Abstract
ABSTRACT A study evaluated a 19-h-delayed AI following GnRH administration in a hybrid estrus detection and timed AI protocol. Angus-based, crossbred heifers (n = 453) managed at the Kelly Ranch (Sutherland, NE) or the University of Nebraska West Central Research and Extension Center (North Platte, NE) were synchronized using the melengestrol acetate–PGF2α protocol. Heifers were fed melengestrol acetate for 14 d (d 1 through d 14). Nineteen days later, on d 33, heifers received a PGF2α injection. Heifers (n = 319) expressing estrus were assigned to the first treatment group (EST), were removed from the herd, and received AI 12 h later. Seventy-two hours following the PGF2α injection, heifers not detected in estrus were administered GnRH and randomly assigned to 1 of 2 remaining treatment groups: immediate AI (n = 70, GNRH-I) or AI 19 ± 1 h following GnRH injection (n = 64, GNRH-D). Heifers artificially inseminated that had exhibited estrus had greater (P
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