Parturition and periparturient reproductive and metabolic hormone concentrations in prenatally androgenized beef heifers.

Primiparous Angus x Simmental heifers (n = 43) in a single-calf heifer (SCH) system (i.e., heifers are bred, calved, and placed in drylot pens with their calves at side and fed to slaughter weights) were studied to evaluate the effects of prenatal androgenization on parturition and on periparturient reproductive and metabolic hormone concentrations. Seven prenatally androgenized (PA) and seven control (C) heifers were used for blood collection to characterize parturient and lactation endocrine profiles; all heifers were used for blood collection to characterize postpartum ovarian cyclicity. Serum concentrations of progesterone, estradiol, testosterone, 13,14-dihydro-15-keto-PGF2 alpha (PGFM), and prolactin from 10 d before to 3 d after parturition were similar for PA and C heifers. Calf birth weights (34.7 +/- .9 kg) and calving ease scores (1.34 +/- .14) were similar between treatments. Postpartum ovarian cyclicity was similar; only 6 of 22 PA (27.3%) and 3 of 21 C (14.3%) heifers were cyclic by 70 d postpartum, based on weekly serum progesterone concentrations. Serum concentrations of insulin, triiodothyronine (T3), and prolactin at 35, 70, and 105 d of lactation were similar for PA and C heifers; thyroxine (T4) concentrations were similar at 35 and 70 d but greater (P < .01) at 105 d of lactation in PA heifers than in C heifers. Although mean serum concentrations of insulin, T3, and T4 were similar between treatments, prolactin concentrations were greater (P < .05) in C than in PA lactating heifers. We conclude that PA heifers are similar to C heifers with respect to parturition and to periparturient reproductive and metabolic hormone concentrations. Therefore, management requirements of PA primiparous beef heifers seem to be similar to those of C primiparous beef heifers, and PA heifers can be used successfully in a SCH system.