Fertility in estrus-cycling and noncycling virgin heifers and suckled beef cows after induced ovulation.

A procedure was developed to either induce or synchronize ovulation in heifers and suckled cows. Beef females were assigned to two breeding programs: 1) two injections of prostaglandin F2alpha (PGF2alpha) given 14 d apart to synchronize estrus (PGF2alpha control; n = 179), with inseminations 12 to 16 h after detected estrus or at 80 h in the absence of estrus, or 2) two injections of PGF2alpha (d -14 and 0) plus 100 microg of GnRH on d -7 when 6 mg of norgestomet was implanted (PGF2alpha/NORG/GnRH treatment; n = 173). Implants were removed 24 h after the second PGF2alpha injection (d +1) and females were inseminated 12 to 16 h after detected estrus until 54 h after PGF2alpha. The remaining cattle were given a second 100-microg GnRH injection 54 h after PGF2alpha and inseminated 18 to 20 h later. Percentages of noncycling females with subsequently elevated progesterone (P4) on d 0 or +1 were not different between treatment groups (20.4 vs 25%), but conception rate was greater (P < .05) in noncycling treated females than in noncycling controls (55 vs 12.8%). Conception rates in cycling (59.2%) and noncycling (62.2%) treated females were similar to those in cycling controls (56.2%) but greater (P = .06) than those in noncycling controls (26.5%). Conception rates in treated females inseminated 12 to 16 h after detected estrus (63.1%) or at one fixed time (58.3%) were similar to those in controls inseminated 12 to 16 h after detected estrus (68.7%). This treatment procedure produced fertility after one timed insemination that was equal to controls inseminated after detected estrus and induced equally fertile ovulations in noncycling heifers and cows.