There were analysed 1,465 data on tick counts made in naturally infested 421 Gyr Zebu cattle sired by 38 bulls. Eight counts were performed in one side of each animal from May 1994 through February 1996. Traits analysed were counts of engorged females >4.5 mm (xU, larvae (x2), nymphs (x3), males (X4), and total females (x5). After transformed to yi=loge[Xi+l], data were analysed by the method of least squares, the effects of month, sex, age of the animal, coat density, coat colour and forage type in the pasture being considered as fixed, while sires, animals within sires, and error were considered as random. Average loge of the number of engorged females (yi) was 1.24±.04 or 3.5 ticks per animal. All the effects but sex were statistically significant (P<01). Highest average tick counts were observed in the fall 1994 and winter 1995, while the lowest figures were observed in summer. Older (>11 years), dark haired animals were the most susceptible. Heritability of the tick count (y'i) was estimated as h2=.266±.029.
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, , 339–342, 1998
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