Angus NZ

Indexes

The following three graphs reflects the relative change if the New Zealand Angus Published Sires (at the Mid-August 2020 TransTasman Angus Cattle Evaluation) were ranked on this selection index and the top 10% were used within a breeding program. Given that the Published Sires are the sires of the next generation(s) of New Zealand Angus cattle and have more highly accurate EBVs (due to having progeny) than the average animal in the database, these graphs represent the approximate selection response one would expect to see in the breed from using this index.

Self Replacing Index (SRI)

Above the 0 line (X axis) selects for more positive numbers and below the line selects for more negative numbers.
For some traits (e.g. growth), a positive response is desirable and for others (e.g. days to calving), a negative response is desirable.

Genetic Selection of bulls using only the SRI tool will on average over time develop a cow herd with the following:

  • Improved weaning rate through increased fertility and easier calving
  • A slowly decreasing cow size, milk and slowly increasing body condition
  • Progeny will be prime at a younger age for slaughter

These characteristics are ideal for an environment where the herd is exposed to prolonged seasonal feed deficits
and feeding supplement is unlikely.

Angus Pure Index (API)

Above the 0 line (X axis) selects for more positive numbers and below the line selects for more negative numbers.
For some traits (e.g. growth), a positive response is desirable and for others (e.g. days to calving), a negative response is desirable.

Genetic Selection of bulls using only the API tool will on average over time develop a cow herd with the following:

  • Improved weaning rate through increased fertility and easier calving
  • A slowly increasing cow weight/size, and milk production
  • Progeny will be prime at heavy carcase weights where the improved marbling and subsequent eating quality traits can be expressed.

These characteristics are ideal for an environment where the cow herd can be managed with extra feed if seasonal feed deficits occur.

Checking individual EBV’s relevant to your herd is advised.

Comparison of SRI and API

SRI is a maternal trait emphasised index. API is also a maternal driven index with added carcase trait emphasis.

API selected animals can produce more net profit per animal through extra performance when feed is abundant.
Finished progeny can be taken to heavier weights with increased likelihood of achieving marbling premiums.

SRI selected animals can produce more net profit per animal through extra performance in environments where
the cow herd is likely to be challenged by regular seasonal feed deficits, maintaining body condition is critical
to longevity and feeding out is not a viable option.

Checking individual bull EBVs to make sure the index and the EBVs match your expectations are advised.
Using the flow chart may help you with your decisions.

HDT Index (heifer/dairy terminal)

Above the 0 line (X axis) selects for more positive numbers and below the line selects for more negative numbers.
For some traits (e.g. growth), a positive response is desirable and for others (e.g. days to calving), a negative response is desirable.

This index is primarily driven by getting live calves on the ground, and producing an early maturing prime animal with added carcase traits for improved carcase yield and marbling with no direct selection for maternal traits.

NB. It is important point to be aware that while no emphasis has been placed on some traits,
for example maternal traits in the HDT, they still may be selected for indirectly through positive
or negative correlations with other traits, as is the case with Days to Calving in the HDT.

Purpose of Bull Purchase Flowchart

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How to choose the appropriate bull – fit for purpose?

The very first step before you start choosing a bull is to identify a breeding programme that does what you want it to and produces a product suitable for your farming system. Make contact with the bull breeder and take the time to visit the stud prior to sale day. Have a list of questions you want to ask your breeder. Beef + Lamb NZ Genetics have a guide for this. Decisions made on sale day can impact your cow herd for the next 16 years through their own progeny and the next generation (Daughters progeny).

Once you have chosen your breeder(s), have a look at the different BreedObject indexes.

BreedObject is a tool for formalising breeding objectives and $Indexes that can help you breed more profitable cattle. It uses TACE EBVs. It helps you target the type of commercial herd performance you need from animals for a given market production system, and it helps you identify seedstock that will be best suited to this. BreedObject $Indexes are intended for use by both stud and commercial beef producers.

BreedObject draws together the TACE estimated breeding value (EBV) figures on bulls into a single EBV, the $Index, which describes how well bulls suit a particular purpose. If you are interested in more than one type of commercial production purpose, you will be interested in more than one $Index.

Selection Indexes provide commercial beef farmers with a way of sorting animals into the most profitable for a particular breeding objective. They are multi trait based and so individual animals can be rewarded across a range of traits and therefore receive a higher $ value.

Once you have chosen the appropriate index for your production system, you then need to rank the animals on their index to create a shortlist.

The next step is to go through the shortlist and eliminate any bulls whose individual EBVs are not fit for purpose. For example, poor calving ease/high birth weight for heifer bulls or a level of milk that is inappropriate for your production system.

Now you have a target list and are prepared for sale day and all you need to do is work through your list and focus on the visible traits such as structure and docility. This will then allow you to do a final re-ranking of the shortlisted bulls and a final game plan for purchasing your bull. It is highly recommended that you stick to your list you prepared to make the best genetic decisions for your herd.

Frequently Asked Questions

What are the added features of version 6 over previous editions?

  Improved modelling of cow feed costs over the seasons

  Improved modelling of young animal growth

  Improved modelling of carcase, market specifications and values

What are the main objectives the SRI?

Increased emphasis on fertility, reduced emphasis on calving ease, reduced emphasis on late growth and more emphasis on early growth and a decrease in mature cow for efficiency.

What are the main objectives of the API?

Increased emphasis on fertility, reduced emphasis on calving ease, emphasis on later growth to allow IMF to be expressed. As a consequence, mature cow weight still slowly increases (less than previously). An increase in carcase yield is also emphasised. IMF trait emphasis hasn’t increased, but the economic value of a marbling premium has increased.

Why has the emphasis on the milk EBV decreased in the SRI?

Milk is a nutritionally expensive trait and therefore the optimum emphasis on the Milk EBV is dependent upon the production system and the environment in which the cows are run. Selection for increased milk production may be warranted when cows are run under good nutritional conditions, while poorer environments (e.g. hill country with no possible supplementation) may not support cows with higher Milk EBVs. In addition, high milking cows may not get
back in calf as easily as lower milking cows in the following year.

The response graphs show that the response for Rib and Rump Fats in the SRI is neutral and negative for the API. Will this adversely affect the cow body condition score particularly for cows running on harder country?

Rib Fat, Rump Fat and Cow Body Condition Score (BCS) all actually have positive emphasis applied in the indexes (Cow BCS has a 7% positive emphasis in the SRI and 4% in the API – more detail on the Profit Drivers and EBV weightings of each index can be found in the Interpreting NZAA Selection Indexes tipsheet on the TACE website). The reasons why this does not translate into positive Rib and Rump Fat emphasis in the selection response graphs is twofold.

Firstly, Rib and Rump Fat are different traits to Cow BCS with Rib and Rump Fat being a reflection of maturity in growing animals. In contrast, Cow BCS at mating is a reflection of how a cow can forage and subsequently manage her body energy reserves under strong competition for resources from functions such as pregnancy, lactation and fertility. These differences in body functions at different points in an animal’s lifetime mean that Rib and Rump Fat are not perfectly correlated with Cow BCS and in fact the relationship is such that Cow BCS can be improved independent of Rib and Rump Fat in the progeny. For example, in the profit drivers of the SRI index, progeny fat depth has a 1% emphasis whereas Cow BCS has a 7% emphasis which reflects their differing roles in the lifetime of beef cattle.

Additionally, fat is more nutritionally expensive than lean tissue and meat companies are reporting more cattle that exceed fat specifications than those being under minimum specifications. This places significant downward pressure on the Rib and Rump Fat EBVs in the index.

Secondly, the response graphs are generated from the Mid August TACE analysis results for the New Zealand Angus Association published sires. The published sires are used for the production of these graphs because the accuracy of their EBV’s are higher due to the presence of progeny and these bulls will be siring a significant proportion of the next generation(s). The downside of using the published sires list is that they are a sub population of the breed that has been selected on criteria other than the new indexes and thus the anticipated response observed in the graphs may not be perfectly representative of what one would expect to see in the breed in the future. The same graph generated from past TACE analyses had a slight positive selection response for Rib and Rump Fat from selection using the SRI.

Why have you added an HDT index and what will that achieve? Been there. Done that!

We do not expect stud breeders to use this index and would not recommend it for this purpose.

This index has been developed for a couple of reasons.

The dairy industry has approximately 4 times as many breeding females as the beef industry. The approach to bobby calves is changing due to social pressure and more calves will be reared for slaughter in the long term. It therefore makes sense that we try and add value to this product by providing appropriate genetics for the dairy farmer to source, the meat processor to market and the consumer to enjoy. Dairy farmers are very familiar with using indexes and this one is ideal for them whether it be for the purpose of cow or heifer mating.

This index is suitable for use over cattle of all breeds (beef or dairy) and ages where calving ease is an issue. For example, some commercial beef farmers do not like to retain females from their heifers and purchase a specialist heifer mating bull with all progeny slaughtered. This index is also appropriate for such a policy.

Can we compare the old index $ values with the new ones?

No you can not compare the values. Individual bulls are likely to re-rank as a result of the new indexes. We are using a new version of BreedObject with a lot more data used in the model, the re-ranking with this update may be more dramatic than normal. For these reasons comparing old index values with the new is not comparing apples with apples.

Why is the SRI model killing cattle at such a young age and low weight, is this realistic?

The SRI index is focused on efficient beef production under hard hill country conditions. To maximise efficiency, having animals finished before the onset of the second winter was a priority and the subsequent earlier emphasis on growth allowed us to increase the downward pressure on Mature Cow Size which further aided efficiency. While killing steers at such a young age may be optimistic for some commercial producers, indexes are a tool for the breeding of future animals and thus setting futuristic breeding goals is crucial.

Interpreting NZAA Selection Indexes – TACE

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Updated: 03/09/2020