End of Project ReportsReproductive failure in dairy cows results in fewer calves born, lower
milk sales, slower genetic progress and consequently, significant financial
loss to the industry. Dairy cattle breed improvement programmes have,
at least until very recently, focused primarily on increasing the yields of
milk or milk solids. The resulting genetic improvement has led to
significant increases in milk yield per cow but this increase is now
associated with a significant decline in cow reproductive wastage. An
important part of the Teagasc research programme in this area is to
determine the time at which embryo loss occurs and also to determine
whether the extent of the embryo loss is affected by the energy nutrition
of the cow and to devise strategies to reduce its extent. This project has
focused on the relationship between changes in dietary energy intake
near the time of insemination and the extent and pattern of embryo
survival. The main results are summarised in this report and detailed
results of the several experiments involved have been published in the
papers listed at the end of this report.
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4
The objectives of this project were to determine the effect of
changes in energy intake near the time of insemination on
embryo loss rate, on the timing of embryo loss and on the
possible biological mechanisms involved.
Cross bred heifers were provided with either high or low energy
intakes that were based on pasture allowances calculated to
provide either 0.8 or 2.0 times their maintenance requirements.
These energy intakes were allocated for two weeks before and
about five weeks after insemination. The effect of the changes
in energy intake on embryo loss and on the time at which
embryo loss occurred, relative to the time of insemination, was
established. Possible associations between embryo loss and
blood concentrations of progesterone, NEFAs, insulin and
glucose were examined. A sudden reduction from a high to a low energy intake imposed
for two weeks from the day of insemination reduced the
subsequent embryo survival rate by 30 percentage points to a
survival rate of 38%. When energy intake over this same period
was either maintained or increased, embryo survival rate
remained high (overall mean, 69%), within a range of 65-71%.
The time at which embryo loss occurred was established.
Embryo survival or pregnancy rates measured on days 14 and
30 after insemination and at full term were 68%, 76% and
72%, respectively. These results provide new information
indicating that most embryo loss, at least in heifers, had
occurred on or before day 14 after insemination.
There was no evidence of any association between the shortterm
changes in energy intake either before or after AI and
blood progesterone concentration. Neither was there any
evidence that the detrimental effect of the sudden reduction in
energy intake on embryo survival was mediated through
changes in the systemic concentrations of non-esterified fatty
acids (NEFAs) or insulin. There was a suggestion, however, that
the detrimental effect of the reduced energy intake may operate
through a reduction in systemic glucose concentrations.Dairy Levy Farmer Fun
