SELECTION OF GENETICALY RESISTANT SHEEP AGAINST GASTROINTESTINAL NEMATODES. A CASE STUDY Armando Nari FAO. Italy

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SELECTION OF GENETICALY RESISTANT SHEEP AGAINST
GASTROINTESTINAL NEMATODES. A CASE STUDY
Armando Nari FAO. Italy
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SHEEP RESISTANCE/RESILIENCE THE ICEBERG CONCEPT
POTENTIAL SELECTION FOR RESISTANCE/ RESILIENCE
CONVENTIONAL APPROACH BY FARMER
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THE GENETIC RESISTANCE APPROACH TO MANAGING
PARASITES REQUIRES SIGNIFICANT COMMINTMENT

• ... IT WOULD TAKE PRODUCERS 10-15 YEARS TO
  BUILD UP SIGNIFICANT PARASITE RESISTANCE WITHIN
  FLOCKS
• R. Woolaston, 1997

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e.p.g
Decreased resistance
Control
years
Increased resistance
Resistance to worms can increase
significantly after 8-10 years
CSIRO, Armidale, Australia
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COUNTRIES WITH ANTHELMINTIC RESISTANCE IN THE
AMERICAS FAO- OIE SURVEY
2004 Nicaragua
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HOST RESISTANCE AND RESILIENCE
RESISTANCE The hosts ability to limit the
establishment growth rate, fecundity and/or
persistence of a parasite population.
RESILIENCE The ability of the animal to grow
and produce in spite of the presence of a
normal worm burden
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GENETIC RESISTANCE OF SHEEP

• BETWEEN BREEDS. Some breeds have naturally
  higher
• genetic resistance. These breeds have evolved
  different
• mechanisms of resistance. By crossing resistant
  breeds a
• synthetic population of highly resistant sheep
  can be
• obtained (ILRI, IAEA)

• BETWEEN INDIVIDUALS. There is a widely genetic
  
• variability within flocks which allows
  selection for
• resistance to gastrointestinal nematodes
  (CSIRO,
• FAO/URU)

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RED MAASAI SHEEP
Leyden Baker Alan Carles, 2001
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HOST RESISTANCE AND BREEDS
BREED
N
Peak FEC
Deaths
Hampshire
10
20,000
10
Corriedale
10
10,000
6
Dorper
10
8,000
3
Merino
10
4,000
4
Black Head Persian
10
3,000
3
Red Maasai
10
300
0
Natural pasture challenge over 2 years.

Preston and Allonby (1979)
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GENETIC ANIMAL RESISTANCE
COUNTRY
RESISTANT SHEEP BREEDS
Kenya
Red Masaai
USA
Florida Native
Lousiana Native
Navajo
St. Croix
Barbados Blackbelly
France
Lacaune
Britain
Scottish Blackface
Australia
Merino (selected lineage)
New Zealand
Romney
Perendale (Cheviot x Romney)
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MORTALITY
SEMI-ARID
HUMID
27
Mortality ()
EWES
22
17
Less mortality
12
Less mortality!
7
2
62
52
LAMBS (Birth 12 months)
42
Mortality ()
32
22
Less mortality
Less mortality!
12
2
D
D
RM
RM
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RESISTANCE-6 MONTH LAMBS
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SEMI-ARID
HUMID
27
26
25
Higher PCV
PCV ()
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Higher PCV
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22
21
20
13500
11500
9500
GFEC (epg)
7500
Smaller GI burden
5500
Smaller GI burden
3500
1500
D
D
RM
RM
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BACKGROUND
Haemonchus contortus (43 ) Trychostrongilus
colubriformis (26 )T.axei (12) Nematodirus
spp. Nari et al (1977)
Survey at national level 92.5 farms/flocks
affected (BZ 86, IMZ 71, ML 1.2 ). Nari et
al.(1994) V
Yearling lambs (without treatment/efficacy)
Mortality 50, Live weight 23 wool production
29 . Castell et al (1995)
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- Uruguayan Wool Secretariat - DILAVE Miguel C
Rubino
- DNA PCR gene characterization
(Lessa et al, 2002) - Faecal Egg Count (FEC)
Heredability 0.2-0.3, with neutral or
slightly negative correlation with weight
and wool traits
- Previous work. Castell Cardellino (1994) -
TCP/URU/8921 (A). Genetic resistance in sheep
to gastrointestinal nematodes in Uruguay (1998)
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DISTRIBUTION OF CORRIEDALE LAMBS IN ACCORDANCE
WITH FECAL EGG COUNTS (FEC)
SHEEP N
Arithmetic mean 1737 (e.p.g) n lambs 310
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Management requirements for measuring RESISTANCE

• Ewes and lambs always graze together
• All ewes and lambs get the same feed (forage and
  supplements)
• All ewes and lambs receive the same health
  treatments (drugs, vaccines, dewormers).

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Measurement of resistance in Sheep Breeds
Lambing
Months
Monitorig small number of samples at two week
intervals
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Corriedale genetic lines and TCP/URU/8921
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RESISTANT VERSUS SUSCEPTIBLE LAMBS (2003
PROGENY)
FEC
5.5 8 11 months
Haem. 93 Trich. 89 Haem. 54/Trich 42
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ESTIMATED PROGENY DIFFERENCE (EPD) VALUES FOR
FAECAL EGG COUNTS
0.49
E P D
-0.39
H2 0.18 /- 0.03 Best Linear Unbiased Prediction
(BLUP)
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CORRIEDALE RESISTANT NUCLEUS IN URUGUAY
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PROSPECTS FOR A BREEDING PROGRAMME OF RESISTANT
SHEEP IN URUGUAY

• Culling of more susceptible
• animals (FEC)

• Test of rams at the Progeny
• Central Testing farms

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CONCLUSIONS

• Until novel and more practical methods for
  genetic
• selection are developed it is possible to use
  FEC for
• the detection of resistance to
  gastrointestinal
• nematodes in sheep

• Breeding programmes for nematode resistance
• are compatible with most IPM strategies
  whenever
• there is adequate planning and follow up

• Countries and farmer associations should support
  
• breeding strategies as a sustainable
  alternative to
• minimize the productive impact of
  gastrointestinal
• nematodes in sheep

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