management to improve lamb survival
TRANSCRIPT
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Management to improve lamb survival
Susan Robertson
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What is normal?
•20% of lambs die (10% of singles, 30% of twins)
•90% of lamb deaths within 7 days of birth
•On-farm range in mortality: 4 to 50% of singles 15 to 85% of twins
Most at risk: Merino, multiple births, from maidens
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Why do lambs die?
Cause of death % of all deaths
Starvation/exposure/mismothering/
} 80lambing difficulty
Primary predation
} 20Infection
Deformities
Other
Target the major causes to improve survival
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Adequate nutrition is critical
•Condition score 3.0
•1200 kg DM/ha + (green)
to 1800 kg DM/ha
Source: King et al (1990) ASAP 18, 272
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Short-term feeding to increase colostrum
•0.5 kg/ewe/day (lupins, maize, barley) for 7 days before
lambing ↑ colostrum
•7 days before + first 7 days of peak lambing ↑ survival by
7%+
•Ineffective where ample green pasture
•Response is variable - Calculate cost vs extra lamb value
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Is exposure to weather a risk?
•Exposure contributes to 60% of lamb deaths (SME)
•Hot weather? Provide shade, minimise distance to
feed/water
•Cold, wet, windy weather:
critical level: chill index > 1000 kJ/m2.hour
Proportion of lambs dying due to chill at different lambing dates at Ginninderra
Twins---SinglesSource: Donnelly et al (1984) AJAR
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Likelihood of median daily chill index exceeding 1000 kJ/m2.hr for 24 weekly
periods from May to October with 0 (- ● -), 25 ( ּ ּ ○ ּ ּ ), 50 (--▼--), 75 (··-∆-··) and
100 (–■–) % wind speed reduction at different locations
0% wind reduction
100% wind reduction
Median value for each week means 4 out of 7 days exceeds 1000 kJ/m2.hrThe potential for
shelter to reduce chill index differs with location and month
Reducing wind speed has a much larger effect on the incidence of high chill days at windy locations
Source: Broster et al (2012) Animal Production Science 52, 921-928.
Hamilton
Temora
Tarcutta
Orange
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Can shelter from wind improve survival?
•Paddock shelter alters wind speed, not rain or temperature
•Lambing in cold, windy weather
•Benefits more likely in twins, Merino
•At Tarcutta (Jul/Aug):
Shrub shelter 77% survival of twins, hessian 70%
No increase in single lambs
•At Hamilton: 50% increase in survival with tall grass rows
singles and twins
•Shearing pre-lambing?
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Economics of shelter
• The profitability of shelter depends on the cost of shelter,
the twinning rate, and how much survival is increased
Percentage increase in lamb survival required to obtain a positive NPV from shelter
Base survival 60%
(Source: Broster 2014)
Shrubs$3500/ha
25 yr tree life
6
8
10
12
14
16
1500 1750 2000 2250 2500 2750 3000 3250 3500 3750
Incr
eas
e in
lam
b s
urv
ival
(%
)
Cost of shelter ($/ha)
20% twins
Shrubs$3500/ha
25 yr tree life
6
8
10
12
14
16
1500 1750 2000 2250 2500 2750 3000 3250 3500 3750
Incr
eas
e in
lam
b s
urv
ival
(%
)
Cost of shelter ($/ha)
20% twins 40% twins
Shrubs$3500/ha
25 yr tree life
6
8
10
12
14
16
1500 1750 2000 2250 2500 2750 3000 3250 3500 3750
Incr
eas
e in
lam
b s
urv
ival
(%
)
Cost of shelter ($/ha)
20% twins 40% twins 60% twins
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Natural shelter can be cheap
Consider opportunity costs of lost grazing
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Does high stocking density reduce lamb survival?
• 14.3 ewes/ha or 143 ewes/ha - same lamb survival
(Winfield 1970)
•2.9 ewes/ha to 23.9 ewes/ha – same lamb survival but
optimum flock size 400 ewes (Kleemann et al 2006)
But…
•AWI currently funding mob size research
8 or 15 twin-bearing ewes in 0.5ha = 16 ewes/ha 30 ewes/ha
Proportion lamb survival of live births 0.83 a 0.63 b
Source: Robertson et al (2012)
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Maternal experience: maidens 10% lower survival
Can lamb survival from maiden ewes be increased through pre-lambing exposure to adult lambing ewes?
Exposed Not exposed
Proportion lamb survival 0.53 0.61
Lambs marked/ewe 0.71 0.78
Source: Robertson et al. in press
Lamb maidens in separate paddocks from mature ewes.
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Conclusions
•Relatively simple management changes can improve lamb survival
•Target management for specific conditions
•Consider the cost: benefit of strategies, and opportunity costs
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