Breeder mortality: Determining property-level rates in northern Australia

Summary

At the time of this report, there was no reliable information about on-property levels of breeder cow mortality in extensive areas of northern Australia. This is a consequence of incomplete or inaccurate property herd records and the extensive nature of the properties, which makes a count of all deaths impossible. These deaths represent a loss in income and, above certain levels, these losses may be reduced by implementing proven strategies. 
The aim of this project was to determine breeder cow death rates on properties in northern Australia on a regional basis, speculate on causal factors, and develop a method of determining death rates over time at a property and regional level.  The project team worked with 45 properties over nine regions and was able to extract useful information from 36 of these properties to produce data that covered periods varying from three to nine years. The regions included in the analysis were: 
1. Queensland southern Gulf 
 2. Queensland northern Gulf 
3. Northern Territory Barkly Tableland 
4. NT Gulf/Katherine/Sturt Plateau 
5. NT Alice Springs 
6. NT Victoria River district
7. Kimberley East 8. Kimberley West 
9. Pilbara. From a list of all properties in each region, properties were randomly selected and, if they met certain selection criteria such as herd size, these properties were contacted to confirm they met all the selection criteria and were willing to cooperate. 
The data were mostly collected during property visits, using a pre-determined template of questions which would allow the data and management practices described to be analysed to determine associations between management practices, rainfall, climatic events and rates of female and male mortality. During property visits, the team members were able to interrogate management on the validity of the data, seasonal conditions, land types and property management practices. 
The literature review highlights the difficulties in sourcing accurate data to describe mortality in breeding cows on northern beef properties and the use of a variety of alternative and indirect measures to estimate breeder mortality. The review describes approaches used to estimate breeder mortality and provides estimates from properties and regions across much of northern Australia. Major factors influencing breeder mortality are identified along with management strategies for minimising their potential to adversely impact upon breeder deaths. 
There is a small number of more detailed studies that have collected data on breeder mortality from observations conducted on northern beef properties. A number of studies have collected retrospective property records or have used surveys to collect producer estimates of breeder mortality rates. A number of reports have used indirect methods based on sales data in combination with estimates of breeding populations to estimate mortality rates in breeders. Other studies have used herd modelling software generally in combination with records either from producers or from other sources (sales, abattoir or animal movement records) to generate estimates of mortalities in breeders. 
There is considerable variability in estimated breeder mortality rates between properties and regions within northern Australia. There are undoubtedly individual properties where the combination of environmental, animal and management factors are able to produce relatively low breeder mortality rates (under 3%). Across much of northern Australia, the literature reviewed in this report from the last two decades suggest that typical annual breeder mortality rates are likely to be between 2 and 12% per annum with higher mortality rates expected in cows aged 10 years or older (15 to 20% or higher) and in severe drought conditions (>20%). 
There is relatively little available information to characterise the causes of breeder mortality in detail. The major combination of conditions likely to increase mortality risk is poorly conditioned cows that are heavily pregnant or in early lactation during the late dry to early wet seasons. There is an age associated increase in mortality risk that is likely to occur in cows older than 8-10 years, though this is expected to vary between animals and properties, and individual cows that are able to maintain good dentition and body condition may be able to remain productive past 10 years of age. 
Where breeder mortality is high there is strong evidence to suggest that strategic investment should be directed at reducing breeder mortality before attempting to improve other performance measures such as weaning rates. Where breeder mortality is relatively low it may not be useful to direct further investment into reduction of mortality. A range of management factors is discussed that have the potential to reduce breeder mortality. It is recognised that breeder mortality is only one of many performance measures that can be used to assess enterprise performance and guide strategic decisions. Further effort is recommended to better characterise breeder mortality and to incorporate consideration of breeder mortality into benchmarking and strategic management options for producers in the future.