To assess the effect of Boophilus microplus infestations on milk yield of 117 cows of three Holstein-Friesian (HF) x Guzera crossbred groups (Fu 5/8 HF and >15/16 HF) were randomlv allocated to two treatments during their whole lactation: infestation with tick larvae or spraying with acaricides. Burdens of B microplus in the infested groups were estimated in 21, 28 and 65 standard semi-engorged female ticks per animal per day, respectively, for the three genotypes in the above order. Treatment effects were not significant (P>0.34) in the F, and 5/8 HF, but in the >15/16 HF infestation reduced yield by' 26% from the mean of the sprayed group (2052 kg, P<0.04). The treatment x genotype interaction was statistically significant (P<0.02).

R. L Teodoro, A. M Lemos, F. E Madalena

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 27: Reproduction; fish breeding; genetics and the environment; genetics in agricultural systems; disease resistance; animal welf, , 177–180, 1998
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