Heat tolerance and tenderness

Tracy Scheffler UF Department of Animal Sciences

Brahman On the pasture• Heat tolerant• Parasite resistance• Lower maintenance requirements

On the plate• Variation in tenderness• Lower marbling

Angus Brahman

Key questions:• What features and adaptations

make Brahman heat tolerant? Brahman are resilient

• Is heat tolerance related to meat quality? Meat – a product of life and death

Angus Brahman

Heat tolerance

Heat loss or gain with environment

Heat production from metabolism

Heat exchange between the animal and the environment

Evaporation - sweat

Evaporation - water from skin & breath

Conduction - ground

Convection - air

Radiant energy -sun

• Animal surface area : weight• Temperature gradient, animal vs. air• Hair coat

Heat loss in Brahman

Evaporation - sweat

Evaporation - water from skin & breath

Conduction - ground

Convection - air

Radiant energy -sun

Smooth, slick, light-colored hair

More sweat glands

Loose skin ↑ surface area

Heat production (metabolic rate)

• Basal metabolism

• Digestion• Physical Activity• Production (growth)

• Whole body • Organs differ in metabolic activity & size

Organ contribution to body metabolism% of body weight % basal metabolic rate

• Metabolic activity based on total weight• Metabolic activity on per unit basis

Brain2%

Heart0.5%

Kidneys0.4% Liver

2.6%

Digestive system20.0%

Muscle40%

Fat Mass21%

Other14%

Brain12%

Heart8%

Kidneys7%

Liver19%Digestive

system25%

Muscle20%

Fat Mass3%

Other6%

Heat production (metabolic rate) in Brahman

• Basal metabolism• Digestion• Physical Activity• Production (growth)

• Lower maintenance requirements• Smaller organ size• Metabolism on a per unit (cell) basis?

Heat production (metabolic rate) in Brahman

Basal metabolism

Muscle tone

other

Protein synthesis

Ion gradients

Ener

gy fo

r mai

nten

ance

What do cells use energy for?

Muscle tone

What affects energy requirements?“Uncoupling” processes increase energy demand & metabolic rate

• Protein degradation• Ion leaks• Muscle relaxation

other

Protein synthesis

Ion gradients

Ener

gy fo

r mai

nten

ance

Protein metabolism

Decrease protein degradation Limit metabolic rate

Limit heat production

Protein Synthesis

ProteinDegradation

= Protein Deposition -Protein turnover

• Heat tolerance? • Growth rate? • Meat quality?

Protein synthesis

Protein degradation contributes to tenderness during meat aging

1h postmortem 24h postmortem

Evaluating postmortem protein degradation

• Calpain (cuts proteins)• Calpastatin (inhibitor)• Calpain : calpastatin• Breakdown of individual proteins

0.01.02.03.04.05.06.07.0

0.20 0.40 0.60 0.80 1.00Protein degradation

Very tender

Moderately tough

Increasing Brahman composition

Elzo et al., 2012

On average, decreases protein degradation and tenderness

• Decreased protein degradation in living animal?

• Hypothesis:Slower growing Brahman will have reduced protein synthesis and degradation, resulting in decreased growth rate, low metabolic rate, and greater heat tolerance

…and tougher beef

Heat tolerance, growth, & tenderness in Brahman

Calves born

Dec.-Feb.

Weaning

Aug.

Select for high & low growth

Oct. June

Acclimation & Heat challenge (2 wk)

Finishing at BTU

SlaughterUF Meat Lab

Dec.

• Respiration• Temperature• Biopsy (pre- and post-)

• Carcass data• Muscle samples –protein degradation

• Aged steaks for tenderness

Heat challenge

70

75

80

85

90

95

100

105

101.0

101.5

102.0

102.5

103.0

103.5

104.0

-6 -4 -2 0 2 4 6 8 10 12 14 16 18 20day

Day P < 0.0001

Growth P = 0.70

Day * Growth P = 0.25

0102030405060708090

100

-6 -4 -2 0 2 4 6 8 10 12 14 16 18 20day

Day P < 0.0001

Growth P = 0.84

Day * Growth P = 0.82

Temperature - rooms Rectal temperatureRespiration rate

(breaths/min)

Meat quality (n = 16 total)

0

2

4

6

8

10

12

Standard Select Low Choice

Freq

uenc

y

Quality Grade

0123456789

moderatelytough

slightly tough slightly tender moderatelytender

Freq

uenc

y

Sensory rating

TendernessAvg shear force = 3.1 kg (2.1 – 3.7 kg)

Brahman & tenderness

• Marbling ?Not improving sensory tenderness

• Protein degradation?Improves likelihood for favorable tenderness

200

250

300

350

400

450

500

3 4 5 6 7

Mar

blin

g

Sensory tenderness Mod. tenderMod. tough

Standard

Select

Low choice

0

0.05

0.1

0.15

0.2

3 4 5 6 7

Prot

ein

degr

adat

ion

Postmortem protein degradation in Brahman

• Calpain activation • Slower in Brahman • Slower activation ↑ toughness

0

0.2

0.4

0.6

0.8

1

0 24 72 168 336Time (h)

Calpain activation - Brahman

(14d)

What affects calpain activation?Calpastatin (inhibitor)

• Slower disappearance in tougher steaks• Degraded by calpain• Greater content?• Capacity for inhibition?

• Calcium• Temperature• pH

Calpastatin

Postmortem metabolism

Living muscle Dying muscle/meatpH 7.2 ↓ to 5.6

Temp. 101°F ↓ to < 40°F

Energy Stable / recoverable Gradually depleted

Intracellular Calcium tightly controlled Calcium ↑

Postmortem metabolism: Conversion of muscle to meat

Rigor mortisCa2+ increases

ATP (energy)

ATP depletedMaximal tension pH

5.5 - 5.7

~7.2

Time postmortem

Postmortem metabolism in Brahman

5.3

5.5

5.7

5.9

6.1

6.3

6.5

6.7

0 3 6 9 12 15 18 21 24

pH

Time (h)

Angus

Brahman

#

• More resistant to pH changes• Improved maintenance of energy status (ATP)

Even in death, Brahman are resilient

A role for mitochondria? • ATP production• Calcium sequestration• Mito-mediated cell death Muscle

tone

other

Protein synthesis

Ion gradients Mitochondria

Coupled to ATP

synthesis

Ener

gy fo

r mai

nten

ance

Mitochondria-mediated (programmed) cell death

• Angus, Brangus, Brahman• Caspases?

Caspase content –is lower in Brahman

Little support for a role for caspase postmortem!

Caspase is not cleaved (activated)

Brangus

1 3 6 24h 7 14d

Angus Brahman

1 3 6 24h 7 14d 1 3 6 24h 7 14d

Intact

Calpain gen. Caspase gen.

Mitochondria function postmortem

• At 1h, mitochondria can work and are coupled (produce ATP)• Brahman decrease oxygen consumption at higher temperature

• Does muscle from Angus & Brahman function differently early postmortem?

• Does temperature change functional properties?

Other ways to decrease heat production?Limit mitochondrial leak

Muscle tone

other

Protein synthesis

Ion gradients

MitochondriaCoupled to ATP

synthesis

Ener

gy fo

r mai

nten

ance

Inefficiency(Proton leak)

Brahman vs. AngusMitochondrial function• Longissimus - 1h postmortem

Breed, effect P = 0.02

00.10.20.30.40.50.60.7

breed

Oxy

gen

cons

umpt

ion

(pm

ol/s

/U C

S)

Leak/U CS

Angus Brahman

a

b

Muscle Na/K ATPase and metabolic rate• Increasing fiber size is metabolically advantageous

(Jimenez et al., 2013)• Decreasing surface area:volume reduces metabolic cost of maintaining

membrane potential

SA:V

0

1000

2000

3000

4000

5000

6000

7000

Angus Brahman

area

, um

2

CSA of IIX fibers

Adapted from Wright et al., Meat Sci., 2018

Conclusions• Cellular energy metabolism is an important contributor to heat production

• Several possible adaptations that may help reduce heat production in Brahman

• Muscle function in life may be antagonistic to meat quality parameters. Evaluate and balance consequences for pasture vs. plate.

Thank you!

Funding:Florida Cattle Enhancement BoardNIFA-USDA Product Quality

Heat loss in BrahmanSmooth, slic