COURTESY OF SHEEP GENETICS

Sheep Genetics have developed a range of selection indexes as tools to drive genetic improvement that considers multiple traits of economic or functional importance. Each index has been built to align with typical breeding objectives of various types of producers, aiming to improve profitability in commercial sheep enterprises.

When indexes are developed, Sheep Genetics define a breeding objective for different breeding scenarios. This involves an analysis of commercial flock production data to calculate the economic value of improving traits which affect profit, based on flock structure, production and price data. The breeding objective is then converted to an index by linking the profit traits to ASBV traits through genetic correlations.

Often the profit and ASBV traits are the same, for example weaning and post weaning weights (early growth rates) are key profit drivers in commercial flocks and are easy to measure in ram breeding flocks. Profit traits that are hard to measure rely on other correlated traits to drive improvement, for example using muscle and fat ASBVs to improve the profit trait carcase yield.

By combining the economic values of traits with the genetic relationships between traits, we can determine the appropriate relative weights which allow us to combine ASBVs into a single value for each animal.

Intramuscular fat (IMF) is a measure of the chemical fat percentage in the loin muscle of a lamb, and the visible component is known as marbling. IMF has been shown to have a large effect on the lamb eating experience, including flavour, juiciness, tenderness and overall liking.

Shear force (SHEARF5) is an indicator of the consumer perception of tenderness and is the force required to cut through a cooked sample of meat using a standardised cutting blade (SHEARF5). For this trait, shear force is measured in the loin muscle five days after slaughter to allow for tenderisation that occurs with ageing.

IMF has a moderate to high heritability and a high negative correlation with shear force. Therefore, as IMF increases, shear force reduces and tenderness increases. The heritability SHEARF5 is moderate to high. Without a balanced approach, lean meat yield (LMY) and eating quality can work against each other. This is because several eating quality attributes are adversely correlated with LMY. Therefore, selecting for high LMY alone will result in a high yielding animal that has low eating quality.

The terminal selection indexes have been developed with the aim of increasing growth and lean meat yield, whilst maintaining or improving eating quality. The Terminal Carcase Production (TCP) index is mostly contributed to by the growth and muscle traits post weaning weight (PWT) and carcase eye muscle depth (CEMD). The TCP index also has small contributions from carcase fat depth (CFAT), LMY and dressing percentage (DRESS). IMF and SHEARF5 are eating quality traits that have been included in the index at levels that consider the correlations between LMY and will lead to maintaining eating quality.

The Lamb Eating Quality (LEQ) index balances large improvements in eating quality with modest increases in lean meat yield, and includes emphasis on worm egg count ASBVs for production systems where internal parasites may cause economic losses. The LEQ index is mostly contributed to by the eating quality traits IMF and SHEARF5 at levels that consider the correlations with other traits in the index and will improve eating quality. High growth and carcase muscle is also favoured in the LEQ index where PWT and CEMD have strong contributions. Other traits that are considered in this index include CFAT, DRESS, LMY and worm egg count (PWEC).

Why select for eating quality?

Genetic selection pressure for high yielding carcases and carcase weight has led to an increase in LMY, causing a negative impact on the eating quality indicators of SHEARF5 and IMF. The preferred level of IMF in lamb meat is between 4% and 6% and lower shear force values represent more tender meat, with shear force of 3kg or less sought in lamb loin to achieve tenderness.

The industry phenotypic or mean value in 2018 for IMF was 4.3% and the range in Information Nucleus Flock lambs was between 2% and 7%. The mean shear force from the Information Nucleus Flock lambs was 2.4kg, with a range from 1.1kg to 7.7kg. This means that the average value sits only just above the minimum requirements for Australian lamb to meet consumer expectations. There is a large amount of variation around that average, meaning a lot of sheep meat is receiving eating quality scores that falls below the minimum requirements, and low volumes of sheep carcases receive eating quality scores that are the highest standard.

Since the implementation of eating quality ASBVs and their incorporation into terminal indexes, selection decisions have seen the trend in the industry average IMF ASBV plateau whilst LMY has been steadily increasing. This represents the opportunity to improve eating quality without sacrificing increasing LMY.

Meat standards Australia (MSA) has asked 38,000 consumers in 8 countries about their willingness to pay for varying levels of eating quality. Results indicate that compared to a pass or ‘good every day quality’, consumers were willing to pay:

o half or 0.5 times for a fail or ‘unsatisfactory quality’

o 1.6 times for ‘better than every day quality’

o 2.1 times for ‘premium quality’.

Eating quality is an important point of difference for red meats (beef and sheep meat) compared to white meats (pork and chicken). This is because ruminant animals (sheep and cattle) are relatively more expensive to produce than monogastric animals (pigs and chickens). This means eating quality is as important as improving efficiency through LMY% to justify to consumers the price premium for red meat.

Sheep producers can now be more aware of the impacts of selecting only for LMY, considering the requirements for demand for sheep meat to keep the industry strong. If the attributes are combined in the breeding objective, progress can be made simultaneously to improve both eating quality and LMY together.

Measuring eating quality

Currently there are no on farm methods to measure indicators of eating quality traits. Breeders, however, can get ultra sound scanning done for carcase traits and weigh animals to inform terminal indexes. Some breeds can get eating quality information via genetic linkages with animals that have been used in the resource flock. To get these linkages, purchase sires that have progeny or close relatives with progeny that have been selected as sires in the resource flock. You can also genotype animals in your flock to determine the genetic relationship with animals that have been directly tested for eating quality traits, but don’t appear directly in your animals’ pedigree. Genomic testing is available to Sheep Genetics members and the results are delivered via ASBVs.

A meat eating quality (MEQ) probe has recently been approved for use in sheep processing facilities in Australia. This technology will allow intramuscular fat measures to be taken on each carcase and supports the commercialisation of the new MSA sheepmeat cuts-based model. Sheep Genetics is currently investigating how we can incorporate the MEQ probe information into our analysis.

Proof for profit – MLA trials

The Meat & Livestock Australia (MLA) Resource Flock takes nominations every year to contribute semen to sire a cohort of progeny. These progeny are tested for a range of traits that are difficult to measure in typical ram breeding operations. The genetic links between these animals allow their test results to inform the traits of the rest of national flock.

Various trials have tested a range of traits and their impact on profit, including eye muscle depth, weight, carcase information, indexes, wool and reproduction. The results of these trials are available on the Sheep Genetics website. Go to sheepgenetics.mla.com.au then head to the Brochures and fact sheets page under the Resources tab and view the document ‘Proof of profit – using ASBVs – What’s in it for me?’. https://sheepgenetics.mla.com.au/resources/brochures-and-fact-sheets/

What can breeders be doing?

Looking forward, breeders can determine a breeding objective that aligns with their clients and the industry’s long term goals. A breeding objective should consider your production system and target market and any limiting factors.

MLA conducts market research to gain insight into what consumers want which is available on the MLA website. To ensure a high demand is maintained for sheep products, we as an industry need to account for what the consumer is willing to pay for. Market research has shown that consumers consider lamb a meat perfect for special occasions, likely due to their expectation of high quality and the high price for the products. Consumers want sustainable meat from happy, healthy animals that is the right size to fit 4 chops on a meat tray, doesn’t have too much external fat, and is in consistent supply.

ASBVs that relate to these consumer insights include:

Sheep Genetics encourages ram breeders to nominate sires for the MLA Resource Flock and get involved in satellite flocks. These programs ensure that the genetics present in the industry can be understood and improved. If you would like any further information from Sheep Genetics on the indexes, eating quality, consumer insights, or setting up a breeding objective, please get in touch and they would be happy to help - https://www.sheepgenetics.org