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 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.