Dark cutting beefLatest research for pasture-fed cattle
Kate Loudon1
Pete McGilchrist1, David Pethick1, Graham Gardner1, Ian Lean2
1. School of Veterinary and Life Sciences, Murdoch University, Perth, WA, 2. Scibus, Camden, NSW
27 July 2018
Outline
• Dark cutting re-cap
• King Island experiment– Mycotoxins– Minerals
What’s wrong with high pH meat?
Ultimate pH >5.7Meat colour >3
$$$ IMPACT ON INDUSTRYProducer penalty:
avg $0.59/kg HSCW
= $17m per annum
Australian beef industry = $55m per annum
Low muscle glycogen (energy) at slaughter
Time in chiller
pH
5.3ACID
ALKALINE
5.7
7.1
LACTIC ACID
pH6
pH5.5
GlycogenGlycogen
Lactic acid
pH
What dictates muscle glycogen?
Glycogen
Nutrition
Stress Exercise
Predicting muscle glycogen
0.7
0.8
0.9
1
1.1
1.2
1.3
0.25 0.5 0.75 1 1.25 1.5
Need weight gains up hereDanger
zone
Glyc
ogen
(%)
Liveweight gain (kg/day)
Incidence of dark cutting
0
2
4
6
8
10
12
14
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Inci
denc
e of
dar
k cu
ttin
g (%
of l
ots)
SATASVICNational average
Mycotoxins / Minerals ??
Endophytes• Pest resistance• Disease resistance• Drought tolerance
• Can produce mycotoxins –deleterious health effects
• Many classes of mycotoxins:- Lolitrem B- Ergovaline- Ochratoxins- Trichothecenes- Aflatoxins- Fumonsins- Zearaleones- Ergot Alkaloids
Adapted from Biomin effects of Mycotoxins on Ruminants. www.biomin.net
REPRODUCTIVE• ↓ conception rate• Embyronic loss• Abortions• ↓ testicular
development• ↓ sperm production
PERFORMANCE• ↓ feed intake• ↓ feed efficiency• ↓ ADG
GASTROINTESTINAL• Impaired rumen
function• Gastroenteritis• Diarrhoea
DERMAL• Vasoconstriction • Lameness (Laminitis)
NEUROTOXIC• Convulsions
THERMOREGULATION• Heat stress
IMMUNOSUPPRESSIONLIVER DAMAGE
Magnesium – what is it all about?
• Plays a key role in many systems
Magnesium – what is it all about?
Nutrition
Stress Exercise
Glycogen↓ MAGNESIUM(HYPOMAGNESAEMIA)
↑ ADRENALINERELEASE
↑ MUSCLETWITCHING
↓ FEED INTAKE
What causes low magnesium?
↓ MAGNESIUM(HYPOMAGNESAEMIA)
↓ FEED INTAKE
• ↑ K+
• ↓ Ca2+
• ↓ Na+
• ↓ Cl-
‘INDIRECT EFFECTS’IMPAIR Mg2+ ABSORPTION
IN RUMEN
↓ Mg2+ IN PASTURE
• ↑ protein ↓ energy• ↑ moisture diet • ↓ effective fibre• ↑ fertiliser K and N
What causes low magnesium?
↓ MAGNESIUM(HYPOMAGNESAEMIA)
↓ FEED INTAKE
• ↑ K+
• ↓ Ca2+
• ↓ Na+
• ↓ Cl-
‘INDIRECT EFFECTS’IMPAIR Mg2+ ABSORPTION
IN RUMEN
↓ Mg2+ IN PASTURE
• ↑ protein ↓ energy• ↑ moisture diet • ↓ effective fibre• ↑ fertiliser K & N
- Short grass-dominant pasture- Cereal forages- Brassicas
King Island experiment
• 3185 cattle in 66 groups
• Animal / management / environmental factors
Average dark cutting rate
0%
10%
20%
30%
40%
50%
60%16
-Mar
23-M
ar
30-M
ar
6-Ap
r
13-A
pr
20-A
pr
27-A
pr
4-M
ay
11-M
ay
18-M
ay
25-M
ay
1-Ju
n
8-Ju
n
15-Ju
n
22-Ju
n
Dark
cut
ting
(%)
Date (2015)
Ave DFD%Min DFD%Max DFD%
Results #1 Pasture magnesium
0
5
10
15
20
25
30
0.17 0.19 0.21 0.23 0.25 0.27 0.29
Dark
cut
ting
(%)
Pasture magnesium (%)
Results #1: Pasture magnesium
0
5
10
15
20
25
30
0.17 0.19 0.21 0.23 0.25 0.27 0.29
Dark
cut
ting
(%)
Pasture magnesium (%)
PASTURE MG > 0.24%
= 38% DECREASED RISKDARK CUTTING
Results #1: Pasture magnesium
0
5
10
15
20
25
30
0.17 0.19 0.21 0.23 0.25 0.27 0.29
Dark
cut
ting
(%)
Pasture magnesium (%)
PASTURE MG
2015: 73% were below threshold2016: 84%2017: 90%
Pasture calcium0
2040
60Pe
rcen
t
.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5Calcium : Phosphorus Ratio
Bone, muscle function, immunity, energy
**Ca:P ratio CRITICALIdeal 2:1Minimum > 1:1
Calcium deficiency compounded by low magnesium!!
2015: 50% <1:1 (Autumn – Winter)2016 and 2017: 100% < 1:1 (Winter)
What about the other minerals?
• King Island– Copper 10% deficient– Selenium 13% deficient– Zinc 54% deficient
• Copper and zinc: impact on MSA marble score and rib fat depth
• High energy = greater fat deposition
Result #2: Water
• 50% ↑ risk dark cutting in mobs drinking dam water
• ↑ water palatability= ↑ water intake= ↑ feed intake= ↑ glycogen storage
Result #2: Water
• 50% ↑ risk dark cutting in mobs drinking dam water
• Dam pumped straight into trough:– 10-16% ↑ growth rate
• Spring-fed / filtered into trough:– 20% ↑ growth rate
Result #3: Supplementary feed
• 30% ↓ risk dark cutting in mobs fed supplementary feed in the last week before slaughter
• ↑ Metabolisable energy• ↑ Human habituation• ↑ Effective fibre = slower rumen transit rate?• Dilution of mycotoxins?
Result #4: Mycotoxins
• Are out there!– 66 pasture tested
• 100% had >3 major families• 20% had all 6 major families
• My animals don’t have staggers…– 64% Tasmanian beef farmers reported staggers
• SUBCLINICAL EFFECT IS THE GREATEST RISK
Result #4: Mycotoxins
-10000
-5000
0
5000
10000
15000
20000
Ergo
t alk
aloi
ds (p
pb)
Kill date
HIGH dose
What do we do with these results?
1. Magnesium
1. Mycotoxins
• Sheep: Graham Gardner Murdoch University• Short-term supplementation of MgO at 1.0% of the
ration• Exercise trial• Slaughter muscle glycogen measurement
Pre-slaughter magnesium supplementation SHEEP
Pre-slaughter magnesium supplementation SHEEP
Gly
coge
nco
ncen
trat
ion
(g/1
00g)
MgO treatment
0.1.2
.3
.4
.5
.6
.7
.8
.91.0
- +
Pre-slaughter magnesium supplementation CATTLE
• King Island 2016 – 17– GM-free canola meal-based pellet– 46g MgSO4 + 9.5gm MgO / day
…no difference in muscle glycogen
Pre-slaughter magnesium supplementation
MgO
1. glycogen loss associated with stress.
2. rate of glycogen repletion following stress.
Sheep = 1.0% MgO 4days
Cattle…?
Mycotoxins
• Pasture renovation with novel endophyte cultivars
• Mycotoxin binders– Adsorbents bind mycotoxins– Enzyme inactivation and conversion to non-toxic
metabolites
Take home messages
• Pasture magnesium %• Water source• Supplementary feed (seven days before
slaughter)• Mycotoxins
Tools, resources & training
• Pasture mineral testing: $80-100 – Magnesium, calcium, sodium, potassium DM%– Grass tetany index: K / (Mg + Ca) >2.2 = high risk
hypomagnesaemia
• Animal (liver) mineral testing: $15 – $20 / head at slaughter
Kate LoudonMurdoch University
Dark cutting beefLatest research for pasture-fed cattle
27 July 2018
