heat tolerance and tenderness - uf/ifas
Post on 31-Jan-2022
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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.
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