Management of premature lactation in dairy heifers

Summary

The occurrence of premature lactation is recognised as being a significant problem in dairy heifers exported from Australia by long-haul sea voyage, causing wastage ofexported animals predominantly due to devaluation or rejection of consigned animals as unfit for p​​urpose by importers.
The risk factors that lead to the occurrence of premature lactation are poorly understood. Although a substantial number of theories exist, the cause of the condition has not been elucidated and methods to control the incidence of the condition have not been established.
Following a critical review of the available literature and surveying of interested personnel with experience of the long-haul trans​portation of dairy cattle, exposure of exported dairy heifers to zearalenone in pelleted ship rations is considered to be a plausible explanation, at least in part, for the occurrence of premature lactation in such animals. It is also the factor most amenable to further investigation. There is sufficient evidence to suggest that zearalenone may commonly contaminate pelleted feedstuffs fed to dairy cattle before and/or during long-haul transport, and the link between exposure and premature lactation is also biologically plausible.
To further investigate this hypothesis we propose the following strategy: Determine whether zearalenone contamination of rations loaded onto ships used for long-haul export voyages from Australia does occur and, if so, to what extent; Evaluate and validate a simplified method for measuring zearalenone in feedstuffs that would be practical for on-board testing of livestock rations; Compile more reliable data to document the occurrence of premature lactation in exported heifers and the risk factors presumed to contribute to the syndrome; and Explore the potential for interactions between various risk factors using land-based feeding trials.​