Principles of Animal Science and Production

[117.254]

Section D: Animal Growth & Meat Production

Nicola SchreursAH256; N.M.Schreurs@massey.ac.nz

Lecture 3

D.4: Meat quality characteristics

This group of characteristics is more difficult to study scientifically

than growth or composition characteristics for several reasons:

1. The word “quality” has more than one meaning. Here it is taken to mean the “Level of goodness” rather than the “Fitness for purpose”.

2. Meat or meat-animal quality encompasses different characteristics by people at different points in the meat-production chain (Figure D.4, p22).

3. The consumers vary in the emphasis they place on different components of meat quality and in the preferred level of some characteristics (e.g. by race, sex, age, occasion, etc).

Stage in the meat production

chain

Components of “Quality” of

importance

MEAT at the time of

consumption

1. Palatability

2. Appearance

3. Nutritive value

4. Safety & wholesomeness

MEAT PRODUCT at the time of

retail purchase

1 to 4 above +

5. Edible meat yield

6. Ease of preparation

7. Storage requirements

8. Credence attributes

MEAT CARCASS being bought

by the butcher

1 to 8 above +

9. SMY% from the carcass

10. % in the high-priced cuts

11. Shape of the carcass (e.g. muscularity)

12. Processing properties

STORE ANIMAL being bought

by the farmer to finish

1 to 12 above +

13 The animal’s growth potential

14 Dressing-out %

15 Complementarity

Characteristics contributing to “quality” at different

points in the chain (Figure D.4)

Meat quality characteristics 1. Appearance & Palatability

(Table D.11)

Appearance characteristics• Lean meat colour [red to pink is favoured]

– Mainly due to the amount and form of myoglobin– Measured subjectively, or objectively by reflectance, or VIA

• Fat colour [yellowness is the main problem]– Mainly due to the concentration of carotenoids– Measurements as for meat colour

• Meat texture [fine texture tends to be favoured]

• Firmness and composition.

Palatability characteristics• Tenderness [the force required to bite through]

• Flavour [determined by both taste and aroma]

• Juiciness [affected by water content and fat content]– Both subjective and objective measurement methods are used– All 3 are complex characteristics.

Meat quality characteristics 2. Nutritive value (Table D.11)

Important characteristics of lean meat as a source of nutrients in the human diet:

• “Nutrient dense” with respect to protein & several other nutrients

• Contains ~22% of high quality proteins

• It is usually highly digestible

• A good source of Fe and Zn, with the haem Fe being highly bioavailable, and a “meat factor” being present

• A good source of most B vitamins, esp. B12

• Lean meat has a low fat content (usually)

• Cholesterol levels are moderate at 70-80 mg·(100 g)-1

• Meat is not a good source of Ca, vit C, and dietary fibre

• Lipid in the lean meat of ruminants contains 25-40% of fatty acids as saturated FAs.

Meat quality characteristics 3. Other components of meat

quality (Table D.11)

Processing properties of meat• WHC, binding capacity, emulsifying capacity.

Safety & wholesomeness characteristics• Microorganisms

• Residues

The focus in this paper will be on appearance and palatability characteristics because they are usually the most variable.

Some approaches to the measurement of meat quality are covered briefly in the Study Guide.

More details on the characteristics within meat responsible for its appearance and palatability will be covered in the section on factors affecting these characteristics.

D.5. Seven stages at which growth, composition or meat

quality may be affected (Table D.12, p27)

1. In the choice of the type of animal to run

4 sources of variation given in Table D.12

2. In the choice of the age or weight end-pointUsually target weights, dates, or level of finish are used

3. In the choice of on-farm treatments

5 aspects listed in Table D.12

4. In the choice of pre-slaughter treatment

4 aspects listed in Table D.12

5. In the choice of pre-rigor conditions

3 points to consider given in Table D.12

6. In the choice of post-rigor but pre-cooking conditions

4 examples of important variables given in Table D12

7. In the choice of cooking conditions

3 aspects of importance listed

Factors affecting growth, carcass and meat

quality characteristics

• Have considered growth, carcass and meat quality

characteristics – you should know what these are.

• Now go on to consider how the growth, carcass and

meat quality characteristics are affected by different

factors – i.e., consider why there are differences in the

characteristics.

D.5 (a): Possible reasons for growth rate differences?

Why might one animal grow faster than another similar animal in the

same environment?1. It eats more, and/or

2. It digests & absorbs the feed it eats more effectively, and/or

3. It metabolises the nutrients with less heat loss, and/or

4. It has lower protein turnover rates in key tissues, and/or

5. It has a lower proportion of more active tissues, and/or

6. It is less affected by diseases, and/or

7. Other factors

Picture of Borderdale ram hoggets from “Sheep Breeds of New Zealand” by Graham Meadows (1997)

Possible metabolic explanations of variation in growth:

The somatotrophic axis (Figure D.5, p28)

+ -Hypophysial Portal Vein Blood

GH in General Circulation

Hypothalamus(in the brain)

Anterior Pituitary

LiverMuscle Fat Bone

IGF-I in General Circulation

IGF-1Insulin-like

Growth Factor-1

Body

Tissue

[GH may also

stimulate IGF-1

production within the

target tissues, such

as adipose tissue or

bone.]

GRHGrowth Hormone

Releasing Hormone

Somatostatin

Growth Hormone (GH)(Somatotrophin)

Some biological effects of GH (somatotrophin) in farm

animals

1. Increased protein synthesis in skeletal muscle.

2. Increased mineral accretion in bone.

3. Increased milk synthesis in lactating animals.

4. Decreased lipid synthesis in adipose tissue of animals

in a positive energy balance.

5. Increased lipolysis in adipose tissue for animals in a

negative energy balance.

6. Increased IGF-1 mRNA abundance in adipose tissue.

7. Decreased adipocyte hypertrophy.

8. Increased intestinal levels of Ca-binding protein.

9. Increased plasma levels of IGF-1 and IGFBP-3.

10. Increased cardiac output in lactating animals.

[Etherton, T D (2004) J.Anim.Sci. 82: E239-E244.]

Examples of factors affecting animal growth rate other

than nutrition (Table D.13)

Growth rate at a particular stage of development will be

greater for:

Breeds with higher mature weights• Because of +ive genetic relationships between mature weight and ADG

Castrate males relative to females for ruminants• The opposite is true for pigs

Animals following a period of nutritional restriction relative to unrestricted animals

• A phenomenon referred to as compensatory growth (next slide)

Steers that have been treated with hormonal growth promotants (HGPs; eg oestradiol 17β)

• Due in part to increased GH production

Compensatory Growth (Item 3 in Table D.13)

b

a

Differential feeding period Uniform feeding period

Liv

e w

eig

ht

Time

Compensatory Growth = The faster growth rate of a group of animals following

a period of restricted feeding (the “differential feeding period”), relative to a

control group that was not restricted.

Degree of compensation (%) = [(a – b)*100]/a

Restricted

group

Control

group

Factors affecting body composition: (1) Cell recruitment.

Undifferentiated

“stem” cell or

primitive

mesenchyme cell

Myoblast →Muscle tissue

Osteoblast →Bone tissue

Pre-adipocyte →Adipose tissue

Fibroblast →Connective tissue

Chondroblast →Cartilage tissue

Several other specialised cell types“R

ecru

itm

en

t”o

r“co

mm

itm

en

t”

an

d d

iffe

ren

tia

tio

n

The Biological Mechanisms Responsible for “Recruitment” of Undifferentiated Cells

may Affect Body & Carcass Composition

Factors affecting body composition: (2) The cellular basis

of growth (Figure D.6)

1. Growth by an

increase in cell

number

(hyperplasia)

2. Growth by an

increase in cell

size

(hypertrophy)

3. Growth by an

increase in non-

cellular material

(accretionary

growth)

Three ways of achieving an 8-fold increase in size:

The relative contribution of these three may influence subsequent capacity to grow

Factors affecting carcass composition: Examples (Table D.14)

• Lower carcass fat% at a set weight from:• Higher mature weight [because they are less mature]

• Being entire males [due to androgens]

• Genetic selection [due to moderate h2 of fat%]

• Less feed (?) [not a consistent effect]

• Higher P/E ratio [due to extra protein]

• GH treatment [due to effects on lipid & protein metabolism]

• Following winter [physiological basis unclear]

• Higher carcass M:B at a set weight from:• Selection for M:B [due to h2 of M:B & muscling]

• MH gene [due to effects on fibre number and size]

• Callipyge gene [due to more calpastatin]

• Ewe vs ram lambs [due to a lighter skeletal structure(?)]

• ßAA treatment [due to more calpastatin]

Principles of Animal Science and Production

[117.254]

Section D: Animal Growth & Meat Production

Nicola SchreursAH256; N.M.Schreurs@massey.ac.nz

Lecture 4

Factors affecting meat quality: Important features of

skeletal muscle

• Skeletal muscle or lean meat is made up of >96% muscle fibres with the balance being mainly connective tissue and adipose tissue.

• Muscle connective tissue is at three sites:

• Epimysium around the whole muscle

• Perimysium around bundles of muscle fibres

• Endomysium around individual fibres

• Key differences between skeletal muscle fibres and most other tissues include:

• It is a multinuclear syncitium

• The nuclei within the fibre do not divide

• The presence of myoglobin

• A highly developed contractile system

• A hierarchical structure, with fibrils within fibres and filaments within fibrils

Muscle structure at the sarcomere level(Figure D.7, p 34)

Sarcomere length is an important determinant of meat tenderness,

↑ SL ↑ tenderness

The sequence of some key post mortem changes

occurring in muscle

• Loss of O2 with bleeding (exsanguination)

• Switch from aerobic metabolism to anaerobic glycolysis

• Lactic acid accumulation causes a drop in pH

• Big reduction in the efficiency of ATP production

• A drop in [ATP] triggers the onset of rigor mortis (loss of extensibility)

• pH ceases to drop at about 5.5 when glycogen levels are adequate

• Depleted glycogen levels at slaughter can lead to high ultimate pH levels in meat with important implications for several meat quality characteristics

Examples of factors affecting meat tenderness (Table D.15, p36)

Meat is likely to be less tender from:

• Bos indicus cattle [due to less protease activity]

• Callipyge lambs [due to more calpastatin]

• Bulls vs steers [several possible explanations]

• Older animals [due to collagen that is less soluble]

• Poorly-fed animals [may be age or weight effects]

• Intermediate-pH meat [reasons for this are unclear]

• Early-chilled meat [due to cold-shortening]

• Unaged meat [due to less proteolytic activity]

• Poorly cooked meat [several possible explanations]

• More connective tissue [a collagen effect]

The relationship between collagen concentration and

tenderness across muscles (p. 33 & Table D.15)

Increasing toughness with increasing collagen

content across several beef muscles

y = 66.829x + 74.506

R2 = 0.8882

50

100

150

200

250

300

0 0.5 1 1.5 2 2.5 3

Muscle collagen content (%)

WB

sh

ear

(N)

Tenderness was measured

mechanically on cooked

samples to give shear-force

values.

Muscles were chosen to cover

a wide range of collagen

content (from psoas major to

shin muscles).

Within the same muscle,

collagen levels are not closely

related to tenderness.

[Meat Science (2003) 63(2): 161-168.]

Decreasing the chances of cold-shortening and

toughening by modified hanging (Table D.15, item 7)

Stretched muscles

of leg and back

Less stretched

muscle

Carcasses are normally hung

from the achilles tendon which

permits many muscles to

shorten (diagram on right).

Hanging from the hip, as

shown, results in more of the

more valuable muscles being

unable to shorten, thereby

increasing the likelihood of

tender meat.

Electrical stimulation is a

more widely used method of

minimising cold-shortening.

Changes post mortem in meat/muscle pH & inextensibility (Figure D.8)

pH drop (due to lactic acid

accumulation) is

accelerated by ES due to

muscle contraction.

Increased inextensibility (due

to low [ATP]) occurs sooner

when muscle is electrically

stimulated.

Factors affecting the colour of meat or fat(Table D.15, p37)

Meat/fat colour can be affected by:• Connective tissue/Intramuscular fat levels [due to dilution effect]

• Breed of cattle for fat colour [due to carotenoid]

• Meat ultimate pH [for several reasons]

• The rate of pH decline [due to high temp-low pH]

• An O2-rich atmosphere [due to more MbO2]

• Concentration and form of Mb [main determinants of meat colour]

• Deoxymyoglobin {purplish-red} fresh cut surface

• Oxymyoglobin {bright red} colour of “bloomed” meat

• Metmyoglobin {brown} Fe++ oxidised to Fe+++

Myoglobin and meat colour

Deoxymyoglobin

Fe2+

Purple-red

O2

oxygenation

Metmyoglobin

Fe3+

Brown

Oxymyoglobin

Fe2+Bright red

Electron loss

oxidation

An example of factors affecting meat colour through the form of

myoglobin on the meat’s surface (Table D15)

• Consumers avoid meat with metmyoglobin levels >30% due to its brownness.

• In this trial Wagyu beef on retail display was assessed over 12 days @ 4 C.

• Shelf-life of tenderloin was only about 3 days, while that for striploin from younger

cattle (24 mo) was up to 9 days.

Asian-Australasian J.Anim.Sci. (2003) 16(9):1364-1368

Criterion Application in NZ

1. Animal age/maturity Yes, for beef, sheep, deer, & pigs

2. Animal gender Yes, for older classes only for some species

3. Carcass fatness Yes, for all species

4. Carcass shape Yes for beef, but not other species

5. SMY% or LMY% Not directly for any species

6. Fat colour To a limited extent for beef and lamb

7. Muscle/meat colour Only for some beef for certain markets

8. Marbling level Only for some beef for some markets currently

9. Ultimate pH Intermittently; mainly for some prime beef

10. Carcass weight range Yes, for all species in a step/stair pattern

11. Other meat quality items No.

D.6: Carcass classification criteria used in NZ & elsewhere

Depths of fat or soft-tissue used for carcass classification(Figure D.9)

Fat depth

C, D, or P2

Soft-tissue

depth GR

“Eye”-

muscle

Standard photographs of lamb carcasses used for scoring

conformation in the UK