Remote sensor collars measure age at puberty in tropical beef heifers in northern Australia

A total of 173 heifers were fitted with SenseHub™ collars and recorded for their activity and rumination behaviour over a 530-day period. Daily averages and their change over time were plotted in a heat map for each heifer. Patterns in the plots were assessed by five scorers independently to determine the date of each heifer's first oestrus event. Her age was referred to as collar-determined age at puberty (CollarAP). Heifers were also regularly ultrasound ovarian scanned to determine age at first observed corpus luteum (AGECL), this was used to assess the relationship with CollarAP. The results from this study show the collars can accrue large amounts of data but interpretation was not simple and differences existed between the five scorers. However, mean CollarAP and AGECL were the same and correlations were positive and strong, ranging from 0.69-0.83 across scorers. When observations on CollarAP were pooled across scorers, the correlation with AGECL was 0.86. Further, least squares means for sires for the two traits were also highly related (R2 =0.89). This study has shown the collar data can be used to determine age at puberty in tropical beef heifers.