Descrição anatomohistológica da orelha de bovinos de corte na sensibilidade auditiva e bem-estar animal

Abstract

The knowledge about beef cattle hearing has an utmost importance within animal production systems. Thus, the aims were: to evaluate the behavior of taurine and zebu cattle exposed to three levels of sound frequencies; to compare the macroscopic and microscopic ear morphology of taurine with zebu as like to correlate the influence of hearing on animal welfare of both. For in vivo assay, 30 cows with ages between 2.5 and 4 years and belonging to two distinct genetic groups, taurine (Bos taurus taurus) and zebu (Bos taurus indicus) were used. To evaluate the animal behavior before the different sound frequencies, an etogram was performed evaluating the responses of animals to three distinct frequencies: 65Hz, 8kHz and 20kHz with 60 dB volume and simultaneously within each racial group. Alongside that, the pinna area and the interaural distance were measured. For microscopic anatomy analysis, three females of each racial group were used, being samples of tissues of the pinna in different regions, as well as of the external ear acoustic meatus. Qualitative data were estimated through exploratory multivariate analysis and for quantitative analysis of variance,and means compared by F test (P<0.05). It was observed that the zebu cattle were more reactive than the taurines when compared in relation to the acoustic stimuli. Taurine showed a smaller area of pinna (89.354 cm²) than zebuines (118.222 cm²). The interaural distance showed a significant difference (P<0.05) between the two racial groups where the taurine had distance of 26.222 cm and zebu 21.737 cm. The morphometry results obtained in relation to the means of the hair follicles and sweat glands per beef cattle pinna area showed significant difference (P<0.05) between both groups in almost all evaluated parts, except for the dorsal skin of the middle portion of the pinna. With regard to cartilage area, taurine has smaller areas at the top of pinna and in the outermost portion of the acoustic meatus than zebu. For acoustic meatus length measurement, no significant differences (P> 0.05) were observed between taurine and zebu. Zebu group had reacted more to the low and high sound frequencies, with the greatest discomfort appearing at high frequency. When the average frequencies were exposed, the two racial groups manifested similar behavior. In zebu, the larger pinna area and the smaller interaural distance may be associated with a better capture of sounds for this group. There is a difference in histological composition in relation to the number of hair follicles, sweat glands and cartilage area dimensions between the racial groups, which should be associated with the dimensions of the pinna structures and the need to protect the structures of the auricle and acoustic meatus.