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  • Tracey Jensen


It is a beautiful thing when science and stockmanship find some common ground. Such is the case for the recent realisation of the value of increasing the genetic fat and muscle in Merino ewes.

Meet the 'bullet proof' sheep

In what could be described as parallel universes two dedicated sheep teams made exactly the same discovery: The more genetic fat and muscle a Merino ewe has the better she handles the climatic extremes, that is, the more bullet proof she is.

Team 1: The Murphy family, Karbullah Poll Merinos, Goondiwindi. The Murphy’s, with their keen eye for stock that can handle the tough conditions of Queensland, started to notice that particular ewes and rams were handling the tough times better than others. When they looked a little harder they noticed that the ewes and rams that were handling the conditions the best were those that high Australian Sheep Breeding Values (ASBVs) for fat and muscle. They immediately responded and put positive selection pressure on both of these traits.

Around the same time about 3500 km away in Perth, WA, Team 2, Mark Ferguson and Andrew Thompson and their research team, were busy investigating the role genetic fat and muscle could play in improving the maternal capacity of the Merino. What they found lined up exactly with what Mark and Vicki Murphy at Karbullah had found: When it comes to breeding Merinos, genetic fat and muscle are absolute must haves.

Fat plays an essential role in the reproductive process and sufficient fat reserves are necessary for animals to ovulate and successfully reproduce. Similarly, total body muscle is also an important resource for animals to draw on in tough times and is also important in driving reproduction.

The research has shown that ewes with higher fat ASBVs:

  • Lose less liveweight when nutrition is restricted

  • Have higher reproduction rates, particularly when nutrition is restricted during mating (as high as 25 extra lambs per 100 ewes mated per 1mm of extra genetic fat)

  • Produce lambs with higher birthweights when nutrition is restricted – that is lamb birth weight is buffered by the genetic fat , increasing the likelihood of the lamb surviving

  • Have lambs that have better survival to weaning – about a 5% increase in lamb survival per 1mm increase in genetic fat

  • Have weaners that also survive better – this effect is bigger in small weaners as a result of tough years but normally around a 2.5% increase in weaner survival per 1mm increase in genetic fat

In short, by putting some genetic fat back on your ewes can help make them bullet proof to climate variability. When the benefits are all added up and put through a whole farm model, the value of increasing genetic fat by 1mm in a Merino ewe flock is over $10 per ewe per year.

What about muscle? The great thing is the two come together, Merino sheep with good muscle breeding values also tend to have good fat breeding values. What are the positive attributes of sheep with good muscle?

They tend to:

  • Produce more twins (about 6 extra lambs per 100 ewes mated for an extra 1mm of muscle)

  • Remain in higher body condition score throughout the year

  • Have less worms and better staple strength

  • As an added bonus they also produce better carcasses which have higher dressing percentages

In simple terms, Merino sheep that have high genetic fat and genetic muscle just do better – they are bullet proof. There are not many free lunches in sheep farming but this is one of them.

For commercial producers the key to capitalising on this opportunity is the effective use of ASBVs in ram buying decisions. You cannot visually see 1mm of muscle or 1mm of fat on a ram it must be measured. Equally raw measures of fat and muscle (ie not ASBVs) are useless, they must be corrected for liveweight and converted into an ASBV to get the full picture of an animal’s worth.

Some tips for ram buyers wanting to capitalise on this opportunity:

  1. Make a plan for your ewe flock – Decide on the key traits that will make you money

  2. Find a ram source that is supplying ASBVs for yearling fat (YFAT in the catalogue) and yearling muscle (YEMD in the catalogue) as well ASBVs for the other traits that make you money

  3. Look for rams that are greater than +1mm for YEMD and greater than +0.5mm for YFAT, these rams are in the top 30% of the breed of the current drop for these traits

  4. Of the rams within (or near) these cutoffs find the ones that are visually appealing , have the right wool, and have favourable ASBVs for the other traits that make you money

  5. Get to know worm egg count (YWEC) breeding values as well, very important for Barbers Pole environments, can help to bullet proof the ewes and young sheep

  6. Be prepared to be flexible, the perfect rams aren’t always easy to find, but get as much positive muscle and fat as you can while sticking to your normal ram buying criteria

  7. Talk to your ram breeder about the plan you have for your flock and the traits that you are aiming to improve

  8. If ASBVs seem all too difficult find someone who can explain them to you – a neighbour, someone from leading sheep, your ram breeder

  9. When used wisely and with good stockmanship ASBVs are an unbelievably powerful tool at improving the profitability of Merino sheep

So where did the fat and muscle go? They went into wool! For two centuries we have been breeding for higher wool quality and higher wool cuts.

This breeding strategy inadvertently reduced the genetic fat and muscle in Merinos, its time to bring it back to help make sheep easier to manage and produce more lambs.

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