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 2,500 or 5,000 Boophilus microplus larvae. Host resistance, the proportion of female ticks applied but not engorging was estimated from weekly counts of engorging female ticks of 4.5-8. 0mm long. Mean host resistance was 79 and 67% in two experiments. Host resistance was not significantly related to milk yield before infestation, to early pregnancy, or to parity. Culling the 10% 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 the existing low levels of resistance to B. microplus might be undertaken without compromising milk 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.

Evaluation of tickGARD(PLUS), a novel vaccine against Boophilus microplus, in lactating Holstein-Friesian cows

The effects of vaccination with the Bm 86 vaccine TickGARD(PLUS) against infestation with cattle tick (Boophilus microplus) and of holding cattle on a feedpad until 09:00 hours after the morning milking was tested on 40 mid lactation Holstein cattle using a factorial design. Vaccination resulted in a 56% reduction in tick numbers in the field over one generation, and a 72% reduction in laboratory measures of the reproductive efficiency of ticks. The liveweight gain of vaccinated cattle over 27 weeks was 18.6 kg higher than that of controls, and vaccinated cattle tended to have lower somatic cell count in milk (SCC). There were no other significant differences in measures of production. Cattle kept on the feedpad after the morning milking carried 26% more ticks than those returned immediately to their paddocks.