Download Research Update from the US Meat Animal

Research Update from the U.S.
Meat Animal Research Center
Kreg Leymaster
USDA, Agricultural Research Service,
U.S. Meat Animal Research Center,
Clay Center, NE
USDA is an equal opportunity provider and employer.
Number of ewes exposed in 2014.
Breed/Project
2014
Dorset
141
Romanov
154
Production System project
1,806
Katahdin
(434)
Polypay
(491)
Easycare
(881)
OPP project
Total
480
2,581
Background for production system project
Reducing labor per ewe is one of the best opportunities to
increase profitability and attract new investments to the industry.
One approach is to use “easy care” genetics
in a low-input, pasture-lambing production system.
Romanov provided the genetic foundation for ewes.
Identified breeds that complement Romanov germplasm.
The strategy was to create well-balanced levels
of prolificacy and maternal ability in Romanov
crossbred ewes to realize acceptable lamb survival.
Dorset
Rambouillet
White Dorper
Dorper
Katahdin
Characteristics of production systems
High-input system
Lamb in a barn in March
Provide harvested feed (silage) to ewes
Assist births
Dip navels in iodine
Pen ewe and newborn lambs
Limit ewes to rearing 2 lambs
Rear extra lambs in nursery
Provide creep feed
Weigh at 0, 8 (weaning), 12, and 24 weeks of age
Low-input system
Lamb on pasture in May
Only tag lambs at birth
Weigh at 8, 12 (weaning) and 24 weeks of age
Move lambs to feedlot after weaning
Scope of the experiment
Prod
system
Sires of
ewes
Number
of ewes
Matings
Litters
Lambs
High
72
391
1,044
902
1,985
Low
72
439
1,185
1,060
2,186
Total
72
830
2,229
1,962
4,171
Survival rate to 8 weeks of age for lambs born as
singles or twins to 1-, 2- and 3-year-old Romanov
crossbred ewes in the low-input production system
Age of ewe
Singles
Twins
1-year-old
83.0
72.0
2-year-old
87.0
90.5
3-year-old
85.0
89.5
Relative to singles, it is not a challenge for 2- and 3-year-old
Romanov crossbred ewes to raise terminally-sired twins.
211 sets of triplets were born to 2- and
3-year-old Romanov crossbred ewes.
3% of ewes raised 0 lambs.
10% of ewes raised 1 lamb.
40% of ewes raised 2 lambs.
47% of ewes raised 3 lambs.
Means of Romanov crossbred ewes for
fertility rate during May breeding (phase 2)
Fertility Rate, %
95
90
85
80
75
RB
DS
DP
WD
KT
Develop an easy-care maternal line of prolific hair sheep that can
raise triplets on pasture without labor or supplemental feed.
1/2 Romanov
1/4 Katahdin
1/4 White Dorper
Selection goals for easy-care rams
Manage genetic diversity
Structurally sound
Healthy
White
Polled
Shed hair/wool
Reared as triplets
Genetically resistant to scrapie
Genetically less susceptible to OPP virus
Genetic controls for evaluation of
the easy-care maternal line
Polypay
Katahdin
Prominent maternal breeds of prolific wool and hair sheep.
Evaluation of maternal breeds and mating systems in a
low-input, pasture-lambing production system
Katahdin and Polypay used as standards for hair and wool breeds.
Produce purebred ewes in 2013, 2014 and 2015 for evaluation.
Ewes mated to produce purebred and terminally-sired lambs.
Use multiple-sire breeding in both mating systems.
Use parentage testing to determine sires and dams.
Evaluate productivity through four parities.
Number of ewes per breed and mating system
for lambing in 2014.
Mating system
Breed of ewe
Purebred
Terminal
Katahdin
65
65
Polypay
72
70
Easycare
70
71
Productivity of Katahdin, Polypay, and Easycare ewe
lambs in the production system experiment in 2014
Maternal
line
Ewes
exposed
Ewes
lambed,
percent
Lambs
born
Lambs
weaned,
percent
Lambs
weaned per
ewe exposed
Katahdin
130
83.1
1.26
80.1
0.84
Polypay
142
76.1
1.29
70.5
0.69
Easycare
141
92.2
1.68
83.5
1.29
These are preliminary results!
Evaluation of ewe productivity through 4 parities
Year of evaluation
Birth year
of ewe
2014
2015
2016
2017
2013 (400)
x
x
x
x
x
x
x
x
x
x
x
2014 (400)
2015 (400)
2018
2019
x
Path to discovery of a gene affecting susceptibility
to OPPV infection.
Sheep Resources
69 matched pairs of
infected and uninfected
5- to 9-year-old ewes.
Provide DNA and infection
status.
Genomic Tools
TMEM154
The TMEM154 gene is predicted to encode
a membrane protein
OPPV
Different versions of
TMEM154 are encoded in
sheep and some versions
are associated with
greater susceptibility to
infection.
Viruses bind to the “outside” part of membrane proteins.
Experimental procedures
20 sentinel lambs were naturally reared by uninfected dams.
187 trial lambs were naturally reared by infected dams.
Dams were the same crossbred type and 5 and 6 years of age.
All dams and lambs were comingled.
All lambs (ewes, wethers) were bled 1 week after weaning
and every 5 weeks thereafter until about 9 months of age.
The diplotypes of lambs were determined and concentrations
of anti-OPPV antibody at each sample date were measured.
Probability of infection at 9 months of age
by TMEM154 diplotype of lamb
TMEM154 diplotype
Probability of infection
“1 1”
0.094
“1 3”
0.323
“3 3”
0.346
The probability of infection at 9 months of age for lambs
with either diplotype “1 3” or “3 3” averaged 3.56 times
that of lambs with diplotype “1 1”.
Effects of TMEM154 diplotypes on susceptibility to OPP virus infection
100
"3 3"
"1 3"
"1 1"
90
Percentage infected
80
70
60
50
40
30
20
10
0
8
12
16
20
24
28
32
Age at testing, mo
36
40
44
Genetic variations in TMEM154 and the OPP virus
interact to affect susceptibility to infection.
OPP viruses can evolve rapidly due to high mutation rates.
There are two genetic subgroups of OPP virus in the US.
Both subgroups can infect sheep with haplotypes 1, 2 or 3.
Association of OPP virus subgroups with
TMEM154 diplotypes of infected sheep.
OPP virus subgroup
TMEM154
1
2
“1 1”
More likely
Less likely
“2 2”, “2 3” and “3 3”
Less likely
More likely
Important results from this experiment.
Proved that TMEM154 affects susceptibility to OPPV infection.
Established that haplotype 1 is recessive to haplotype 3.
Documented that 67% of the genetically most-susceptible lambs,
raised by infected old ewes, were not infected by 9 months of age.
“1 3” and “3 3” ewes were 90% infected by 43 months of age,
in stark contrast to “1 1” ewes.
Therefore, the primary cause of lifetime infection is likely due
to non-maternal exposure that occurs after naïve ewes join a flock
of infected breeding ewes.
The key management strategy is isolation of young ewes to
to prevent subsequent non-maternal exposure.
Two additional ongoing experiments
•
Evaluate effects of haplotypes 2 and 3 on lifetime infection.
•
Evaluate effects of haplotypes 1 and 4 on lifetime infection.
Search for additional genes affecting susceptibility
Sheep Resources
69 matched pairs of
infected and uninfected
5- to 9-year-old ewes.
Provide DNA and infection
status.
Genomic Tools
Original chip only had 50,000 markers.
Now sequencing entire genome to give
about 3 billion genotypes per sheep
(77 of 138 sheep completed).
Collect about 500 billion genotypes each
week.