Fluctuations in Energy Intake and Fertility in Cattle.

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. • • 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