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Endocrine Regulation of Estrus Expression in Dairy Cows
W.J. Silvia
Department of Animal and Food Sciences
Project Description
Reproductive efficiency in US dairy herds continues to decline as milk production per cow increases. One factor that contributes to poor fertility is a well documented decrease in the efficiency of estrus detection.
The objective of this experiment was to determine if the occurrence, timing, duration or intensity of estrus is related to the pattern of endogenous estradiol secretion observed during the periovulatory period in 50 lactating cows during the normal breeding period (60-80 days postpartum). We have measured concentrations of LH during this period to determine if the occurrence, timing and magnitude of the LH surge are related to the endogenous pattern of estradiol secretion as well. We have also measured daily milk production. The data collection phase of this experiment has been completed. We are currently analyzing and interpreting the data. Upon completion of this experiment, we may be able to determine 1) if the occurrence and duration of estrus is related to the peak concentration or pattern of endogenous estradiol secretion, 2) if the occurrence and magnitude of the LH surge is related to the peak concentration or pattern of endogenous estradiol secretion, 3) if the relative timing of estrus and the LH surge is related to the peak concentration or pattern of endogenous estradiol secretion, 4) if the peak concentration or pattern of endogenous estradiol is related to the amount of milk being produced. This information will provide the basis for future studies designed to enhance expression of estrus.
Impact
Reproductive performance has become one of the major management problems facing dairy farmers. One of the factors contributing to this decline is a decrease in the efficiency of estrus detection. In 2002, the efficiency of estrus detection from Kentucky DHIA records was just 34%. In 1994, Senger [7] estimated that inefficient and inaccurate detection of estrus cost dairy farmers over $300 million, annually. Previous studies have demonstrated that experimentally induced endocrine deficiencies can result in reduced estrus expression and poor fertility. Results from the ongoing experiment will help to determine if these deficiencies occur naturally and if they contribute to reduced intensity and duration of estrus expression and poor fertility observed in modern dairy cows. Based on the results from this experiment, new management methods will be developed to enhance expression of estrus.