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Research selection index categories

The research selection indexes that have been developed for industry review and feedback are grouped into three main categories, being Maternal, Maternal Plus and Terminal, with each category reflecting a different breeding system and objective, as outlined in Table 1

The Maternal and Maternal Plus selection index categories are designed for use in a self replacing breeding program where a portion of female progeny are retained as replacements. The Maternal and Maternal Plus categories are similar, with the difference being that the Maternal Plus selection indexes have an additional objective aiming to maintain mature weight, whereas the Maternal selection indexes do not include this component.

The inclusion of the additional mature weight objective in the Maternal Plus selection index category is a result of this category being modelled on a production system where the available pasture is fully utilised for the majority of the year. In this scenario, any increase in the maintenance requirements of the female breeding herd results in additional costs being incurred, and consequently an increase in mature weight is considered undesirable.

By comparison, the Maternal selection index category is modelled on a production system where the available pasture is not fully utilised for the majority of the year. In this scenario, any increase in the maintenance requirements of the female breeding herd results in minimal additional costs being incurred, and consequently an increase in mature weight is not considered undesirable.

The Terminal selection index category is designed for use in situations where Angus bulls are being used as a terminal sire over mature breeding females and all progeny, both male and female, are slaughtered.

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A description of each selection index, along with a decision support tree to assist with the identification of the selection index (or indexes) of relevance to a particular breeding program is included on the pages following.