Muscling & eating quality

Peter McGilchrist, Kirsty Thomson,

Graham Gardner, Dave Pethick

Robin Jacob

Selection for Muscling

•Feed efficiency

•Dressing percentage

•Saleable meat yield

Muscling desirable because

Could selection for muscling affect meat quality?

Meat quality

MSA grading

pHu = 5.5 pHu = 6.04

High pHu/dark colour-main reason for failure to grade MSA

High pHu

Tenderness Flavour Visual Food safety MSA

ToughpH 5.7-6

Off flavours

Dark Colour score >3

Favours bacterial growth

Fail

RubberypH>6

Stays red after cooking

Poor keeping quality

Costs per carcase $50

$36M

Dry

Muscling/pHu study

1. Abattoir data investigation

2. Muscling experiment

• 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

Eye muscle area

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

(p

red

cit

ed

)

Eye Muscle Area (cm2)

•Larger loins

tend to have a

lower pHu on

average

•Lower

average pHu =

less dark

cutting

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

(p

red

cit

ed

)

Eye Muscle Area (cm2)

150 HSCW 250 HSCW Higher carcase weight lower pHu

Effect across carcase weight

5.45

5.5

5.55

5.6

5.65

5.7

20 40 60 80 100 120

pH

(p

red

cit

ed

)

Eye Muscle Area (cm2)

150 HSCW 250 HSCW

350 HSCW 450 HSCWWithin each HCWBig loin low pHu

Looks good but why?

• Large industry data set

• Lots of factors mixed together

• Muscling

• Age

• Finishing

• Other

Need more proof for muscling effect

Muscling experiment

• Muscle fibre distribution

• Hormone sensitivity depends on fibre type

Fibre types

More fast twitch fibres

Slow twitchIA

IntermediateIIA

Fast twitchIIX

Slow twitchIA

IntermediateIIA

Fast twitchIIX

Selection for muscling

Hormone sensitivity

Slowtwitch

IA

IIB

Fasttwitch

IIX

Adrenaline

Insulin

Muscling

FeedInsulin

Fill glycogen bucket

Feed

pHu <5.7

pHu >5.7

Stress

Empty glycogen bucket

Adrenaline

Hypotheses

1.Lower response to adrenalin

2.Greater response to insulin

3.More glycogen in muscle

Cattle selected for muscling will have:

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)

La

cta

te A

rea

Un

de

r C

urv

e (

mM

/20

min

)

High MuscledLow Muscled

Insulin Sensitivity

Insu

lin S

ensi

tivi

ty

0

100

200

300

0.6 µg/kg/min 6.0 µg/kg/min

Glu

cose

In

fusi

on

Rat

e (m

l/h

r)

Insulin Infusion Rate

Low MuscledHigh Muscled

Muscle Glycogen

1.45

1.5

1.55

1.6

1.65

1.7

High MuscledLow MuscledGly

co

ge

n C

on

cen

trati

on

(g

/100

g)

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

Overall conclusion

Muscling+ Yield

+ Glycogen

Muscling experiment

Hormone responseLess adrenalineMore insulin More glycogen

Abattoir data

pHu correlated with EMALarge loin low pHu

Acknowledgements

Dr Graham GardnerProfessor David Pethick

Dr Paul GreenwoodDr Kirstie Thomson

CRC for Beef Genetic TechnologiesMurdoch University