Research Results - (PDF, 101 mb) - USAID

years of age resulted in upward trends for milk
and body weight, with the greatest response
observed for culling at eight years. Culling at
five years of age did not increase weight at sale
or milk yield. Instead, production for these ,',o
characters dropped below initial values during
the early stages of selection and returned to
initial values at the end of the simulation.
Average breeding ewe generation number
and average ewe age at the end of each
simulated scenario are reported in table 5. As
selection intensity increased, generation interval
was longer and ewes were, on average, older as
a result of culling intensity. By using rams for
one year, number of generations increased;
therefore, an increase in genetic progress was
simulated. Increasing the rate of genetic change
via the rams did not have an impact on flock
performance. Instead, culling age of ewes
created greater differences between selection
schemes.
These simulations provide insight into
the changes of flock performance as different
selection programs were imposed upon a population
of sheep where there had been no selection
practiced. It was clear that in the harsh
environment simulated, where both meat and
milk offtake are important components of the
sheep enterprise, care must be taken as to the
speed with which programs are implemented.
Using computer simulation provides an additional
tool for animal breeders to use to make a
priorievaluations of selection strategies and
goals and the manner in which these objectives
are obtained.
Resistance to Haemonchus contortus
A. RFLP AnAysis
With the collaboration of the Washington
State University Health project and Dr. R.M.
Waruiru of the Department of Veterinary Pathology
and Microbiology, University of
Nairobi, a total of 95 kids have been artificially
infected with 10,000 H. contortuslarvae to screen
for resistance. These animals are in addition to
those monitored for natural infection. Of these
animals, one doe has shown no detectable level
of infection in fecal egg counts in three separate
artificial infestations. This is an exciting discovery
which may allow a unique opportunity to
map the genes responsible for regulation of
resistance to H. contortus. An embryo transfer
program is planned to create a halfsib family as
large as possible from this doe to augment
existing family data.
In 1987, 134 weaned kids were placed on
a one-year experiment to determine their resistance
to internal parasites. Body weight change,
packed cell volume (PCV), and fecal egg counts
(FEC) were monitored. When PCV and/or FEC
reached critical levels, the kids were drenched
with an anthelmintic. Of the 134 tested individuals,
13 were never treated for parasite load.
Several interesting results emerged from a
summary of the data. Of the 25 sires represented
by their progeny in this test, only six
produced progeny which were resistant or
resilient. The proportion of progeny on test
which were resistant was 3.6% for an EAG buck,
7.4% for two Toggenburg bucks, and 15.4% for a
DPG buck.
Table 5. Effects of culling and ram replacement strategies on
genetic progress, average ewe age, final mature size (WMA) and
potential milk production (GMLKL) after 15 yrs of simulation
Ewe Cull Age (yr)
Ram Replacement (yr)
Generation Number
Average Ewe Age (yr)
WMA (kg)
GMLKL (kg)
Avg Generation /Yr
5 5 6 6 8 8
1 2 1 2 1 2
10.5 5.94 9.62 5.59 8.34 4.93
3.30 3.20 3.80 4.60 4.50 4.80
63.10 50.90 62.20 50.80 59.90 49.70
2.55 2.00 2.51 2.00 2.41 1.95
.70 .40 .64 .37 .56 .33
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