Endocrine Regulation of Estrus Expression in Dairy Cows

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. Both managerial and biological factors have undoubtedly contributed to the decline in efficiency of estrus detection. The objective of this experiment is 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 will measure concentrations ofLH 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 will also measure daily milk production. Upon completion of this experiment, we may be able to determine I) 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 re]ated to the amount of mi]k being produced. This information will provide the basis for future studies designed to enhance expression of estrus.