Systemic progesterone concentration following human chorionic gonadotropin administration at various times during the estrous cycle in beef heifers.
In Trial 1, 26 heifers were allotted randomly to a control group or one of four groups to receive a single injection of 3,000 IU hCG on d 1, 4, 7 or 10 of an estrous cycle. Heifers next completed a nontreated cycle, and at their third estrus were reallotted to one of the five groups described previously. Estrous cycle length was extended in cycle 1 but was not altered during the nontreated cycle or in cycle 3. Administration of hCG on d 4 or 7 increased (P less than .05) mean serum progesterone (P4) over the first 16 d of the estrous cycle by .9 and .8 ng/ml, respectively. In Trial 2, 23 heifers were allotted randomly to one of two groups to receive a placebo or a single injection of 3,000 IU hCG on d 4 of an estrous cycle. Heifers were inseminated artificially at subsequent estrus. On d 4 postbreeding, treatments were repeated. Administration of hCG on d 4 of the prebreeding estrous cycle increased (P less than .05) mean P4 over the first 16 d by .9 ng/ml, whereas mean P4 over the first 16 d postbreeding was not affected by a second injection of hCG on d 4 postbreeding. Administration of hCG increased (P less than .05) first-service pregnancy rate (92 vs 55%). In conclusion, progesterone concentrations were enhanced by hCG given on d 4 or 7 of the estrous cycle, and pregnancy rate was increased when hCG was administered both on d 4 of the prebreeding cycle and d 4 postmating.
Clemson University, SC 29634-0361.
K F
KF
Breuel
J C
JC
Spitzer
D M
DM
Henricks
D000818:Animals; D001947:Breeding; D002417:Cattle / Q000097:blood*; D006063:Chorionic Gonadotropin / Q000008:administration & dosage / Q000494:pharmacology*; D004971:Estrus; D005260:Female; D011247:Pregnancy; D011374:Progesterone / Q000097:blood*; D011897:Random Allocation; D013997:Time Factors
D006063:Chorionic Gonadotropin; D011374:Progesterone