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- 1. Muscling & eating quality Peter McGilchrist, Kirsty Thomson, Graham Gardner, Dave Pethick Robin Jacob
- 2. Selection for Muscling •Feed efficiency •Dressing percentage •Saleable meat yield Muscling desirable because
- 3. Could selection for muscling affect meat quality? Meat quality
- 4. MSA grading pHu = 5.5 pHu = 6.04 High pHu/dark colour-main reason for failure to grade MSA
- 5. High pHu Tenderness Flavour Visual Food safety MSA Tough pH 5.7-6 Off flavours Dark Colour score >3 Favours bacterial growth Fail Rubbery pH>6 Stays red after cooking Poor keeping quality Costs per carcase $50 $36M Dry
- 6. Muscling/pHu study 1. Abattoir data investigation 2. Muscling experiment
- 7. • Funded by Beef CRC • MSA grading data • One abattoir • Feb 2002 - Dec 2008 • Lots records -207, 041 carcases • Is pHu associated with eye muscle area? Abattoir data
- 9. EMA vs pHu 5.52 5.54 5.56 5.58 5.6 5.62 5.64 5.66 5.68 5.7 20 30 40 50 60 70 80 90 pH(predcited) Eye Muscle Area (cm2) •Larger loins tend to have a lower pHu on average •Lower average pHu = less dark cutting
- 10. HCW 5.52 5.54 5.56 5.58 5.6 5.62 5.64 5.66 5.68 5.7 20 30 40 50 60 70 80 90 pH(predcited) Eye Muscle Area (cm2) 150 HSCW 250 HSCW Higher carcase weight lower pHu
- 11. Effect across carcase weight 5.45 5.5 5.55 5.6 5.65 5.7 20 40 60 80 100 120 pH(predcited) Eye Muscle Area (cm2) 150 HSCW 250 HSCW 350 HSCW 450 HSCW Within each HCW Big loin low pHu
- 12. Looks good but why? • Large industry data set • Lots of factors mixed together • Muscling • Age • Finishing • Other Need more proof for muscling effect
- 13. Muscling experiment • Muscle fibre distribution • Hormone sensitivity depends on fibre type
- 14. Fibre types More fast twitch fibres Slow twitch IA Intermediate IIA Fast twitch IIX Slow twitch IA Intermediate IIA Fast twitch IIX Selection for muscling
- 18. Hypotheses 1.Lower response to adrenalin 2.Greater response to insulin 3.More glycogen in muscle Cattle selected for muscling will have:
- 19. Adrenaline Response 0 5 10 15 20 25 30 35 0 0.5 1 1.5 2 2.5 3 Adrenaline Challenge (ug/kg Liveweight) LactateAreaUnderCurve(mM/20min) High Muscled Low Muscled
- 20. Insulin Sensitivity InsulinSensitivity 0 100 200 300 0.6 µg/kg/min 6.0 µg/kg/min GlucoseInfusionRate(ml/hr) Insulin Infusion Rate Low Muscled High Muscled
- 21. Muscle Glycogen 1.45 1.5 1.55 1.6 1.65 1.7 High MuscledLow Muscled GlycogenConcentration(g/100g)
- 22. Hypotheses 1.Lower response to adrenalin 2.Greater response to insulin 3.More glycogen in muscle Cattle selected visually for muscling will have: Now have proof
- 23. Overall conclusion Muscling + Yield + Glycogen Muscling experiment Hormone response Less adrenaline More insulin More glycogen Abattoir data pHu correlated with EMA Large loin low pHu
- 24. Acknowledgements Dr Graham Gardner Professor David Pethick Dr Paul Greenwood Dr Kirstie Thomson CRC for Beef Genetic Technologies Murdoch University
Notes de l'éditeur
- Within the beef industry, retail beef yield is a huge profit driver as it improves animal efficiency in converting food to protein and improves productivity and profitability of processing plants, and this image here on the right clearly highlights the increased muscle and reduced fatness of a high yielding carcases compared to a low. For this reason retail beef yield is selected for using genetic technologies and In recent years substantial gains in retail beef yield have been made within the industry
- The big question is… WOULD THIS be supported by a BIG INDUSTRY DATA SET??? (Big Pause…)
- … Low muscle glycogen at slaughter. You see after death the muscle continues to metabolise anaerobically converting the stored muscle glycogen to lactic acid, dropping the pH down to an ultimate level of about 5.5. But if there is not enough glycogen, the pH will remain elevated, and if it is too high you’ll get dark cutting meat.
- And the slide you can see here clearly illustrates the colour difference between a normal and a dark cutting piece of steak Now this problem currently costs the industry 35mil because of its impact on meat quality, and it is caused by…
- To test this we used 7 years worth of beef grading data gathered by MSA at a large WA abattoir that contained over 207, 000 carcass records. Ultimate pH was analysed using a linear mixed effects model in SAS, we adjusted this model for a range of environmental factors,
- and specifically used Eye Muscle Area corrected for carcase weight as the indicator of muscularity.
- So this clearly indicates that increasing EMA is associated with a reduction in average ultimate pH and a reduction in the incidence of dark cutting.
- Well you will remember more muscular cattle have been shown to have more fast-glycolitic Type IIX fibres and less oxidative Type I and IIA fibres.
- And we were thrilled to see that our expectations for muscling held up within this data set... Here you can see that as EMA increases, the ultimate pH decreased particularly in the lighter 150kg carcases with this decrease of about 0.05 pH units (Click) equivalent to a 12% reduction in dark cutters.
- And we were thrilled to see that our expectations for muscling held up within this data set... Here you can see that as EMA increases, the ultimate pH decreased particularly in the lighter 150kg carcases with this decrease of about 0.05 pH units (Click) equivalent to a 12% reduction in dark cutters.
- So at this early stage of our work we were hypothesising that …
- But this theory was quickly undone by the results of our initial experiments, where we carried out controlled metabolic studies in a small group of Angus cattle selected for high (point at blue line) and low (point at red line) muscling. As you can see from this graph, under increasing adrenaline challenge (be pointing at axis!), the muscle response (now point at y axis) to adrenalin was actually less (click!) in the high muscling selection line. Which would suggest that these cattle are actually mobilising less glycogen under stress! (pause)
- In addition to this we also looked at whole body insulin sensitivity using a hyper insulinaemic euglycaemic clamp. This methodology involves infusing insulin at a constant rate, firstly at 0.6 ug/kg/min, and then at 6.0 (point at graph legend). This will cause blood glucose to drop, so you then infuse glucose (now point at Y axis) at a rate to maintain it at constant levels in the blood. So the more insulin responsive the animal, the quicker you’ll have to infuse glucose (point at Y axis again). (click!) And you can see that it was the high muscled animals were more responsive at both the 0.6 (point at graph) and 6.0 ug/kg/min (point at graph) insulin infusion rates. And this would lead to greater muscle glucose uptake and storage as glycogen in response to nutrition. Now the adrenalin and insulin results in combination were actually quite exciting because they seemed to suggest that not only were our initial hypotheses wrong, but that high muscled animals would actually have more stored muscle glycogen!!! And guess what…
- They did!!!!! As you can see, in this small herd the high muscled group had about 6% more muscle glycogen. So at this stage we were becoming pretty confident that we were on to a winner with high muscling cattle!!!!
- So at this early stage of our work we were hypothesising that …
- However none of this work would have been possible at all without the fantastic support from my supervisors and collaborators on this project as well as funding from the CRC for Beef genetic technologies, Murdoch University