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Carry-over effects of periparturient endocrine changes on postpartum reproductive function of Holstein heifers bred
Abstract:
Effects of fetal sire on postpartum reproductive changes of the dam were studied in 21 Holstein heifers whose pregnancy had been initiated by either Angus (n = 7), Holstein (n = 7) or Brahman (n = 7) bulls. After parturition, all heifers were managed uniformly. Heifers in each service-sire-breed group were bled via jugular venipuncture thrice weekly from d 160 to 265 of pregnancy, daily thereafter until 15 d postpartum, and three times per week until d 60 postpartum. Ability of heifers to release prolactin (PRL) and luteinizing hormone (LH) was evaluated on d 10 postpartum after a simultaneous injection of thyrotropin releasing hormone (TRH; 100 micrograms) and gonadotropin releasing hormone (GnRH; 100 micrograms). Between d 5 and 60 postpartum, the reproductive tract of each heifer was examined rectally thrice weekly after collection of blood samples. Basal concentrations of LH from d 1 to 10 postpartum, as well as ability of the pituitary gland to release LH and PRL after the GnRH-TRH challenge, did not differ between service-sire-breed groups (P greater than .1). Means and profiles of progesterone concentrations during the first 60 d postpartum did not differ between service-sire-breed groups (P greater than .1). However, increases in progesterone concentrations following the GnRH-TRH challenge were synchronized more precisely in Angus (P less than .02) than in Holstein- and Brahman-service-sire groups. Daily rates of reduction in cervical and uterine horn diameters were higher (P less than .01) in Holstein- and Brahman- than in Angus-service-sire groups and were associated with higher profiles of postpartum 15-keto-13,14-dihydro-prostaglandin F2 alpha (PGFM) concentrations. Within-cow PGFM concentrations were correlated positively with cervical (r = .36) and uterine horn (r = .32) diameters. Postpartum ovarian responsiveness and uterine involution in Holstein heifers may be affected by genotypes of the conceptus they bore during pregnancy.