Characteristics of oestrus measured using visual observation and radiotelemetry

The aim of this study was to measure the level of agreement between characteristics of oestrus measured using visual observation and radiotelemetry. Oestrous cycles in 20 non-lactating Holstein cows were synchronised by treatment with an intravaginal progesterone releasing inserts and injections of oestradiol benzoate for a first oestrus (Round 1) and then re-synchronised for two subsequent and successive oestrous cycles (Rounds 2 and 3). Cows were ovariectomised following the third synchronised oestrus and then retreated to induce oestrus (Round 4). Oestrus was monitored by continuous visual observation and radiotelemetry between 24 and at least 60 h after removal of inserts at Rounds 1–4. Significant differences (P<0.001) were obtained between the mean number of mounts (42.7 versus 17.8), duration of oestrus (14.4 h versus 10.9 h), total duration of mounts (223.9 s versus 33.1 s), mean duration per mount (5.6 s versus 1.9 s), the number of mounts per hour (3.5 versus 2.0) and the interval to oestrus (41.2 h versus 42.8 h) between values determined by visual observation compared with radiotelemetry, respectively. The 95% limits of agreement for all the characteristics of oestrus measured were wide although the efficiency of detection of oestrus for both methods of recording oestrus were high (97.5% (78/80) versus 93.8% (75/80), for visual observation and radiotelemetry, respectively; P=0.25). We conclude that there is poor agreement between characteristics of oestrus measured with visual observation and radiotelemetry in Holstein cows following monitoring of synchronised oestrous cycles, although both methods were equally efficient for the detection of oestrus.