Risk factors related to resistance to Rhipicephalus (Boophilus) microplus and weight gain of heifers

Abstract

The aim of the present study was to evaluate the influence of age and genetics in dairy heifers on resistance to the cattle tick Rhipicephalus (Boophilus) microplus and correlate these parameters with weight gain. Twenty-two heifers were evaluated from birth up to two years of age. Resistance to the cattle tick was evaluated by counting the number of engorged female ticks and subjective qualification of the larvae and nymph infestation. The animals were weighted in the first 24 hours after birth and at six, 12, 18 and 24 months of age. The average tick count and weight gain were compared by Tukey's test at 5% significance. Subsequently, linear regression was performed to verify the strength of the association between the risk factors age and genetics and infestation by R. ResumoO objetivo do estudo foi conhecer a influência da idade e da genética sobre a resistência ao carrapato Rhipicephalus (Boophilus) microplus e correlacionar estes parâmetros com ganho de peso de bezerras de origem leiteira. Foram avaliadas 22 bezerras desde o nascimento até dois anos de idade. A avaliação da resistência foi realizada por meio da contagem de teleóginas ingurgitados e qualificação subjetiva da infestação por larvas e ninfas. Os animais foram pesados nas primeiras 24 horas pós-nascimento, aos seis, 12, 18 e 24 meses de idade. A comparação das médias das contagens de carrapatos e ganho de peso foi realizada pelo teste Tukey a 5% de significância. Posteriormente foi realizada regressão linear para verificar a força da associação entre os fatores de risco idade e genética e a infestação por R. (B.)

South Indian zebu dwarf cattle show higher natural resistance to tick infestation compared to crossbreds: preliminary observations

“…The animals were grouped into four categories (no infestation, low, intermediate, and high infestation) based on the tick infestation level and subjective qualification of the larvae and nymph infestation (Da Silva et al 2015). Since the genetic background of the animals could influence the natural resistance against tick infestation, the breeds/genetic group was considered the genetic factor in the present study.…”

“…Furthermore, there are within-and between-breed variations in host resistance and purebred zebu is resistant to tick infestation (Kelley 1932). Several studies have suggested that Bos indicus (B. indicus) breeds and their crosses are more resistant than taurine breeds (Utech and Wharton 1982;Jonsson et al 2008;Ibelli et al 2012;Da Silva et al 2015;Lew-Tabor et al 2017). Factors like age, pregnancy, lactation status, sex, season, temperature, and humidity, as well as skin parameters like skin thickness, hair length, and coat score influence host resistance against ticks in cattle ( Utech et al 1978;Utech and Wharton 1982;Verissimo et al 1997Verissimo et al , 2002Jonsson et al 2000;Hughes and Randolph 2001;Webb and David 2002;Foster et al 2007;Gasparin et al 2007;Silva et al 2010;Ibelli et al 2012;Singh and Rath, 2013;Da Silva et al 2014, 2015.…”