This was one of the conclusions from a recent on-farm trial looking at the links between feed, breed and gender on saleable meat yield. A group of 15 top-performing North Island farmers, who supply lambs to Progressive Meats, used Beef + Lamb New Zealand farmer-initiated technology transfer funding to analyse the records for 42,000 lambs across two seasons. They worked with geneticist Aimee Charteris and looked for patterns and insights into on-farm factors influencing saleable meat yield, as well as carcase weight and fatness.
Lambs from the 15 producers' properties were involved in the trial, which ran over the 2011/12 and 2012/13 seasons. Information was recorded on farm prior to processing, then compared against the individual animals' carcase weights, fatness levels and saleable meat yields. Results were consistent between the two seasons.
Group spokesperson Stuart Ellingham, general manager at Horizon Farming Limited, says the trial analysis reinforced to him the importance of treating different sexes of lambs differently.
"The main message I took out of the trial was that farmers tend to treat lambs as lambs. They don't separate out different sexes and recognise what the different sexes are doing at different times of the year. This method of management is particularly noticeable in terminal-sired lambs, where all sexes tend to be treated the same. An entire male lamb is different from a wether lamb, which is different from a cryptorchid, which is different from a ewe lamb."
Stuart says these differences are notable in autumn, when lambs reach sexual maturity. "If we are going to leave male lambs entire, we need to process them by February to optimise their meat characteristics – that is, the dressing out percentage and saleable meat yield. Both are important.
"When it comes to female lambs, you don't want to be killing them in March or April. Their meat quality characteristics that you are paid for – depending on your processor – drop right off over that period. So process before or after that."
Trends for carcass weight (CW), level of fatness in the carcass (GR) and saleable meat yield (SMY) for November 2011 to September 2013. Results for lambs born in 2011 (top) and 2012 (bottom).
Other gender differences
At the same age, ewe lambs were fatter, on average, than male lambs. However, there was no significant difference between carcase weight and saleable meat yield. Ewe lambs should therefore be processed earlier than male lambs, if the processing specifications demand lower fat cover.
Identifying different sexes – particularly of terminal-sired lambs – and adjusting their feeding regime and timing of processing can improve the bottom line. For example, to avoid ewe lambs having a lower saleable meat yield, they could be separated at weaning, condition score monitored and processed earlier, at lower liveweights than males.
In another example, castrating small male lambs at docking and leaving bigger male lambs entire – to be processed pre-autumn – avoids a drop in saleable meat yield during autumn.
Single-born lambs were heavier, fatter and had lower saleable meat yields, compared to twin lambs. Single born lambs should be processed earlier to achieve better saleable meat yields, although further investigation is needed to determine the optimal age. There may also be a need to easily identify single-born lambs, at drafting time.
Breed differences for carcase weight, fatness and saleable meat yields were recorded and were consistent with industry experience.
Effect of different feed types
There were significant differences in carcase weight and fatness and meat yield across the lambs, when fed different feed types, but the results were not consistent over the season. Aimee says a more structured trial is planned for next year. "So we can make sure we identify exactly what the effect is and the size of effect and ensure it absolutely is the feed type that is causing the significant differences."
Seasonal variations in saleable meat yield
Across the supply season – October to September – there were considerable decreases in saleable meat yield, particularly through March and April – and across both seasons (see graphs). The variations were linked to a combination of declining feed quality and lambs reaching sexual maturity. The group concluded that it was financially worthwhile for individual farmers to evaluate their own systems to identify opportunities to address this March/April yield drop off.
Before on-farm changes can be recommended, more work is needed to understand breed and feed variations. There is also potential to investigate the correlation between dressing out percentage and saleable meat yield.
Download a copy of the project final report
How on-farm factors influence saleable meat yield (PDF, 1MB)