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Carry-Over Effects of Periparturient Endocrine Changes on Postpartum Reproductive Function of Holstein Heifers Bred to Genetically Different Service Sires¹

University of Florida, Gainesville 32611

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 µg) and gonadotropin releasing hormone (GnRH; 100 µg). 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>.1). Means and profiles of progesterone concentrations during the first 60 d postpartum did not differ between service-sire-breed groups (P>.1). However, increases in progesterone concentrations following the GnRH-TRH challenge were synchronized more precisely in Angus (P<.02) than in Holstein- and Brahman-service-sire groups. Daily rates of reduction in cervical and uterine horn diameters were higher (P<.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(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 genotype of the conceptus they bore during pregnancy.

¹ Florida Agr. Exp. Sta. Journal Series 6619. This research was supported in part by The Upjohn Co. Kalamazoo, MI.

² Dairy Sci. Dept., Inst. of Food and Agr. Sci.

³ On student leave from Agriculture Canada, Research Station, Lennoxville, Quebec, Canada. Research completed as partial requirements for Ph.D. at the Univ. of Florida.

⁴ Reprint requests: Dairy Sci. Dept., IFAS, Univ. of Florida, Gainesville, FL 32611.

⁵ College of Vet. Med.