Periparturient endocrine changes of conceptus and maternal units in Holstein heifers bearing genetically different conceptuses.

Holstein heifers (n = 21) were balanced across sires and assigned to three service-sire-breed groups in which heifers were inseminated artificially to either purebred Angus (n = 7), Holstein (n = 7) or Brahman (n = 7) bulls. Semen from four bulls was used for each service sire-breed group. Blood samples were collected from a jugular vein thrice weekly from d 160 to 265 of pregnancy, daily thereafter until 15 d postpartum, and then thrice weekly until d 60 postpartum. Concentrations of progesterone, estrone, estradiol, and estrone sulfate from 23 d prepartum to parturition, and of 15-keto-13,14-dihydro-prostaglandin F2 alpha (PGFM) from 2 d prepartum to d 15 postpartum were measured by radioimmunoassay. Heifers within the Brahman-service-sire group had longer gestations (P less than .05) than those of Holstein- or Angus-service-sire groups (285.0 vs 278.7), 279.0 d). Calf birth weight was lower (P less than .05) in Angus- than Holstein- and Brahman-service-sire groups (30.6 vs 36.1, 43.4 kg). Daily trends of prepartum maternal progesterone concentrations were approximately 1 ng/ml lower (P less than .01) in Angus- than Holstein- or Brahman-service-sire groups until luteolysis occurred. Heifers bearing crossbred Angus conceptuses had lower daily trends of prepartum estrogens concentrations (P less than .01), whereas heifers of the Holstein- and, even more dramatically, of the Brahman-service-sire groups had a higher magnitude and greater rise of plasma estrogens concentrations between d -10 and -1 prepartum (less than .01). Postpartum mean concentrations (P less than .05) and response curves of PGFM were lower (P less than .01) in the Angus- than in the Holstein- or Brahman-service-sire groups. Calf birth weights were correlated with least-squares means for maternal concentrations of prepartum estrone (r = .57), estradiol (r = .59) and estrone sulfate (r = .64) and postpartum maternal concentrations of PGFM (r = .56). Functional responses of the conceptus (e.g., estrogens) and maternal units (e.g., progesterone and PGFM) were influenced by conceptus genotype during the periparturient period.