AN EVALUATION OF THE USE OF SYNCHRONY TECHNOLOGY IN BEEF BREEDING HERDS

A model which was originally developed to derive the probability densi ty of a calving distribution for beef cotes under natural breeding has been modified to incorporate the effects of using oestrous synchroniz ation at the beginning of the breeding period. The model has been used to investigate five oestrous synchronization strategies over four her ds, each with differing calving patterns: no synchronization; every co w in the herd is synchronized; every anoestrous cow is synchronized; e very COW calving move than 20 days after the date of the planned start of calving is synchronized every cow calving 30 days after the date o f the planned start of calving is synchronized. Two of the herds previ ously had long calving periods and two previously had short, compact c alving periods. Model results showed that synchronization improved ave rage herd calf live weight by 21 kg in the two herds with long prior c alving periods but showed little effect in the two herds with compact prior calving periods. Synchronizing cows which calved move than 20 da ys after the start of calving in the herd showed similar results to sy nchronizing every cow in the herd and thus would be more cost effectiv e. Synchronizing cotes which calved move than 30 days after the start of calving in the herd showed a smaller advantage bur only in the herd s with long prior calving periods. The optimal strategy for oestrous s ynchronization in a herd will depend on the prior calving distribution and the average duration of anoestrus in that herd as well as the rel ative costs of the treatment.