friesian cows to infestation by the cattle tick (Boophilus microplus)

In two experiments, the milk production of 59 Holstein-Friesian cows in mid lactation was measured over 1 week before artificial infestation with 2.50 0 or 5,000 Boophilus microplus larvae. Host resistance, the proportion of f emale ticks applied but not engorging was estimated from weekly counts of e ngorging female ticks of 4.5-8.0 mm long. Mean host resistance was 79 and 6 7% in two experiments. Host resistance was not significantly related to mil k yield before infestation, to early pregnancy, or to parity. Culling the 1 0% of cattle with the least resistance to ticks would result in removal of 19-21% of ticks in a herd. The results suggest that selection to improve th e existing low levels of resistance to B, microplus might be undertaken wit hout compromising milli production. However, low levels of resistance among the cattle studied and difficulties in assessment of resistance are likely to limit the usefulness of selection within the Holstein-Friesian breed. ( C) 2000 Elsevier Science B.V. All rights reserved.