Progestagen-induced oestrous response in Holstein cows and its influence on the sexual behaviour of non-treated pen mates

Grouped cows with oestrous cycles synchronised by the use of synthetic progestagen (SMB) appear to increase the degree of synchrony among them and this may enhance sexual behaviour in untreated herd mates. One hundred and twenty cycling cows were equally divided among three pens. For the first three days of the experiment, nine cows were induced to display oestrus on each of the three days. On the first day, one cow was programmed in pen 1, five in pen 2, and three in pen 3. The following day, the number of cows were three, one, and five, respectively, and on the third day, five, three, and one, in the respective pens. Nine other cows per pen were stimulated to show high levels of progesterone during the expected oestrus of the synchronised ones. The number of animals artificially induced into oestrus was directly related to the number of non-treated herd mates showing sexual behaviour (r = 0.96, P 0.05) in oestrous lengths, onset of oestrus, and sexual activity (mounts given and received) among treatments. Animals with exogenous high levels of P4 did not participate in sexual activities. It was concluded that a group of animals induced into oestrus by a synchronisation treatment may favour cycling herd mates to display concomitant oestrous behaviour.