Norgestomet implants maintain pregnancy in ovariectomized heifers

Fifty-five heifers were synchronized with norgestomet and estradiol valerate and artificially inseminated approximately 48 h after the removal of norgestomet implants. Ten days after AI, 15 of the heifers were ovariectomized and then two 15 mg norgestomet/silicone implants were implanted subcutaneously on the convex surface of the ear. The norgestomet/silicone implants were changed every 55 +/- 4 d (mean +/- range) thereafter, and the last set of implants was removed 273 d after AI. At 44 d after AI, 65% (26/40) of the control heifers and 53% (8/1 5) of the ovariectomized heifers with norgestomet implants were pregnant (P > 0.10). Two pregnancies were lost in ovariectomized heifers treated with norgestomet (44 to 96 d after AI) and a third pregnancy failed in a heifer that lost 1 of 2 implants 65 to 96 d after AI. Ninety-six days after AI implants were removed from 2 pregnant ovariectomized heifers with norgestomet implants. These 2 heifers were open at 116 d after AI. All 3 ovariectomized heifers with norgestomet implants pregnant at 273 d after AI calved an average of 41 h after the removal of the last set of norgestomet/silicone implants. Dystocia (P < 0.05), retention of fetal membranes (P < 0.01), and calf mortality (P < 0.01) were higher for the ovariectomized heifers with norgestomet implants than for the control heifers. (C) 1997 by Elsevier Science Inc.