Variability in vocal and behavioural responses to visual isolation betweenfull-sibling families of beef calves

In order to assess the value of vocal response as an indicator of welfare i n cattle, it is necessary to investigate factors which influence vocal beha viour of individuals, that are independent of the specific environmental co nditions to which they are exposed. The effect of parental differences, sex , age and weight on vocal responses of calves to visual isolation were exam ined. The relationship between vocal response and the amount of body moveme nt during isolation were also evaluated. Seventeen full-sibling families of beef calves (N = 130) were created by br eeding five sires with 13 superovulated dams. Embryos were transferred into unrelated cows, which reared the calves to weaning age. Vocal response of calves and body movement were measured on four occasions, while they were v isually isolated for 1 min on a single animal scale platform. The first two observations were made on the day of weaning (mean age 166 days) and the f ollowing day. At the third and fourth observations their average ages were 278 and 350 days, respectively. On the four occasions 33.3, 34.8, 27.8 and 38.6% of calves, respectively, vocalized. Both sire and family had a signif icant influence on the number of vocalizations and acoustic properties of t he sounds. Electronically-measured movement while on the scale was also inf luenced by sire and family, but there was no relationship between vocal res ponses and body movement. There was a tendency (P = 0.08) for older and the refore heavier calves to produce longer vocalizations. In the final observi ng session, age and weight were positively correlated with fundamental freq uency and the sound pressure level at the frequency of greatest intensity, and negatively correlated with the loudest harmonic. At the last two observ ations, significantly more heifer calves than bull calves vocalized. There was little difference between the acoustic properties of heifers' and bulls ' vocalizations. The considerable individual variability in vocal response within a group of identically-treated calves is partly due to parental genetic influences th at an independent of rearing and early experience. Other endogenous charact eristics such as sex, age and weight also influence vocal response. But the re is: no clear relationship between individual temperament (as assessed by the amount of body movement during isolation) and characteristics of vocal response. (C) 2001 Elsevier Science B.V. All rights reserved.