AuthorYoung, William McFerrin
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThe object of this investigation was to measure the changes in plasma corticoids and progesterone, at two different levels of energy intake during the postpartum period in beef heifers and to assess their relationship to breeding efficiency. Blood samples were taken using a tail bleeding method from 26 first calf crossbred heifers within 24 hours postpartum. Sampling was continued twice weekly until each animal was diagnosed pregnant. Plasma samples were analyzed for progesterone and corticoids using competitive binding techniques. Progesterone levels increased from .5 ng/ml postpartum to 3.7 ng/ml following first ovulation. These levels remained high if conception occurred (5.0 + ng/ml) or returned to minimum levels for repeat estrous cycle. Due to the necessary manipulation of the animals, postpartum plasma levels of corticoids fluctuated widely (10 ng/ml to 70 ng/ml) for each animal. Corticoids means were lower during the postpartum anestrum than during subsequent estrous cycles. No significant correlations were found between plasma corticoids and progesterone concentrations. Providing more than NRC recommended energy intake had no influence on breeding efficiency.
Degree ProgramAnimal Science