Research Results - (PDF, 101 mb) - USAID

Table 3. Ovulation rate and litter size in pure breeds and
crossbreds
Breed Group N % YMan Ovulation
Rate
Litter Size
S 85 0
DSXS 42 25
F1 57 50
F2 104 50
DX DS 56 75
D 70 100
the underlying genetic basis of reproduction in
these breeds. Table 3 summarizes ovulation rate
and litter size of these two breeds and their
various crosses.
Both the ovulation rate and litter size
increase in proportion to the increase in D'Man
genotype in crosses, which suggests a quantitative
inheritance.
Two papers were accepted, and another
one has recently been submitted, for publication
in the Journal of Animal Science. A total of four
papers were presented at the annual meeting of
the European Association for Animal Production,
and 4th World Congress on Genetics
Applied to Livestock Production (two papers in
each). A paper on repeatability estimates of
litter size is in progress and will be submitted to
Animal Reproduction Science.
Complete citations for these papers are
presented in the "Publications" section of this
report.
U.S.
(Work supported primarily by the California
Agr. Expr. Station but with some SR-CRSP
support, e.g., for computing.)
The transfer of frozen-thawed embryos
was highly successful as shown in table 4.
1.06 1.03
1.41 1.34
1.73 1.49
1.71 1.49
2.31 1.85
2.79 2.00
Table 4. Results of an embryo transfer study
using frozen-thawed embryos
Embryo No. No. %Survival
Classification Transferred Lambs
Good 71 42 59.2
Fair 28 13 46.4
Poor 28 2 7.0
Of embryos classified as fair or good
following thawing, 55% were represented as live
born lambs. However, survival rate of embryos
classified as poor was very low (7%), indicating
that storing embryos of poor quality at collection,
or transferring embryos which are morphologically
abnormal on thawing is not justified.
Most of the poor quality embryos were of
questionable quality when collected; a very high
proportion which were satisfactory at freezing
were also of acceptable quality after thawing,
and the overall results indicate this is a good
method of storing and transforming sheep germ
plasm.
An experiment on the "ram effect" in
inducing out-of-season breeding was completed,
and a paper has been prepared from the resulting
M.S. thesis by W. Cushwa. It was determined
that ewes joined with vasectomized rams
two months prior to the start of the breeding
season showed a higher response rate when
joined with fertile rams. These ewes also
lambed earlier than ewes that were completely
isolated from rams until the regular breeding
season. Data on ovulation rate and embryo
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